Tony - What happens, with regards to diffraction, when I put a 2x extender on my 300mm f2.8 lens? I realize that I'm shooting at F5.6, losing 2 stops, but does diffraction come into affect quicker, or differently, because of the 2-stop loss?
@@sfink16 I take it the 300/2.8 is a prime of some sort. At 5.6 the diffraction should still be ok. Most of the time it becomes noticeable after F11 and up.
Tony - diffraction occurs for any wave that travels through a slit no matter the size, given by a specific math formula. For a circular (or close to it in terms of relative differences) aperture this creates a diffraction pattern known as an Airy disc and described by the approximate formula sin(x) = 1.22*(wavelength/diameter) where x is the angle of first minimum, and is often used as the size of the disc (in reality a bit more complicated). The reason softness occurs due to diffraction is if the Airy disc is larger than the pixels receiving the information, because it can no longer distinguish two point sources cleanly. The aperture at which this occurs is known as the diffraction limited aperture, which is the largest aperture at which the Airy disc is so much bigger than the pixels size of the sensor that two point sources start overlapping the pixels that record them. Usually we use 2-3 (the popular online calculator uses 2.5) pixel sizes for which there will be softening. In the camera world the previous formula can be further approximated by x = 2 * 1.22 * wavelength * Fnumber. Using 525nm (green, assuming everything is corrected to this wavelength as a simplication) and f16 you get 20 microns. A 5d4 has a pixel size of 5.36 microns and a 7d2 has a pixel size of 4.1 microns so both would see the soften effects of diffraction. In reality with Bayer sensors you have more green pixels so they would technically hit DLA sooner. Note this formula assumes 100% pixel peeing at typical computer distances. As that is relaxed the DLA increases.
Thanks for a clearly expressed method to calculate diffraction... more useful to photographers than the underlying theory - which at some level always becomes "because it does" to anyone.
I AM a physicist. And the explanations below about Airy circles are correct. The f/stop diffraction has nothing to do with sides of aperture. The best way i can explain it to the photographers is that passing light through an aperture turns that light from hard to soft. The effect is allot more pronounced when size of aperture is close to wavelength of light; but the effect is there for all apertures and all wavelengths. Explanation by Antonio Sanchez in the comments is correct. Also, making smaller pixels does not make diffraction worse; it enables you to see blur from diffraction better.
A physicist huh? We are all super impressed. You should use that big ole brain that perfectly understands diffraction to figure out the difference between a lot and allot.
While the practical meaning of your video is right, the science or your guesses are quite off. Diffraction has long been understood, it is just damn complex math if you want all to be right, similar to semiconductor theory, a mess if you want to calculate stuff. Some other commenters already pointed out useful resources for the correct info. Love the community!
Physicist here: Single slits also produce diffraction, of the same kind as the double slit experiment. It will produce two things, first of all an interference pattern, where you see concentric circles, dark and light. Second, the light will be diffused from the straight path and will travel in all directions, although most of it will be concentrated along the original path. There is a characteristic angle that measures the size of these effects, and it is given by the wavelength of the light (around 500 nm) divided by the size of the slit (around 2mm), so about 0.00025 radians. This is a very small angle, but it is about angular size of the pixels of your camera as seen from the diafragm of your lens. So you will see these effects on your camera. I dont do optics, but it should possible to put concrete numbers on these effects (e.g. the angle to the first destructive interference, or the angle that contains 90% of the energy)
It seems like if you're willing to make the sensor larger, you could keep your apertures larger, and it would improve the *angular* effect. Is the slit creating a bandlimited impulse or somesuch like you'd see in a 1d bandlimited signal? Would a (spatial) low pass filter prevent some of the interference (just as a low pass filter prevents aliasing in a bandlimited signal)?
@@microcolonel But then you would decrease your DOF, I am not sure if there is some optical trick to overcome diffraction and obtain a photo with the same DOF. Maybe it is possible to remove most of it computationally. In any case, the advantages of having most of your subject in focus for macro photography outweighs the resolution loss due to diffraction.
I am a Physics student at Purdue University (not a grad student or a professor, but I am graduating soon). Stopping down the lens still uses all the lens. The difference is that light coming in at more extreme angles (through the edges of the lens) are removed by the aperture. That removal of high incident angle light makes the focus point sharper because the centers of lenses are generally free of aberrations (the edges are much harder to get perfect). In laser laboratories, it is not uncommon to shoot the laser through the center of a large and cheap lens rather than through a small and expensive achromatic lens (the centers of lenses generally don't produce the same amount of chromatic aberrations). The reason that I say that the whole lens is still used is because the whole scene is still visible. Using less of the overall glass would be the same as masking (note that mirror lenses behave differently to masking, there it is more like an aperture (personal experience)). The blur from high f-numbers is most similar to the "knife edge diffraction." The light does interact with itself and the pattern can be seen in water (Huygens's principle).
So, no matter what my camera or lens is, the first thing to do as a landscape shooter is to stack in a steady environment could be inside or out outside and take a series of photos to each F/STOP and check where the lens sweet sharp F/STOP is and I will do this on infinity focus because that's what I do most of the time.
Rule of thumb - if your lens goes to F22 dont go over (halfway) F11 or if lens maximum is F16 dont go over F8. It would be a good test whether ND filter is worse image quality than lens diffraction for long exposures
Great topic. I’m an electrical engineer and astrophotographer (with telescopes), not an optical physicist. But the math for diffraction is pretty darn simple on a basic level. Instead of talking about aperture as a focal ratio, it is simpler to talk about it as a diameter or radius, r, of the physical aperture. Light near the edge of the aperture is bent. Light away from the edges in not. So just look at the ratio of the aperture edge (bent light) to aperture area (unbent light). Edge = Circumference is C=2*pi*r. Area is A=pi*r^2. C/A = (2*pi*r)/(pi*r*r) = 2/r. So diffraction is inversely proportional to aperture radius. Also, not sure about those waves - maybe a secondary effect? But as a first effect, some photons are nearer to edge than others, so they get bent more. Some are in middle of aperture and don’t get bent. Others are at the opposite edge of aperture, and get bent the opposite way. That is why the light scatters and an image point becomes distributed (i.e. blurry). We can call this the airy disk. This is essentially the single-slit experiment. If the single slit (aperture) becomes small enough to approach the wavelength of light, the diffraction rings show more strongly. If we have a longer focal length, then we magnify it more and it is easier to see (or it spans more pixels so the sensor can resolve it). Another point on shooting through glass (especially thick aquarium glass): a big aperture collect light that passes through a bigger area of the glass, so you see the variation across the glass. Telescopes through windows are very bad. My Fuji APS with 56mm f/1.2 is very bad at the aquarium. My iPhone with tiny sensor and tiny aperture radius is very good through the aquarium glass because the thick glass doesn’t vary much across the tiny couple of millimeters of aperture. Essentially, cheap glass is the same issue as lens aberration, only worse.
Toby Bass Videos about quantum physics are helpful too. It sounds really unintuitive that the photons “know” the gap is small and have to have a less precise position, but that’s just how it works at that scale.
@@Ty4ons You don't really need QM for this. The math was done in the mid to late 1600s. The only tricky part is understanding the limits for diffraction to occur. He seems to think that light is a particle in his explanation (he acknowledged the wave nature but doesn't quite internalize it). The best explanation is the diffraction caused by a razor blade.
@@tobylukebass6234 it is not about 'belief' it is about the physics and understanding a very simple point, no one actually understands why diffraction happens. Lookup the double split experiment , plenty of UA-cam other material. Huygens is just away of thinking about it not actually what happens. Or read QED by Richard Feynman then say you understand the subject.
I'm not a physicist myself, but I think this is all well-understood. And it is not to do with electrons in the iris attracting photons. It is just a result of the wave nature of light. You can see the same effect on waves on the surface of water, for example. The light bends around apertures as would any wave. Light at the aperture acts as a wave front, resulting in the light spreading out.
Technically, diffraction happens at all scales with all waves, and it's just that the significance it has is smaller as the size of the aperture gets larger relative to the wavelength. The thing about photons traveling as waves is a bit off, though you mention phase differences, there are also wavelength differences. Even so, diffraction still happens with coherent monochromatic light -- you can diffract research-grade lasers, for instance. The behavior at the photon level is largely statistical, and the wave behavior is the statistical distribution that follows the pattern of that wavefront. The general fit for the behavior at the aggregate scale is basically a Fourier Transform of the aperture shape. This is the model we also use to simulate not just lens aperture bokeh, but even things like glare as perceived through one's own eye. Of course, in practice, this is compounded by the fact that you anyway have some variance caused by passing through glass on the way to the aperture, and then more again after. To be exact, the Fourier Transform is basically equivalent to Fraunhofer diffraction, and technically Fresnel diffraction is more correct (and appropriate for things like glare through the eye), but the significance of the Fresnel component at far field distances -- and the distance between a lens aperture and the camera sensor would qualify as "far" in this scope -- is basically zero, so it just reduces to Fraunhofer diffraction.
Diffraction is actually a fairly fundamental phenomena shown by light and can easily be understood using the wave theory of light. Basically in order to understand it, think of light as a wave. Imagine a wave created by a pebble dropping into water, travelling through the same slit. The wave will spread out from the ends of the slit. Light shows similar behaviour. Read about Huygen's principles to learn more
There is an absolute inverse relationship between the diameter of the aperture and diffraction. So, with a smaller sensor, diffraction is a problem at lower f numbers. This is because the final viewed image is more magnified from the image on the sensor. Also, with smaller, high megapixel sensors, the cells are smaller and the diffraction is relatively larger. With my 4/3 sensor diffraction becomes noticeable at f8.
You really should look up how the angular resolution work. Many people don’t understand that a given photon enters the camera through the whole aperture
I love this stuff, from my past life it's what I spent a lot of time engaged in. On a fundamental level it really does come down to Heisenberg's Uncertainty principle. In short the more you squeeze a particle/wave (Wave-particle duality), the more it tends to spread out. It can be very counter intuitive. Fundamentally it comes down to Field Theory (It's the Waves that do the talking). Reach out and try and grab some waves, they won't be tamed. Photography really comes down to painting with light and the digital technology available today and where it's moving. The future of this technology opens up creativity on a whole new level. Tony, I really appreciate these interludes into the more technical aspects. Your wife is pretty cool to. Between the two of you, it open up an array of topics. Thanks again.
Light oscillates in terms of the electric and magnetic field strengths, however, this is not actually a change in position transverse to the direction of the photons. Therefore, I doubt your explanation for the distribution of photons due to diffraction is correct. Note, I do agree the photons do spread out; I just don't agree with your reasoning for why. More likely is that pixel photo-sites on modern sensors are so small that the diffraction (normally only noticed when the aperture is of a comparative order of magnitude to the wavelength of light) is still visible even with the difference in size of the wavelengths and the aperture of cameras.
Oscillations in the electric and magnetic fields could certainly cause differences in how the photons interact with nearby particles that they pass. The phase of the fields would determine how much and in what direction the photon will be deflected. Differences in wave phase between photons of the same frequency and on the same path would cause the smearing that Tony is talking about.
Dear Tony, I like your videos, especially the more technical ones about crop factor and so on, but your ideas about physics are confused at best. I say that as a physicist just coming home from doing a diffraction imaging experiment. Forget all about quantum physics and photons, that is really not relevant to the discussion of lenses. You must think in terms of wave optics. Google for terms like Abbe diffraction limit and Airy disk. Once you have understood the numerical aperture in the Abbe diffraction limit you can understand everything from photography, microscopy, telescopes up to why the Event Horizon telescope needed to synchronize radio telescopes in Greenland and on the South Pole to take an image of a black hole. Such as of now, all your practical implications for photography are correct, but your physical explanations are bogus.
First of all I'm no expert in this subject but here's what I understand of light and diffraction and why it does what it does. Light is both a particle and a wave depending on what qualities are tested. Diffraction is a wave property and therefore light being bent has absolutely nothing to do with electrons in. This can be demonstrated with water also. You can think of parts of wave being the own beginning of a wave. This means that to keep a wave-front straight you have to have constant waves on either side to keep it moving in the desired direction. You can demonstrate this by filling your sink with water and poking the surface with a finger. You'll see that a spherical wave forms from your finger's movement. Now if you stick your hand in with 4 fingers you'll see that you get two straight waves parallel to your fingers. This happens because the energy from the 4 fingers cancels out the wave's movement in all but the waves' mutually agreed direction. So the energy moving from your index finger to your middle finger cancels out by the energy from your middle finger moving towards your index finger. If you were to remove some of those balancing forces it would mean that the energy carrying on sideways in the wave becomes free to move sideways causing the wave to "bend" or "spread" in the direction it wishes. This is what happens near the aperture blade and causes the curvature in light making the images not as sharp. This phenomenon is magnified at smaller apertures due to the fact that a bigger portion of the light comes from near an edge where this "counter-balancing" is cut off by the blades and the wave is allowed to bend freely in the direction it wishes.
This is a well understood phenomena. The comparison of light as wave is correct as opposed to the explation. The amount of light bending near edge is due to wave property. Eventhough the aprature is 5000 times the wavelength. Because the bending and bluring due to defraction is less as few pixel. Which is v less bending but is enough to make the image soft.
Wow - who knew you had so many physicists tuning in Tony? As just a simple photographer I like to have reasonable understanding of the more technical aspects, but when you need 25 physicists debating theories I decide it's enough for me to know that diffraction occurs and I therefore endeavor to shoot as near my lens' sweet spot as possible. Love all that physics tho! :)
Hi Tony. Physicist building instrument for astrophysics. Your scientific description is unfortunately all wrong. I am not sure where you get these informations, I have the feeling that it was a simple guesses: - "Photon attracted by electrons on the border" ?????? Where did you read such thing ??? - "Photon traveling not straight but going up and down in a wave pattern" ??? This is a total confusion of the so called wave-particle duality which is more a representation problem and has been solved by quantum mechanics since 70 years. What you can say is that their is no mentally, or by draws, satisfying way to represent what is a photon (or any particle in the macro world), some time it is better to represent light as particles bullets some time better to represent it as waves, like water waves (depend of what you want to show). But they are just representation or mathematical tricks. The best way to approach the problem, closest to reality, is to talk about probability. But no photon are not traveling as you drawn, not at all. - There is no meanings in what you drawn, each possible part of the object you photograph is emitting light in any direction and you cannot avoid to place an optical element (or a pin-hole) to form an image. They are many approach you could start with. And of course all are impossible to resume on a youtube comment. Maybe the best approach is to interview or ask a physicist, not to guess things. I am open for that or can orient you to any appropriate person in my lab with better communication skill than I have.
Really love all the comments. Tony I think you have unwittingly parachuted straight into the fundamentals of quantum physics. In "reality " you are attempting to describe probability graphically (which is impossible). I do think the more knowledgeable commenters should have cut you some slack..... your approach is extremely common and taught to our kids (eg graphic of an atom). This issue is well understood, just impossible to communicate in a non mathematical way. Besides your message is still 100% relevant from a photography perspective. Nice try mate!
Snapography this video indeed surprised me. So far I saw mainly simplifications from Tony contents which are totally fine even necessary. Sometime with mistakes perfectly forgivable. This video is kind of an invention presented as if it was a deep research of how light work. Quite disappointing and a bit scary when coming from somebody with millions of subscriber. Of course that is not so important here but what scares me is that I probably digest a lot of bs from this kind of channels i can trust on topics I do no know.
Sylvian I know what you mean. I've been doing aerial photography for years and watching Tony's videos on that subject is complete bs. It's a pity because you don't need to understand to get the photograhy message; no idea why tony didn't just acknowledge that and move on instead of dreaming up his own explanation
Yes. Fun fact: Diffraction in optical system is actually a "real-life" application of Heisenberg's uncertainty principle. The opening of a lens defines the position of a photon, which causes the an corresponding inaccuracy of the momentum of the photons and hence their direction, causing a blur.
Tony, you need to read more. Photons have no charge and no mass. They can however be influenced by gravity, which in short is a product of mass. Photons contrary to common sense operate like particles and like waves. Here's a suggestion. Short story: The macro scale analogy involves taking a bucket, fill it with water, toss a pebble into it and you'll waves. Now place a board with slits toss a pebble into said bucket and you'll see waves forming interference patterns, i.e. defraction, that is to say waves cancel and reinforce one another, as they pass through the slits. Abstract to small aperture photography light probably (after all it is quantum physics) forms similar interference patterns as it passes through a small aperture. As we used to say if you want to prove that, you'll need a bigger grant; if you want me to prove it get out your checkbook. If I explain more I'll have to add footnotes and a bibliography. One last remark, notice I did not bring the issue of wavelength, which for photography can be summarized as the ROYGBIV phenomenon.
Excellent video. Thank You. I was wondering why the pictures were coming out blurry in the background- when I decreased the aperture to f/20-22... Lens: Canon 85mm f/1.8. Mystery solved.
While the main point of Tony's video is valid. "Smaller apertures do increase the effects of diffraction" The explanation is kinda off. I think a some of the confusion is caused by confusing the physical phenomenons diffraction and interference. Diffraction is the bending of light at the edges of an obstacle (the aperture blades in this case) Interference is when light (or any other wave) can cancels itself out because of being out of phase with another other light. When people think of an diffraction pattern its actually an interference pattern that is caused by the diffraction of light allowing the light to interfere with itself at the plane of the sensor. Diffraction is is very well understood in wave mechanics via Huygens principle. The quantum mechanical description produces the same results so its generally not required to get into the quantum mechanical description.
Nerdhole alert, apologies in advance (I think that Tony & Chelsea's is the best photography channel on youtube - great scope, depth, balanced, generous, candid, honest).... The basic point that diffraction effects can degrade images when the aperture is small enough is right. So why would I ramble on? Too much time on my hands, that's why! (And I should probably have read for others who beat me to this.) I'm curious about who is saying that there is some confusion over diffraction. There is certainly interest in surface effects - what happens at the boundary between two materials, but that isn't the issue here. This is a problem of classical optics, much of which has been well understood for over 200 years. It cannot simply be electrons interfering with photons. Photons are massless and carry no charge, and the mass of the blades of the aperture is too small for mass-energy equivalence to play an observable role. But the real giveaway is that you can make a pinhole or slit out of any number of materials and see the same diffraction effects (assuming the pinhole or slit is of a constant size and quality and the materials are of equal thickness). In classical optics, diffraction is a product of the interference of waves. Classical optics is an approximation, but more than good enough at macroscopic scales. (Much the same phenomenon is at work with sound, which is why you can hear someone around a corner even when there is no surface for the sound to bounce off.) In quantum mechanics, particles also have wavelike properties, so you also see diffraction in quantum mechanics. One more nerdhole needle: There is a lot to be said for photographers understanding a little physics. For example, people used to go on and on about the superiority of semi-matte or matte finish displays over glossy. (I don't see much of this anymore, but maybe I'm just not paying attention.) The matte finish on a display is, in effect, a diffusion filter. It kills reflections, but it also degrades image quality. A little physics might also put to rest the cult of curved displays for HDTVs. Great for an imax or huge 70mm screen at a theater. Largely pointless even with a large screen at home (except to the extent that it also mitigates reflections).
When I first started product photography I had only a little knowledge of photography. I had to use a high F-stop to get larger products in full focus. So I had a huge issue with diffraction and aberration which led to a lot of time in Photoshop. Once I learned about focus stacking my images improved considerably. Thanks to Tony and Chelsea, Jared Polin, and other gurus on youtube, I have learned so much. Thanks, Tony & Chelsea.
There are two theories of light and both are correct even though one does not explain the other. The quantum theory and the classical wave theory. The quantum theory applies to light when it strikes an object, e.g. when light strikes the sensor. Quantum theory of light does not explain diffraction and diffraction does not explain quantum theory. The wave theory explains diffraction and is used where light travels from its source to another object as a wave, these waves explain diffraction. Diffraction is where the light waves of similar wavelength when passing through a small aperture will interact with each other, some waves will add to other waves and some waves will subtract at the aperture, what leaves the aperture will be something different. If you throw two or more stones into a pool at sufficient distance apart you will see the concentric circles interact with each other causing diffraction. Photons are electrically neutral so how would a electron attract a photon?
Just because you can't understand the physics doesn't mean that everyone doesn't understand the science. QED is one of the most detailed and well tested sciences that there is. Your attempt to use a photon as a particle, but photons have a duality, they are also waves. Diffraction is more of a wave effect. You have also not fully grasped the statistical nature of quantum effects. All together you just can't simplify these complex effects with your simplistic everyday experiences. If you want to understand what is going on do the math!
The interaction that causes Airy circles is a complex dance between the electromagnetic waves (photons) and the electric fields of the atoms and molecules that make up the material at the edges of the aperture. This interaction at the boundary is what leads to the diffraction of light. So you are correct in that regard.
Great article. What you are missing is the diffraction is affected differently by the medium that the particle is traveling through. The denser the medium, the more extreme the effect. Water is denser than glass, which is denser than air. So the light waves travel through the air and are slowed down by the glass, which causes bend. This bend is also affected by the tighter aperture, which applies more resistance or impendence to the light waves, which causes an acceleration effect due to the increases pressure.
Thanks as always! Your physics explanation is not quite right… the wave functions of light and diffraction through empty space and matter are well understood, just pretty complex. Photons are not “attracted to electrons”. All that said, the practical recommendations about how this should affect a real world shooter are spot on!
Wave theory and diffraction are well understood with near and far field approximation as well as computer aided lens design. And diffraction does NOT wreck sharpness, it is an inherent property of light, and depends on the wavelength and aperture size. It is like saying darkness wrecks image quality.
When you are talking about diffraction interference with a smaller aperture you should be be expressing the destructive interference as a wave not as a particle. Some mention of telecentric lens properties to mitigate this would be illuminating and germane. Conventional lenses have angular fields of view such that as the distance between the lens and object increases, the magnification decreases. This is how the human vision behaves, and contributes to our depth perception. This angular field of view results in parallax, also known as perspective error, which decreases accuracy, as the observed measurement of the vision system will change if the object is moved (even when remaining within the depth of field) due to the magnification change. Telecentric Lenses eliminate the parallax error characteristic of standard lenses by having a constant, non-angular field of view; at any distance from the lens, a Telecentric Lens will always have the same field of view. See Figure 1 for the difference between a on-telecentric and a telecentric field of view. Basically Telecentric lenses use the sweet spot of the sensor. The larger aperture of the "Nikon S Line" Z-mount are more telecentric than their F-mount brethren. Olympus went 4/thirds for this very reason, to increase the telecentric properties of their glass.
As far as I understand physics, diffraction is perfectly explained by quantum mechanics. It's exactly the same type of "self interference" as in double slit experiment, but instead of two slits you have a superposition of "infinite number of slits" with decreasing magnitudes the further you get from the central path of the photon.
Thanks, Tony. I was shooting a picture of a historical building in my town and I had this happen. The building had two towers like you would see in medieval times. I must have used F11 and the top of those towers curved inward. If that wasn't diffraction then it was caused for a different reason. I will try and go back to the site so I can shoot several at F8 and lower, then use F10 and up. Tried correcting this in my processing software to no avail. I will also try changing the focus point and see if it still happens.
Is is due to perspective as well as your lens distortion. Nothing to do with the aperture. You can correct this in some advanced retouch software such as DxO.
tony, your physical explanation is scientifically wrong. Please read up on diffraction again. There is NO ATTRACTION of the photons by the electrons at the edge of the iris. I don't know where you get that from. ... my background: optic/laser physicist ;-) the phenomenological explanation of it is alright though... for photographers. My recommendation is: Please don't seed fake news, it's better to simplily instead of coming up with non-truths :)
I agree, perhaps Tony should replace "attraction" by interaction. I wonder if the wave lights closer to the diaphragm experience a combination of mirage plus pinhole effects. I mean, some partial refraction trough the surface of the diaphragm with a low-pass filter.
Daniel Clarke: I think the Coanda effect is more like water tension, like the way water rolls around a soft radial edge ( like a rain gutter hood) until it’s mass causes it to fall. But then what do I know.🥴
A proposed subject for a tech-oriented explanatory video: Consider the actual measurement of the diameter of the aperture of fixed aperture zoom lenses in contrast to the actual diameters of the apertures of variable aperture zoom lenses. The definition of f-stop as f (which equals focal length of the lens) divided by the diameter of its opening (aperture) suggests that when a fixed aperture zoom lens is zoomed the actual measured diameter of the lens' aperture must be increased if the fixed value f-stop is to be maintained. Some definitions include mention of optics inside the lens modifying the effect of the actual measurable physical diameter of the aperture to produce a nominal equivalent diameter . It would be interesting to see just how much the measured diameter of the aperture of something like a 70-200mm f/2.8 lens changes when the focal length changes throughout its range, and to contrast that range of actual diameters with the changes in aperture diameter of a variable aperture zoom lens such as a 55-250mm f/4-5.6. If I understand correctly, the measurement of effective aperture changes of the fixed aperture zoom lens might actually be greater than those of the variable aperture zoom lens.
Most people believe that their lenses are sharpest around f8-f11 but most lenses are sharpest around f4-5.6. I think people believe this because shots taken at f8 are more likely to be relatively in-focus edge-to-edge and it's easy to confuse something that is slightly out of focus with something that isn't sharp.
That's silly, Tony. A photon has no electrical charge. Electrons should have no "pull" on a photon. Just imagine if we could bend light with magnets or static electricity!
@@meta4101 it's the basis of quantum mechanics that is needed here, which means dealing with wave equations when talking of photons and electrons. That's a whole lot different to electrodynamics, which is classical pre-quantisation model and really isn't appropriate at the quantum level. For that, you need quantum electrodynamics (QED) and it's clear that Tony is not familiar with that. It's not surprising, as that requires degree-level physics.
@@TheEulerID In a sense, all physics is qm. That said, diffraction is more easily explained classically than the 2-slit (self) interference of qm and was well understood in the 19th century as a wave property of light well before qm was devised in the 1920s.
Like some already mentioned, the science in this video is lacking a bit. The light behaves as a wave and a particle in the same time. In diffraction is the wave side of light that comes to play. The waves of light coming till the aperture are close to parallel, and once forced thru an aperture they take the curved shape due to the waves of light interfering with each other (not with the walls of the aperture). It's like looking at the waves formed in a lake by throwing a stone. Near the impact point, the waves look so round, but at a distance looking in the space of a few cm/in across, the waves look flat, parallel.
Tony , whilst I agree that diffraction ruins sharpness, your explanation may be misleading. There is no value in considering how photons are 'attracted' to the edge of the aperture, since diffraction will occur regardless of the properties of the material used. You could electrically charge the aperture to no avail. Diffraction is absolutely only dependent on the geometry of the aperture and is the result of the destructive and constructive interference of the light wave as it passes and bends through the circular diffraction slit, which in this case is the aperture. Diffraction can only be understood by considering the wave model of light, not the photon model, and that wave-particle duality of light is the conundrum of quantum mechanics. The diffraction pattern of the circular aperture is called the Airy disk, mathematically proven way back in 1835. Consider a point source of light in the object plane that has a single wavelength, this presents a wavefront to the aperture that results in a corresponding point on the image plane, but that imaged point will exhibit an Airy disk, albeit very small but bigger than the original point light source. The width of this Airy disk X is a function of the wavelength L, aperture f-number N, where X = 1.22 LN. NOW, consider that any scene we want to photograph is made up of essentially an array of point light sources, all of which produce an image at the image plane. We can consider these light sources as object pixels, so that each 'pixel' in the object plane corresponds to a pixel on the sensor image plane. The light's wavefront from each object pixel hits the whole aperture and results in an Airy disk at each sensor pixel in the image plane. At a certain aperture f-number and wavelength, the width X of the Airy disk can become bigger that the sensor pixel pitch, and hence you start getting smearing across pixels and a less sharp image. For example, at N=f/11 and L=420nm, X=4.6um, which can be bigger than the pixel pitch of many sensors. Given that the light from most scenes is a mix of colors and hence wavelengths, these wavelengths produce Airy disks of different diameters (similar to chromatic aberration), which produces additional smearing. Conventional optical approaches cannot get around diffraction, but I live in hope that the nonlinear approaches used in high-precision photolithography, used in making integrated circuits, will be adaptable to camera optics to minimise diffraction effects.
Enjoyed the video. The nitty gritty of knowing why diffraction happens is less important than knowing that it does, lets go take some pictures! Just finished a backyard bench test of my new Samyang AF 85mm f1.4 and I can clearly see flare and diffraction in action :o)
High frequencies difract less than low frequencies thats why sound diffracts around objects because it has a very long wave length from cm to many metres, whereas light wavelength is in nano metres so it does not diffract around objects it is blocked by objects.
Interesting and well-explained, thanks! I knew this phenomenon occurred from results from my photography, but I didn't know exactly why...I just kept away from higher f stops because photographers who mentored me over the years said the sharpest results are found around the "middle" of a given lens (maybe 5.6 or so)
I can't say what the physics are, but I thank you for bringing up this topic and giving us a nice simple mental picture that is sufficient to convey the effect and what photographers should do about it. I join you in asking those who know a more correct physics explanation to explain it as simply as you did. Just saying "Airy disk" fails the Fenyman test in that it provides knowledge of words without providing actual knowledge of the subject. So we don't need 500 people commenting with that, we just need the one who can explain the thing to a 6 year old (or an undergraduate). Until then I'll use your mental picture. Thanks for the video and please more such on technical subjects and practical photography techniques. Also, thanks to you and Skillshare for the 2 months free.
Folks below are waaaaay too caught up on the specifics required to understand this. I think your explanation for understanding the reasoning behind this is fine. An interesting way to prove the concept of waves bending would be to either watch a video on why the centre of a circular shadow is the brightest point (it's well trodden territory) or if you're at a large body of water just watch how waves interact with a solid pier or jetty. Glad I watched this either way as I hadn't put much thought into why diffraction occurs, this has helped a lot with picturing it in my mind and cemented it. Thanks Tony :)
Tony, I love this video. A great science communicator Brian Cox did his PHD in difractive scattering. While I am not a physicist I have always had a great yearning to know more about high level physics and came across his work a few years ago. It goes into a bit of depth about what you are talking a with photons interacting with electrons.
Well, it might mean that sensor size is not that important for landscape, since we would be limiting the amount of light on bigger sensors to a greater degree anyway, applying crop factor to aperture.
Diffraction is totally well-understood by physicist. It and the interference phenomena are taught in 1st year Physics at University or even earlier in some cases. You may check any 1st year Physics books for a good enough explanation. And forget your photon story. :) a discussion of the actual aperture size with respect to visible light wavelength would have made more sense.
Quantum physics has a principle called the Heisenberg uncertainty principle, which states that for any subatomic particle the more precisely you measure the change in position (I.E. the path a photon takes from the subject to the sensor) the less precise you can determine it’s momentum (I.e. to what degree the aperture blade will deflect the photon from a direct path straight to the sensor)
The light doesn't cross at the middle of the blades but at the middle of the lens. Some photons actually hit the side of the blades at angles and bounce of it. At the size of a photon the slice (side) of a blade is not thin at all. When the blades are wide open (f1.4) the angles of bouncing photons are more different and doesn't really affect the image at a fast shutter speed. they are more distributed on the sensor. But at f22 the angle of bounce is thinner and at a lowest speed it affect the image.
Seems to me it matters a LOT that you don't mention the role of the lens. Light reflected from a point in the scene diverges in all directions. A number of different pathways are available from that point to its image on the sensor. That's the job of the lens: to redirect the diverging photons into a convergent bundle that all hit the sensor at the same point. (You focus the lens to make sure the point of the convergent cone is right at the sensor, not further or closer.) Therefore not all photons travel the same distance, and not all of them pass equally close to the edge of the aperture/iris. If there is any kind of diversion of path of photons due to interaction with the iris of the lens, that will not be shared by photons which travel through a different part of the lens. Every part of the lens is simultaneously transmitting photons travelling in different directions, on their way from scene to sensor. All these different divergent cones of light are being turned into convergent cones of light by the lens. That is why larger aperture lenses are harder to make sharp: the cones are fatter and it's harder to make the edges of the lens and the centre of the lens focus on the same spot. As the aperture narrows, a higher proportion of the photons in a given cone will be passing close to edges of the iris, and the disturbance to their paths ("diffraction", if I'm right) will have more effect in introducing blur. Takehome: it's the difference between rays of light (photon paths) which are meant to get from a single point in scene to a single point on the retina, via different parts of the open lens surface, which is crucial. I don't think it's anything at all to do with different photons on the same path being out of phase with each other. If phase differences matter it will be because of the spread of paths and the disturbance of some, not others, by the edges of the iris. Den Rob
Photon path difference is only an issue if you have in-phase light to begin with. We photographers do not. The light path difference is entirely immaterial.
Top Rock Photography Fair enough except that one way of understanding light is that every photon travels by every available path and the result is a superimposition of effects. Feynman's way (in one of his popular works at least) of explaining diffraction effects involves discussing which pairs of paths are in phase, which out of phase, with each other, on arrival (of the same photon by many paths). Where there is destructive interference you get less light, where positive you get more light, the result is the various diffraction patterns you see. Diffraction of light either needs to be explained using the pretence that it's all waves, or else by reference to photons. Explaining why these particles produce wave-like effects requires quantum theory, which as another commentator has said, is err, not easy, mathematics.
@@denisrobinson8504 Fine for a double slit experiment, where we first send the light through a single slit to approximate one wave, then through a double slit. The double slit experiment does not work when there are two or more independent waves moving towards two disparate slits, into a common area. One photon coming close to the top edge of the aperture blade, can be treated as several photons moving in-phase in several directions from there, but a different photon coming close to the bottom of the aperture blade, will not cause a diffraction pattern which will interfere with the photon on the top in a predictable manner. If the photon at the top was the same photon at the bottom, then that would be an entirely different thing. [EDIT] To clarify, it works for a point source of light. When speaking of an image made from reflected light, (with or without sub-surface scattering, etc.), then we no longer get a homogeneous point source of light. Particularly true when their is another point source of light right beside it. It is the distance between two point sources of light increasing, and diffracting through an iris, which gives us the cone of confusion, or rather, the angle of the arc of the cone of confusion, which tells us how to get things sharp. By looking at that, we see that the entire interference thing breaks down when we are speaking of multiple light sources, and even more when they are not homogeneous, as when we have SSS and even multiple sources of light reflecting off of a single point. (Bear in mind, that I am speaking of the interference thing breaking down, not the diffraction thing. Diffraction is still real, and still causes non-sharp images, and loss of detail). To put it another way, when the difference in light path is on magnitude of λ, whee λ is the wavelength of the light, we can see a distinct interference pattern from the diffraction. As the path difference becomes of much higher magnitude, the interference pattern becomes less distinct, turning into an indistinct, graduated, blur, (even with a point light source of homogeneous light, and perfectly aligned circular aperture). So diffraction plays a greater role, interference plays no significant role at all. [/EDIT]
I usually don't shoot wide open, and if I accept that it might not be the most perfect. Whatever is needed for the situation right? Nor do I shoot at F22, unless yes there is Macro. Is there a loss of sharpness at F22? Yeah even with a nice big sensor and nice big "pixels", there are still limits to how things work. But a slightly blurry but artistically good looking shot, or a super sharp shot but only a little slice? That is the question.
Skillshare online learning is great, but problem with online catalogues and memberships is that they can be taken away at any time. Let's say I comment on a video and YT doesnt like my comment. They have the ability to wipe my history out, blacklist me, ghost my account etc. Same with Amazon, FB and the lot. I like physical books because you don't have 'big brother' watching your every move.
Tony, the variation in the distance from the edge of the aperture is a function of the role of the lens elements. Different paths of light from the subject are focused back on the sensor by the lens elements. There are different route to get to the sensor through the lens and these paths are all different distances from the edge of the aperture blades. This will have a far larger effect than the differences in the wave. That might only be an issue with a pinhole camera. If you included the elements in your diagrams and showed the paths from one point on the subject to one on the sensor, you would illustrate the issue better.
When you use small aperture, some light may be reflected by the aperture blade itself and make some disturbance in the are between lens and aperture blade. Different color of light have diffrent wave length and they bended differently when passing throgh the glass.
Tony great video. When light from a subject arrives at the sensor after passing through a thin slit (the closed down aperture) it does so half a wavelength out of phase with the light leaving the middle of the slit. These two rays interfere destructively. In other words, the light from one half of the opening cancels out the light from the other half. The rays are half a wavelength out of phase because of the extra path length traveled by one ray... I think.
Prediction: Ken Wheeler is going to pretend that he cant talk because hes laughing too hard. He is then going to say that you dont know any of what youre talking about and then something about magnetism....
DanSchwegler I can’t take Ken Wheeler serious because I’ve never seen his work: he talks the talk, but I can’t seem to find any portfolios of work other than some basic snapshots he puts on Instagram here and there.
If you've addressed this previously, I'd love a link, but this video made me think of something I deal with at times - chromatic aberrations. I shoot A LOT in the winter (in Alaska ~8 mos a year) and have found ways to deal with most issues. But I do like to use a prime lens at times (i.e. 35mm or 50mm @f1.8 or f1.4) when it is dark to get the most light possible when shooting things such as sled dog teams. Flash is prohibited in most of these situations. Anything you can contribute to getting the best images, of moving subjects, in near total darkness, without (or minimizing) chromatic aberrations, would be fantastic.
Very well made video. Thank you Tony. A humble request: Please make a video on WHAT IS FOCUSING? What it means for an object to be in focus? How lenses change focus? And what exactly changes in lenses in order to change focus from one point to the other? I have searched for this a lot but still don't have a good answer. I would be grateful if you could explain it. PS Viewers also please reply if you have an explanation.
Tony and Chelsea, I love your videos talking about various cameras. But, I feel that the best investment that a new photographer can make is purchasing your books. Beginners are not going to be happy with their photos until they learn the basics in my opinion. You two tell it like it is, and give invaluable advice. Thank you for all that you do!
As much as I like your videos on photography, the physics teacher inside me has to say this: we know perfectly why diffraction happens. By the way, there is no "attraction" between the photos and the electrons in the diaphragm.
Probably not electrons. If you look at the edge of a desk or counter with good contrast behind it you can see light being lensed around the edge. Most shutters are a denser material than air and as such they attract the closest atoms of air closer to the surface of the edge such as surface tension in water. The denser something is the more it bends light and as the air molecules are denser near the edge, hence more lensing. In graduate level physics "optics" we learn that photons are electromagnetic waves. Though more advanced classes look at the true aspect of the photon since that graph that we study actually spins 360 deg for each wavelength. (This is not bragged about since the spin would ruin the explanation for polarization) So, if it was electrons then you would have scattering in more of a Fraunhofer diffraction pattern.
I forgot to note that the lensing only goes out 10 to 15 atoms, it is hardly noticeable unless you are a camera nerd with 36 MP or better. PS I once took wedding photos of the rings and got too sharp. Every hair, every skin flake, and every grain of dirt, and there wasn't a softening software that could pull it out. 55mm 3.5 micro Nikon it matches sharpest Nikon lens made, Oops.
Some of the loss of sharpness at a wide open aperture is due to the difference in the distance traveled by two light particles from the same source: one thru the center of the lens, the other at the edge. The light at the edge travels a slightly longer distance than the light passing thru the center. When this difference approaches the wavelength of light, you get wave interference...
I think just the reflection from the edges. Also a small aperture amplifies the errors in the glass surface that would be otherwise canceled out with open aperture. Also there are lenses that have very minimal diffraction even on F22
This effect has been proven by one of my students in the lab who purposely wanted to exploit this effect bending light to measure its component parts via a slit made from two close razor blades. It did act like a prism and also bending the white component part light. Unfortunately the previous effect wasn't investigated further.
Diffraction was always a function of Focal Length. I shot on 11-14 and 8-10 cameras. We had to use F 90 and F 132 with big bulbs. I always used at least 2 stops down. I found that I could not use f 16 on Macro 4/3 Macro Best results where at 1 stop down from wide open. Full frame Nikon lenses would handle 16 but not 22 without serious degradation. Hasselblad lenses always seemed best wide open. But times change.
I often enjoy the videos on this channel. I must echo other comments about the incorrect scientific explanation here. I suggest looking up the wave particle duality and the DeBroglie wavelength. As you mentioned the double slit experiments, that is important here. Depending upon the wavelength, there is a size of an opening at which diffraction occurs. Light passing through a smaller aperture perpendicular to the opening will not suffer from diffraction. As the angle of light approaches the plane of the aperture, it effectively makes the opening act as though it’s smaller - small enough to cause diffraction. Short version: smaller openings means light off axis from the normal to the plane of the opening have less wiggle room to be off axis.
My Fuji 10-24 at f/22 is so horrible, diffraction is so bad it looks like its out of focus. Open it up to f/8-f/11 and it is just mind blowingly sharp. I hope Bryan Peterson's 4th edition of Understanding Exposure corrects his statement on diffraction because in his 3rd edition that I have he said it doesn't matter, maybe in the early 2000s and the 12mp sensor he was using. But now with crazy high megapixel sensors and high resolution displays...it very much does matter now.
Let's just say the light near the iris edge "trips" over it. Not scientific but sufficient for a photographer's needs. I generally try to stop down at least 2 stops from wide open but not beyond about f11. Generally I prefer a bit of blur with things in the foreground with landscapes. Macro often requires f22 or f32 to get adequate depth of field.
In 1982 I bought a Tokina 35-105 lens. It was advertised as the first computer designed lens. The color images were always muddy. With a magnifying glass I could see color separation. It was like I'd stacked 3 images, each with a very slight offset. It happened at all f-stops. It was either a bad design or poor coatings. I gave the lens away and used nothing but fixed lenses for decades.
I believe Nikon was using a computer to help design lenses somewhere around 1970. Something I remember reading when reading the history of Nippon or Nikkor lenses. JFYI
I think Tokina was being a bit loose with their advertising there. The 1974 Vivitar Series 1 70-210mm f/3.5 Macro Focusing Zoom had its optical elements computer designed by Opcon Associates, and from research it appears that electronic computers were being used back in the 1960s. That's not surprising as prior to that it took a lot of human computers to do the calculations.
Are light waves affected as they pass through glass? Camera lenses are comprised of many lenses. Perhaps light waves traversing many glass elements are tweaked off their original paths thus softening the image? With this in mind, I usually set my stops around F8 as a safe average. This seems to be an average sweet spot for most lenses. Cheers.
Doh, that's what the glass is for!!! The light MUST be bent off its original path. All over the lens surface, light waves are being bent in the hope of bringing the right clusters of them together at the right points on the sensor.
Thank you for a good explanation. I remember with our small-sensor video cameras around 2010, using the built-in ND filters are so necessary. Without it, not just soft - so soft the footage was useless.
Always thought that diffraction, through any medium at any scale was a result of Huygen's principle. Looking forward to a follow up. Thanks for all the great videos!
It makes sense that the light rays from differing angles from same field of view, having to pass through a smaller aperture, will interact with each other more in a asynchronous manner.
How does a camera know that what it's looking at is 3 dimensional, and that tree X on the other side of the lake is 150 feet away, while tree Y is 220 feet away? I don't understand why depth of field exists at all, and no I have not even bothered to research it. From the camera's point of view, it should see a flat environment and everything is equally in or out of focus.
Well, your thought on how the photons interact with the aperture wall are not quite right. It's not like they're out of sync and some get "closer" because their wave peaks are closer to the wall than others. What happens is that photons do act like waves, waves that interact with the particles in the aperture. This is a quantum-mechanical effect, but it can be thought of just fine at these scales are macro-scale waves (like water waves). Some of those photons pass closer, and they get diffracted more, some are further and get diffracted less. So you get a spread because of that. Overall I'd say that this is very well understood by modern physics.
I don't know, but wonder, how much optical companies have experimented with the edge of aperture blades to affect diffraction. If we consider diffraction in photography to occur as it passes the edge of the aperture, what occurs to diffracted light as it is refracted by at least 2 to perhaps 8 glass elements after?
Probably the aperture is close enough in thinness to come close to the wavelength of the light, thus bending it around (similar to why we hear sound around corners, but don't see). The same effect is responsible for why leaded glass is translucent but still holds off a massive amount of x/gamma radiation. An interesting experiment would be to see whether the amount of diffraction differs between shots dominated by different colors of light. Some should be deflected easier than others.
The size of the diffraction spot on a focal plan dépend more or less of the f-number, the larger the f-number the larger is the diffraction pattern (google airy disk). A f/22 lens will have a diffraction spot twice larger than a f/11. However it’s proportion to the picture (the sensor) will be the same when comparing a f/22 on a ff and a f/11 on a M43.
Hi what camera and lens are you using for your tests? I haven't tested what Tony is talking about and I'm somewhat new to still photography and I recently bought a Panasonic GH5 and using Panasonic vario 12mm to 60mm lens and a Panasonic vario 45mm to 175mm lens.
RockstarBruski Hi, Most of the time I use panasonic G9 with kit lens panasonic Leica 12 60, I heard great stuff about GH5 in photography too, however, as Tony said, there is a lot of factors that affect sharpness but getting a decent lens like the panasonic leica is a good start.
I would put it out to Dianna Cowern aka PhysicsGirl. She's clearly loves optics and lasers, and since she has a physics background I think she could approach this subject more intuitively.
It's simply planar waves and obstacles (in this case, the lens frame or the aperture). The larger the diameter of the front lens, the better the (theoretical) resolution. Just see astronomy, there you have nice explanations about airy discs, size of main disc and light distribution in harmonic (diffracted) discs. Finite optics will never generate a point picture from a point source. You will always end up with a Fresnel distribution of light. The more you stop down (higher f-stop), the more you will see diffraction. There is no secret about this issue. Ok, one might argue about the contrast (or ligt intensity) of the main disc in comparison to the spurious ones…. By the way… light is known to be a longitudinal wave… what you draw is transversal… big difference :-)
Let's call it the Northrup theory of diffraction since it is different than existing scientific theories of diffraction. The hardest part to defend will be the aperture edge electrons pulling the incoming photons onto a different path. Electrons have a negative charge but photons have no electric charge.
Dude! Totally get you are shooting in your kitchen, can you please lav mic or have a close shotgun in the future for these. The sound is absolutely killing me!
First 500 get a 2-month free trial to Skillshare: skl.sh/northrup13
Tony, What's with the sound. Your voice is sounding thin. Mic? Post processing? Just not as good as the studio mix!
Tony - What happens, with regards to diffraction, when I put a 2x extender on my 300mm f2.8 lens? I realize that I'm shooting at F5.6, losing 2 stops, but does diffraction come into affect quicker, or differently, because of the 2-stop loss?
@@sfink16 I take it the 300/2.8 is a prime of some sort. At 5.6 the diffraction should still be ok. Most of the time it becomes noticeable after F11 and up.
Shashank Singh What "corners" are you referring to? My apertures are almost round; they don't have no stinkin corners.
Take down this video, Tony. Everything you say is false. It's about time to establish quality control.
Tony - diffraction occurs for any wave that travels through a slit no matter the size, given by a specific math formula. For a circular (or close to it in terms of relative differences) aperture this creates a diffraction pattern known as an Airy disc and described by the approximate formula sin(x) = 1.22*(wavelength/diameter) where x is the angle of first minimum, and is often used as the size of the disc (in reality a bit more complicated). The reason softness occurs due to diffraction is if the Airy disc is larger than the pixels receiving the information, because it can no longer distinguish two point sources cleanly. The aperture at which this occurs is known as the diffraction limited aperture, which is the largest aperture at which the Airy disc is so much bigger than the pixels size of the sensor that two point sources start overlapping the pixels that record them. Usually we use 2-3 (the popular online calculator uses 2.5) pixel sizes for which there will be softening. In the camera world the previous formula can be further approximated by x = 2 * 1.22 * wavelength * Fnumber. Using 525nm (green, assuming everything is corrected to this wavelength as a simplication) and f16 you get 20 microns. A 5d4 has a pixel size of 5.36 microns and a 7d2 has a pixel size of 4.1 microns so both would see the soften effects of diffraction. In reality with Bayer sensors you have more green pixels so they would technically hit DLA sooner. Note this formula assumes 100% pixel peeing at typical computer distances. As that is relaxed the DLA increases.
Thanks for a clearly expressed method to calculate diffraction... more useful to photographers than the underlying theory - which at some level always becomes "because it does" to anyone.
I AM a physicist. And the explanations below about Airy circles are correct. The f/stop diffraction has nothing to do with sides of aperture. The best way i can explain it to the photographers is that passing light through an aperture turns that light from hard to soft. The effect is allot more pronounced when size of aperture is close to wavelength of light; but the effect is there for all apertures and all wavelengths. Explanation by Antonio Sanchez in the comments is correct. Also, making smaller pixels does not make diffraction worse; it enables you to see blur from diffraction better.
A physicist huh? We are all super impressed. You should use that big ole brain that perfectly understands diffraction to figure out the difference between a lot and allot.
@@kronk358 are you being a Dick?
Because you kind of sound like a Dick. I am happy that he took the time to explain this mo better
@@kronk358 That post was uncalled for. The ability to spell has nothing to do with intelligence and a knowledge of physics.
@@nyobunknown6983 oh relax Francis, it was funny.
While the practical meaning of your video is right, the science or your guesses are quite off. Diffraction has long been understood, it is just damn complex math if you want all to be right, similar to semiconductor theory, a mess if you want to calculate stuff. Some other commenters already pointed out useful resources for the correct info. Love the community!
Physicist here:
Single slits also produce diffraction, of the same kind as the double slit experiment. It will produce two things, first of all an interference pattern, where you see concentric circles, dark and light. Second, the light will be diffused from the straight path and will travel in all directions, although most of it will be concentrated along the original path.
There is a characteristic angle that measures the size of these effects, and it is given by the wavelength of the light (around 500 nm) divided by the size of the slit (around 2mm), so about 0.00025 radians. This is a very small angle, but it is about angular size of the pixels of your camera as seen from the diafragm of your lens. So you will see these effects on your camera. I dont do optics, but it should possible to put concrete numbers on these effects (e.g. the angle to the first destructive interference, or the angle that contains 90% of the energy)
It seems like if you're willing to make the sensor larger, you could keep your apertures larger, and it would improve the *angular* effect.
Is the slit creating a bandlimited impulse or somesuch like you'd see in a 1d bandlimited signal? Would a (spatial) low pass filter prevent some of the interference (just as a low pass filter prevents aliasing in a bandlimited signal)?
@@microcolonel But then you would decrease your DOF, I am not sure if there is some optical trick to overcome diffraction and obtain a photo with the same DOF. Maybe it is possible to remove most of it computationally. In any case, the advantages of having most of your subject in focus for macro photography outweighs the resolution loss due to diffraction.
I am a Physics student at Purdue University (not a grad student or a professor, but I am graduating soon). Stopping down the lens still uses all the lens. The difference is that light coming in at more extreme angles (through the edges of the lens) are removed by the aperture. That removal of high incident angle light makes the focus point sharper because the centers of lenses are generally free of aberrations (the edges are much harder to get perfect). In laser laboratories, it is not uncommon to shoot the laser through the center of a large and cheap lens rather than through a small and expensive achromatic lens (the centers of lenses generally don't produce the same amount of chromatic aberrations). The reason that I say that the whole lens is still used is because the whole scene is still visible. Using less of the overall glass would be the same as masking (note that mirror lenses behave differently to masking, there it is more like an aperture (personal experience)). The blur from high f-numbers is most similar to the "knife edge diffraction." The light does interact with itself and the pattern can be seen in water (Huygens's principle).
So, no matter what my camera or lens is, the first thing to do as a landscape shooter is to stack in a steady environment could be inside or out outside and take a series of photos to each F/STOP and check where the lens sweet sharp F/STOP is and I will do this on infinity focus because that's what I do most of the time.
In my physics lecture it was quiet a bit different, but yeah... Why did'nt you just ask a physics youtuber for help/collaboration?
or attended a physics lectures in school))
Rule of thumb - if your lens goes to F22 dont go over (halfway) F11 or if lens maximum is F16 dont go over F8. It would be a good test whether ND filter is worse image quality than lens diffraction for long exposures
Great topic. I’m an electrical engineer and astrophotographer (with telescopes), not an optical physicist. But the math for diffraction is pretty darn simple on a basic level. Instead of talking about aperture as a focal ratio, it is simpler to talk about it as a diameter or radius, r, of the physical aperture. Light near the edge of the aperture is bent. Light away from the edges in not. So just look at the ratio of the aperture edge (bent light) to aperture area (unbent light). Edge = Circumference is C=2*pi*r. Area is A=pi*r^2. C/A = (2*pi*r)/(pi*r*r) = 2/r. So diffraction is inversely proportional to aperture radius. Also, not sure about those waves - maybe a secondary effect? But as a first effect, some photons are nearer to edge than others, so they get bent more. Some are in middle of aperture and don’t get bent. Others are at the opposite edge of aperture, and get bent the opposite way. That is why the light scatters and an image point becomes distributed (i.e. blurry). We can call this the airy disk. This is essentially the single-slit experiment. If the single slit (aperture) becomes small enough to approach the wavelength of light, the diffraction rings show more strongly. If we have a longer focal length, then we magnify it more and it is easier to see (or it spans more pixels so the sensor can resolve it). Another point on shooting through glass (especially thick aquarium glass): a big aperture collect light that passes through a bigger area of the glass, so you see the variation across the glass. Telescopes through windows are very bad. My Fuji APS with 56mm f/1.2 is very bad at the aquarium. My iPhone with tiny sensor and tiny aperture radius is very good through the aquarium glass because the thick glass doesn’t vary much across the tiny couple of millimeters of aperture. Essentially, cheap glass is the same issue as lens aberration, only worse.
Diffraction can be explained by Hygens principal because light behaves as both a wave and a particle. Check out the video about light by crash course.
Toby Bass Videos about quantum physics are helpful too. It sounds really unintuitive that the photons “know” the gap is small and have to have a less precise position, but that’s just how it works at that scale.
@@Ty4ons You don't really need QM for this. The math was done in the mid to late 1600s. The only tricky part is understanding the limits for diffraction to occur. He seems to think that light is a particle in his explanation (he acknowledged the wave nature but doesn't quite internalize it). The best explanation is the diffraction caused by a razor blade.
If you think huygens principle actually explains why diffraction occurs, you are missing the point. No one actually knows.
@@markevely1583 what is the point im missing? Seems pretty believable to me
@@tobylukebass6234 it is not about 'belief' it is about the physics and understanding a very simple point, no one actually understands why diffraction happens. Lookup the double split experiment , plenty of UA-cam other material. Huygens is just away of thinking about it not actually what happens. Or read QED by Richard Feynman then say you understand the subject.
I'm not a physicist myself, but I think this is all well-understood. And it is not to do with electrons in the iris attracting photons. It is just a result of the wave nature of light. You can see the same effect on waves on the surface of water, for example. The light bends around apertures as would any wave. Light at the aperture acts as a wave front, resulting in the light spreading out.
So what Tony says at 7 minutes then?
@@wallcrawler62 ... is TOTALLY incorrect
oh, no, Tony is wrong? again? and again ..
It takes supermassive objects to bend light...
...or the aperture of a DSLR.
Tony knows! xDDD
Technically, diffraction happens at all scales with all waves, and it's just that the significance it has is smaller as the size of the aperture gets larger relative to the wavelength. The thing about photons traveling as waves is a bit off, though you mention phase differences, there are also wavelength differences. Even so, diffraction still happens with coherent monochromatic light -- you can diffract research-grade lasers, for instance. The behavior at the photon level is largely statistical, and the wave behavior is the statistical distribution that follows the pattern of that wavefront. The general fit for the behavior at the aggregate scale is basically a Fourier Transform of the aperture shape. This is the model we also use to simulate not just lens aperture bokeh, but even things like glare as perceived through one's own eye. Of course, in practice, this is compounded by the fact that you anyway have some variance caused by passing through glass on the way to the aperture, and then more again after.
To be exact, the Fourier Transform is basically equivalent to Fraunhofer diffraction, and technically Fresnel diffraction is more correct (and appropriate for things like glare through the eye), but the significance of the Fresnel component at far field distances -- and the distance between a lens aperture and the camera sensor would qualify as "far" in this scope -- is basically zero, so it just reduces to Fraunhofer diffraction.
Diffraction is actually a fairly fundamental phenomena shown by light and can easily be understood using the wave theory of light. Basically in order to understand it, think of light as a wave. Imagine a wave created by a pebble dropping into water, travelling through the same slit. The wave will spread out from the ends of the slit. Light shows similar behaviour. Read about Huygen's principles to learn more
Watch the video; I address this
Yeah but your claim that scientists don't understand it is incorrect, it was understood in the early twentieth century
There is an absolute inverse relationship between the diameter of the aperture and diffraction. So, with a smaller sensor, diffraction is a problem at lower f numbers. This is because the final viewed image is more magnified from the image on the sensor. Also, with smaller, high megapixel sensors, the cells are smaller and the diffraction is relatively larger. With my 4/3 sensor diffraction becomes noticeable at f8.
You really should look up how the angular resolution work.
Many people don’t understand that a given photon enters the camera through the whole aperture
I love this stuff, from my past life it's what I spent a lot of time engaged in. On a fundamental level it really does come down to Heisenberg's Uncertainty principle. In short the more you squeeze a particle/wave (Wave-particle duality), the more it tends to spread out. It can be very counter intuitive. Fundamentally it comes down to Field Theory (It's the Waves that do the talking). Reach out and try and grab some waves, they won't be tamed. Photography really comes down to painting with light and the digital technology available today and where it's moving. The future of this technology opens up creativity on a whole new level. Tony, I really appreciate these interludes into the more technical aspects. Your wife is pretty cool to. Between the two of you, it open up an array of topics. Thanks again.
K man...
Light oscillates in terms of the electric and magnetic field strengths, however, this is not actually a change in position transverse to the direction of the photons. Therefore, I doubt your explanation for the distribution of photons due to diffraction is correct. Note, I do agree the photons do spread out; I just don't agree with your reasoning for why.
More likely is that pixel photo-sites on modern sensors are so small that the diffraction (normally only noticed when the aperture is of a comparative order of magnitude to the wavelength of light) is still visible even with the difference in size of the wavelengths and the aperture of cameras.
Oscillations in the electric and magnetic fields could certainly cause differences in how the photons interact with nearby particles that they pass. The phase of the fields would determine how much and in what direction the photon will be deflected. Differences in wave phase between photons of the same frequency and on the same path would cause the smearing that Tony is talking about.
The slit experiments and the wave propagation examples are the same as this phenomenon.
It depends on if they're Nikon or Canon electrons 🤹♂️🤣
The most creative comment hahaha!!!
😎👍😂
them canon electrons are no damn good i tell ya
Dear Tony,
I like your videos, especially the more technical ones about crop factor and so on, but your ideas about physics are confused at best. I say that as a physicist just coming home from doing a diffraction imaging experiment. Forget all about quantum physics and photons, that is really not relevant to the discussion of lenses. You must think in terms of wave optics. Google for terms like Abbe diffraction limit and Airy disk. Once you have understood the numerical aperture in the Abbe diffraction limit you can understand everything from photography, microscopy, telescopes up to why the Event Horizon telescope needed to synchronize radio telescopes in Greenland and on the South Pole to take an image of a black hole.
Such as of now, all your practical implications for photography are correct, but your physical explanations are bogus.
First of all I'm no expert in this subject but here's what I understand of light and diffraction and why it does what it does.
Light is both a particle and a wave depending on what qualities are tested. Diffraction is a wave property and therefore light being bent has absolutely nothing to do with electrons in. This can be demonstrated with water also. You can think of parts of wave being the own beginning of a wave. This means that to keep a wave-front straight you have to have constant waves on either side to keep it moving in the desired direction.
You can demonstrate this by filling your sink with water and poking the surface with a finger. You'll see that a spherical wave forms from your finger's movement. Now if you stick your hand in with 4 fingers you'll see that you get two straight waves parallel to your fingers. This happens because the energy from the 4 fingers cancels out the wave's movement in all but the waves' mutually agreed direction. So the energy moving from your index finger to your middle finger cancels out by the energy from your middle finger moving towards your index finger. If you were to remove some of those balancing forces it would mean that the energy carrying on sideways in the wave becomes free to move sideways causing the wave to "bend" or "spread" in the direction it wishes. This is what happens near the aperture blade and causes the curvature in light making the images not as sharp. This phenomenon is magnified at smaller apertures due to the fact that a bigger portion of the light comes from near an edge where this "counter-balancing" is cut off by the blades and the wave is allowed to bend freely in the direction it wishes.
This is a well understood phenomena. The comparison of light as wave is correct as opposed to the explation. The amount of light bending near edge is due to wave property. Eventhough the aprature is 5000 times the wavelength. Because the bending and bluring due to defraction is less as few pixel. Which is v less bending but is enough to make the image soft.
Wow - who knew you had so many physicists tuning in Tony? As just a simple photographer I like to have reasonable understanding of the more technical aspects, but when you need 25 physicists debating theories I decide it's enough for me to know that diffraction occurs and I therefore endeavor to shoot as near my lens' sweet spot as possible. Love all that physics tho! :)
Hi Tony. Physicist building instrument for astrophysics. Your scientific description is unfortunately all wrong. I am not sure where you get these informations, I have the feeling that it was a simple guesses:
- "Photon attracted by electrons on the border" ?????? Where did you read such thing ???
- "Photon traveling not straight but going up and down in a wave pattern" ??? This is a total confusion of the so called wave-particle duality which is more a representation problem and has been solved by quantum mechanics since 70 years. What you can say is that their is no mentally, or by draws, satisfying way to represent what is a photon (or any particle in the macro world), some time it is better to represent light as particles bullets some time better to represent it as waves, like water waves (depend of what you want to show). But they are just representation or mathematical tricks. The best way to approach the problem, closest to reality, is to talk about probability. But no photon are not traveling as you drawn, not at all.
- There is no meanings in what you drawn, each possible part of the object you photograph is emitting light in any direction and you cannot avoid to place an optical element (or a pin-hole) to form an image.
They are many approach you could start with. And of course all are impossible to resume on a youtube comment. Maybe the best approach is to interview or ask a physicist, not to guess things. I am open for that or can orient you to any appropriate person in my lab with better communication skill than I have.
Really love all the comments. Tony I think you have unwittingly parachuted straight into the fundamentals of quantum physics. In "reality " you are attempting to describe probability graphically (which is impossible). I do think the more knowledgeable commenters should have cut you some slack..... your approach is extremely common and taught to our kids (eg graphic of an atom). This issue is well understood, just impossible to communicate in a non mathematical way. Besides your message is still 100% relevant from a photography perspective. Nice try mate!
Snapography this video indeed surprised me. So far I saw mainly simplifications from Tony contents which are totally fine even necessary. Sometime with mistakes perfectly forgivable. This video is kind of an invention presented as if it was a deep research of how light work. Quite disappointing and a bit scary when coming from somebody with millions of subscriber. Of course that is not so important here but what scares me is that I probably digest a lot of bs from this kind of channels i can trust on topics I do no know.
Sylvian I know what you mean. I've been doing aerial photography for years and watching Tony's videos on that subject is complete bs. It's a pity because you don't need to understand to get the photograhy message; no idea why tony didn't just acknowledge that and move on instead of dreaming up his own explanation
Yes. Fun fact: Diffraction in optical system is actually a "real-life" application of Heisenberg's uncertainty principle. The opening of a lens defines the position of a photon, which causes the an corresponding inaccuracy of the momentum of the photons and hence their direction, causing a blur.
Tony, you need to read more. Photons have no charge and no mass. They can however be influenced by gravity, which in short is a product of mass. Photons contrary to common sense operate like particles and like waves. Here's a suggestion. Short story: The macro scale analogy involves taking a bucket, fill it with water, toss a pebble into it and you'll waves. Now place a board with slits toss a pebble into said bucket and you'll see waves forming interference patterns, i.e. defraction, that is to say waves cancel and reinforce one another, as they pass through the slits. Abstract to small aperture photography light probably (after all it is quantum physics) forms similar interference patterns as it passes through a small aperture.
As we used to say if you want to prove that, you'll need a bigger grant; if you want me to prove it get out your checkbook. If I explain more I'll have to add footnotes and a bibliography. One last remark, notice I did not bring the issue of wavelength, which for photography can be summarized as the ROYGBIV phenomenon.
Excellent video. Thank You.
I was wondering why the pictures were coming out blurry in the background- when I decreased the aperture to f/20-22... Lens: Canon 85mm f/1.8. Mystery solved.
While the main point of Tony's video is valid. "Smaller apertures do increase the effects of diffraction" The explanation is kinda off. I think a some of the confusion is caused by confusing the physical phenomenons diffraction and interference. Diffraction is the bending of light at the edges of an obstacle (the aperture blades in this case) Interference is when light (or any other wave) can cancels itself out because of being out of phase with another other light. When people think of an diffraction pattern its actually an interference pattern that is caused by the diffraction of light allowing the light to interfere with itself at the plane of the sensor. Diffraction is is very well understood in wave mechanics via Huygens principle. The quantum mechanical description produces the same results so its generally not required to get into the quantum mechanical description.
Nerdhole alert, apologies in advance (I think that Tony & Chelsea's is the best photography channel on youtube - great scope, depth, balanced, generous, candid, honest)....
The basic point that diffraction effects can degrade images when the aperture is small enough is right. So why would I ramble on? Too much time on my hands, that's why! (And I should probably have read for others who beat me to this.)
I'm curious about who is saying that there is some confusion over diffraction. There is certainly interest in surface effects - what happens at the boundary between two materials, but that isn't the issue here. This is a problem of classical optics, much of which has been well understood for over 200 years. It cannot simply be electrons interfering with photons. Photons are massless and carry no charge, and the mass of the blades of the aperture is too small for mass-energy equivalence to play an observable role. But the real giveaway is that you can make a pinhole or slit out of any number of materials and see the same diffraction effects (assuming the pinhole or slit is of a constant size and quality and the materials are of equal thickness). In classical optics, diffraction is a product of the interference of waves. Classical optics is an approximation, but more than good enough at macroscopic scales. (Much the same phenomenon is at work with sound, which is why you can hear someone around a corner even when there is no surface for the sound to bounce off.) In quantum mechanics, particles also have wavelike properties, so you also see diffraction in quantum mechanics.
One more nerdhole needle: There is a lot to be said for photographers understanding a little physics. For example, people used to go on and on about the superiority of semi-matte or matte finish displays over glossy. (I don't see much of this anymore, but maybe I'm just not paying attention.) The matte finish on a display is, in effect, a diffusion filter. It kills reflections, but it also degrades image quality. A little physics might also put to rest the cult of curved displays for HDTVs. Great for an imax or huge 70mm screen at a theater. Largely pointless even with a large screen at home (except to the extent that it also mitigates reflections).
When I first started product photography I had only a little knowledge of photography. I had to use a high F-stop to get larger products in full focus. So I had a huge issue with diffraction and aberration which led to a lot of time in Photoshop. Once I learned about focus stacking my images improved considerably. Thanks to Tony and Chelsea, Jared Polin, and other gurus on youtube, I have learned so much. Thanks, Tony & Chelsea.
There are two theories of light and both are correct even though one does not explain the other. The quantum theory and the classical wave theory. The quantum theory applies to light when it strikes an object, e.g. when light strikes the sensor. Quantum theory of light does not explain diffraction and diffraction does not explain quantum theory. The wave theory explains diffraction and is used where light travels from its source to another object as a wave, these waves explain diffraction.
Diffraction is where the light waves of similar wavelength when passing through a small aperture will interact with each other, some waves will add to other waves and some waves will subtract at the aperture, what leaves the aperture will be something different. If you throw two or more stones into a pool at sufficient distance apart you will see the concentric circles interact with each other causing diffraction.
Photons are electrically neutral so how would a electron attract a photon?
Just because you can't understand the physics doesn't mean that everyone doesn't understand the science. QED is one of the most detailed and well tested sciences that there is. Your attempt to use a photon as a particle, but photons have a duality, they are also waves. Diffraction is more of a wave effect. You have also not fully grasped the statistical nature of quantum effects. All together you just can't simplify these complex effects with your simplistic everyday experiences. If you want to understand what is going on do the math!
You should watch the video first
The interaction that causes Airy circles is a complex dance between the electromagnetic waves (photons) and the electric fields of the atoms and molecules that make up the material at the edges of the aperture. This interaction at the boundary is what leads to the diffraction of light. So you are correct in that regard.
Great article. What you are missing is the diffraction is affected differently by the medium that the particle is traveling through. The denser the medium, the more extreme the effect. Water is denser than glass, which is denser than air. So the light waves travel through the air and are slowed down by the glass, which causes bend. This bend is also affected by the tighter aperture, which applies more resistance or impendence to the light waves, which causes an acceleration effect due to the increases pressure.
Thanks as always! Your physics explanation is not quite right… the wave functions of light and diffraction through empty space and matter are well understood, just pretty complex. Photons are not “attracted to electrons”. All that said, the practical recommendations about how this should affect a real world shooter are spot on!
Wave theory and diffraction are well understood with near and far field approximation as well as computer aided lens design. And diffraction does NOT wreck sharpness, it is an inherent property of light, and depends on the wavelength and aperture size. It is like saying darkness wrecks image quality.
When you are talking about diffraction interference with a smaller aperture you should be be expressing the destructive interference as a wave not as a particle. Some mention of telecentric lens properties to mitigate this would be illuminating and germane.
Conventional lenses have angular fields of view such that as the distance between the lens and object increases, the magnification decreases. This is how the human vision behaves, and contributes to our depth perception. This angular field of view results in parallax, also known as perspective error, which decreases accuracy, as the observed
measurement of the vision system will change if the object is moved (even when remaining within the depth of field) due to the magnification change. Telecentric Lenses eliminate the parallax error characteristic of standard lenses by having a constant, non-angular field of view; at any distance from the lens, a Telecentric Lens will always have the same field of view. See Figure 1 for the difference between a on-telecentric and a telecentric field of view. Basically Telecentric lenses use the sweet spot of the sensor. The larger aperture of the "Nikon S Line" Z-mount are more telecentric than their F-mount brethren. Olympus went 4/thirds for this very reason, to increase the telecentric properties of their glass.
As far as I understand physics, diffraction is perfectly explained by quantum mechanics. It's exactly the same type of "self interference" as in double slit experiment, but instead of two slits you have a superposition of "infinite number of slits" with decreasing magnitudes the further you get from the central path of the photon.
Came to say this, but also that since light is a wave, it bends around corners (double slit experiment) and thus more bending when the hole is small
Came to say this, but also that since light is a wave, it bends around corners (double slit experiment) and thus more bending when the hole is small
Came to say this, but also that since light is a wave, it bends around corners (double slit experiment) and thus more bending when the hole is small
Came to say this, but also that since light is a wave, it bends around corners (double slit experiment) and thus more bending when the hole is small
Came to say this, but also that since light is a wave, it bends around corners (double slit experiment) and thus more bending when the hole is small
Thanks, Tony. I was shooting a picture of a historical building in my town and I had this happen. The building had two towers like you would see in medieval times. I must have used F11 and the top of those towers curved inward. If that wasn't diffraction then it was caused for a different reason. I will try and go back to the site so I can shoot several at F8 and lower, then use F10 and up. Tried correcting this in my processing software to no avail. I will also try changing the focus point and see if it still happens.
Is is due to perspective as well as your lens distortion. Nothing to do with the aperture.
You can correct this in some advanced retouch software such as DxO.
tony, your physical explanation is scientifically wrong.
Please read up on diffraction again. There is NO ATTRACTION of the photons by the electrons at the edge of the iris. I don't know where you get that from.
... my background: optic/laser physicist ;-)
the phenomenological explanation of it is alright though... for photographers. My recommendation is: Please don't seed fake news, it's better to simplily instead of coming up with non-truths :)
randfee how about explaining than why and how it’s happening? Or post us, please, a link at least where to find scientific explanation
I agree, perhaps Tony should replace "attraction" by interaction. I wonder if the wave lights closer to the diaphragm experience a combination of mirage plus pinhole effects. I mean, some partial refraction trough the surface of the diaphragm with a low-pass filter.
are you telling me the Coanda effect doesn't apply to photons!?
Daniel Clarke: I think the Coanda effect is more like water tension, like the way water rolls around a soft radial edge ( like a rain gutter hood) until it’s mass causes it to fall. But then what do I know.🥴
Douglas Michel yeah, that’s the joke
Very nice info. Lots of people forget, or just don't know what is actually going on inside the camera to come up and resolve into the image you get.
A proposed subject for a tech-oriented explanatory video: Consider the actual measurement of the diameter of the aperture of fixed aperture zoom lenses in contrast to the actual diameters of the apertures of variable aperture zoom lenses.
The definition of f-stop as f (which equals focal length of the lens) divided by the diameter of its opening (aperture) suggests that when a fixed aperture zoom lens is zoomed the actual measured diameter of the lens' aperture must be increased if the fixed value f-stop is to be maintained. Some definitions include mention of optics inside the lens modifying the effect of the actual measurable physical diameter of the aperture to produce a nominal equivalent diameter .
It would be interesting to see just how much the measured diameter of the aperture of something like a 70-200mm f/2.8 lens changes when the focal length changes throughout its range, and to contrast that range of actual diameters with the changes in aperture diameter of a variable aperture zoom lens such as a 55-250mm f/4-5.6. If I understand correctly, the measurement of effective aperture changes of the fixed aperture zoom lens might actually be greater than those of the variable aperture zoom lens.
Most people believe that their lenses are sharpest around f8-f11 but most lenses are sharpest around f4-5.6. I think people believe this because shots taken at f8 are more likely to be relatively in-focus edge-to-edge and it's easy to confuse something that is slightly out of focus with something that isn't sharp.
That's silly, Tony. A photon has no electrical charge. Electrons should have no "pull" on a photon. Just imagine if we could bend light with magnets or static electricity!
I think, lack a clear physical explanation, Tony was employing a metaphor. He's a knowledgeable guy and understands the basics of electrodynamics.
@@meta4101 You must be very intimate with Tony.
@@eurobum2012 Just an intelligent listener like your ...
@@meta4101 it's the basis of quantum mechanics that is needed here, which means dealing with wave equations when talking of photons and electrons. That's a whole lot different to electrodynamics, which is classical pre-quantisation model and really isn't appropriate at the quantum level.
For that, you need quantum electrodynamics (QED) and it's clear that Tony is not familiar with that. It's not surprising, as that requires degree-level physics.
@@TheEulerID In a sense, all physics is qm. That said, diffraction is more easily explained classically than the 2-slit (self) interference of qm and was well understood in the 19th century as a wave property of light well before qm was devised in the 1920s.
Like some already mentioned, the science in this video is lacking a bit. The light behaves as a wave and a particle in the same time. In diffraction is the wave side of light that comes to play. The waves of light coming till the aperture are close to parallel, and once forced thru an aperture they take the curved shape due to the waves of light interfering with each other (not with the walls of the aperture). It's like looking at the waves formed in a lake by throwing a stone. Near the impact point, the waves look so round, but at a distance looking in the space of a few cm/in across, the waves look flat, parallel.
Tony , whilst I agree that diffraction ruins sharpness, your explanation may be misleading. There is no value in considering how photons are 'attracted' to the edge of the aperture, since diffraction will occur regardless of the properties of the material used. You could electrically charge the aperture to no avail. Diffraction is absolutely only dependent on the geometry of the aperture and is the result of the destructive and constructive interference of the light wave as it passes and bends through the circular diffraction slit, which in this case is the aperture. Diffraction can only be understood by considering the wave model of light, not the photon model, and that wave-particle duality of light is the conundrum of quantum mechanics. The diffraction pattern of the circular aperture is called the Airy disk, mathematically proven way back in 1835. Consider a point source of light in the object plane that has a single wavelength, this presents a wavefront to the aperture that results in a corresponding point on the image plane, but that imaged point will exhibit an Airy disk, albeit very small but bigger than the original point light source. The width of this Airy disk X is a function of the wavelength L, aperture f-number N, where X = 1.22 LN.
NOW, consider that any scene we want to photograph is made up of essentially an array of point light sources, all of which produce an image at the image plane. We can consider these light sources as object pixels, so that each 'pixel' in the object plane corresponds to a pixel on the sensor image plane. The light's wavefront from each object pixel hits the whole aperture and results in an Airy disk at each sensor pixel in the image plane. At a certain aperture f-number and wavelength, the width X of the Airy disk can become bigger that the sensor pixel pitch, and hence you start getting smearing across pixels and a less sharp image. For example, at N=f/11 and L=420nm, X=4.6um, which can be bigger than the pixel pitch of many sensors. Given that the light from most scenes is a mix of colors and hence wavelengths, these wavelengths produce Airy disks of different diameters (similar to chromatic aberration), which produces additional smearing.
Conventional optical approaches cannot get around diffraction, but I live in hope that the nonlinear approaches used in high-precision photolithography, used in making integrated circuits, will be adaptable to camera optics to minimise diffraction effects.
Enjoyed the video. The nitty gritty of knowing why diffraction happens is less important than knowing that it does, lets go take some pictures! Just finished a backyard bench test of my new Samyang AF 85mm f1.4 and I can clearly see flare and diffraction in action :o)
@Otto Danby II So....what's the sweet spot and how does it compare to wide open?
High frequencies difract less than low frequencies thats why sound diffracts around objects because it has a very long wave length from cm to many metres, whereas light wavelength is in nano metres so it does not diffract around objects it is blocked by objects.
Interesting and well-explained, thanks! I knew this phenomenon occurred from results from my photography, but I didn't know exactly why...I just kept away from higher f stops because photographers who mentored me over the years said the sharpest results are found around the "middle" of a given lens (maybe 5.6 or so)
I can't say what the physics are, but I thank you for bringing up this topic and giving us a nice simple mental picture that is sufficient to convey the effect and what photographers should do about it.
I join you in asking those who know a more correct physics explanation to explain it as simply as you did. Just saying "Airy disk" fails the Fenyman test in that it provides knowledge of words without providing actual knowledge of the subject. So we don't need 500 people commenting with that, we just need the one who can explain the thing to a 6 year old (or an undergraduate). Until then I'll use your mental picture.
Thanks for the video and please more such on technical subjects and practical photography techniques.
Also, thanks to you and Skillshare for the 2 months free.
Folks below are waaaaay too caught up on the specifics required to understand this. I think your explanation for understanding the reasoning behind this is fine. An interesting way to prove the concept of waves bending would be to either watch a video on why the centre of a circular shadow is the brightest point (it's well trodden territory) or if you're at a large body of water just watch how waves interact with a solid pier or jetty.
Glad I watched this either way as I hadn't put much thought into why diffraction occurs, this has helped a lot with picturing it in my mind and cemented it.
Thanks Tony :)
Tony, I love this video. A great science communicator Brian Cox did his PHD in difractive scattering. While I am not a physicist I have always had a great yearning to know more about high level physics and came across his work a few years ago. It goes into a bit of depth about what you are talking a with photons interacting with electrons.
Well, it might mean that sensor size is not that important for landscape, since we would be limiting the amount of light on bigger sensors to a greater degree anyway, applying crop factor to aperture.
Diffraction is totally well-understood by physicist. It and the interference phenomena are taught in 1st year Physics at University or even earlier in some cases. You may check any 1st year Physics books for a good enough explanation. And forget your photon story. :) a discussion of the actual aperture size with respect to visible light wavelength would have made more sense.
Watch out ... all of the Sheldon Coopers are going to have a field day on this. ;)
Quantum physics has a principle called the Heisenberg uncertainty principle, which states that for any subatomic particle the more precisely you measure the change in position (I.E. the path a photon takes from the subject to the sensor) the less precise you can determine it’s momentum (I.e. to what degree the aperture blade will deflect the photon from a direct path straight to the sensor)
The light doesn't cross at the middle of the blades but at the middle of the lens. Some photons actually hit the side of the blades at angles and bounce of it. At the size of a photon the slice (side) of a blade is not thin at all. When the blades are wide open (f1.4) the angles of bouncing photons are more different and doesn't really affect the image at a fast shutter speed. they are more distributed on the sensor. But at f22 the angle of bounce is thinner and at a lowest speed it affect the image.
Seems to me it matters a LOT that you don't mention the role of the lens. Light reflected from a point in the scene diverges in all directions. A number of different pathways are available from that point to its image on the sensor. That's the job of the lens: to redirect the diverging photons into a convergent bundle that all hit the sensor at the same point. (You focus the lens to make sure the point of the convergent cone is right at the sensor, not further or closer.) Therefore not all photons travel the same distance, and not all of them pass equally close to the edge of the aperture/iris. If there is any kind of diversion of path of photons due to interaction with the iris of the lens, that will not be shared by photons which travel through a different part of the lens. Every part of the lens is simultaneously transmitting photons travelling in different directions, on their way from scene to sensor. All these different divergent cones of light are being turned into convergent cones of light by the lens. That is why larger aperture lenses are harder to make sharp: the cones are fatter and it's harder to make the edges of the lens and the centre of the lens focus on the same spot. As the aperture narrows, a higher proportion of the photons in a given cone will be passing close to edges of the iris, and the disturbance to their paths ("diffraction", if I'm right) will have more effect in introducing blur. Takehome: it's the difference between rays of light (photon paths) which are meant to get from a single point in scene to a single point on the retina, via different parts of the open lens surface, which is crucial. I don't think it's anything at all to do with different photons on the same path being out of phase with each other. If phase differences matter it will be because of the spread of paths and the disturbance of some, not others, by the edges of the iris. Den Rob
agreed!
Photon path difference is only an issue if you have in-phase light to begin with. We photographers do not. The light path difference is entirely immaterial.
Top Rock Photography Fair enough except that one way of understanding light is that every photon travels by every available path and the result is a superimposition of effects. Feynman's way (in one of his popular works at least) of explaining diffraction effects involves discussing which pairs of paths are in phase, which out of phase, with each other, on arrival (of the same photon by many paths). Where there is destructive interference you get less light, where positive you get more light, the result is the various diffraction patterns you see. Diffraction of light either needs to be explained using the pretence that it's all waves, or else by reference to photons. Explaining why these particles produce wave-like effects requires quantum theory, which as another commentator has said, is err, not easy, mathematics.
@@denisrobinson8504 Fine for a double slit experiment, where we first send the light through a single slit to approximate one wave, then through a double slit. The double slit experiment does not work when there are two or more independent waves moving towards two disparate slits, into a common area. One photon coming close to the top edge of the aperture blade, can be treated as several photons moving in-phase in several directions from there, but a different photon coming close to the bottom of the aperture blade, will not cause a diffraction pattern which will interfere with the photon on the top in a predictable manner.
If the photon at the top was the same photon at the bottom, then that would be an entirely different thing.
[EDIT] To clarify, it works for a point source of light. When speaking of an image made from reflected light, (with or without sub-surface scattering, etc.), then we no longer get a homogeneous point source of light. Particularly true when their is another point source of light right beside it. It is the distance between two point sources of light increasing, and diffracting through an iris, which gives us the cone of confusion, or rather, the angle of the arc of the cone of confusion, which tells us how to get things sharp.
By looking at that, we see that the entire interference thing breaks down when we are speaking of multiple light sources, and even more when they are not homogeneous, as when we have SSS and even multiple sources of light reflecting off of a single point. (Bear in mind, that I am speaking of the interference thing breaking down, not the diffraction thing. Diffraction is still real, and still causes non-sharp images, and loss of detail).
To put it another way, when the difference in light path is on magnitude of λ, whee λ is the wavelength of the light, we can see a distinct interference pattern from the diffraction. As the path difference becomes of much higher magnitude, the interference pattern becomes less distinct, turning into an indistinct, graduated, blur, (even with a point light source of homogeneous light, and perfectly aligned circular aperture). So diffraction plays a greater role, interference plays no significant role at all. [/EDIT]
I usually don't shoot wide open, and if I accept that it might not be the most perfect. Whatever is needed for the situation right? Nor do I shoot at F22, unless yes there is Macro.
Is there a loss of sharpness at F22? Yeah even with a nice big sensor and nice big "pixels", there are still limits to how things work.
But a slightly blurry but artistically good looking shot, or a super sharp shot but only a little slice? That is the question.
Skillshare online learning is great, but problem with online catalogues and memberships is that they can be taken away at any time. Let's say I comment on a video and YT doesnt like my comment. They have the ability to wipe my history out, blacklist me, ghost my account etc. Same with Amazon, FB and the lot. I like physical books because you don't have 'big brother' watching your every move.
Tony, the variation in the distance from the edge of the aperture is a function of the role of the lens elements. Different paths of light from the subject are focused back on the sensor by the lens elements. There are different route to get to the sensor through the lens and these paths are all different distances from the edge of the aperture blades. This will have a far larger effect than the differences in the wave. That might only be an issue with a pinhole camera. If you included the elements in your diagrams and showed the paths from one point on the subject to one on the sensor, you would illustrate the issue better.
When you use small aperture, some light may be reflected by the aperture blade itself and make some disturbance in the are between lens and aperture blade. Different color of light have diffrent wave length and they bended differently when passing throgh the glass.
Tony great video. When light from a subject arrives at the sensor after passing through a thin slit (the closed down aperture) it does so half a wavelength out of phase with the light leaving the middle of the slit. These two rays interfere destructively. In other words, the light from one half of the opening cancels out the light from the other half. The rays are half a wavelength out of phase because of the extra path length traveled by one ray... I think.
Prediction: Ken Wheeler is going to pretend that he cant talk because hes laughing too hard. He is then going to say that you dont know any of what youre talking about and then something about magnetism....
tony's explanation is wrong, do you really take hid words as total truth instead of doing some research yourself?
Slight Nature did I say I agreed with Tony? I said how Ken Wheeler would react to the video. Take a deep breath, it’s just the internet...
@@schweglerd :P
DanSchwegler I can’t take Ken Wheeler serious because I’ve never seen his work: he talks the talk, but I can’t seem to find any portfolios of work other than some basic snapshots he puts on Instagram here and there.
If you've addressed this previously, I'd love a link, but this video made me think of something I deal with at times - chromatic aberrations. I shoot A LOT in the winter (in Alaska ~8 mos a year) and have found ways to deal with most issues. But I do like to use a prime lens at times (i.e. 35mm or 50mm @f1.8 or f1.4) when it is dark to get the most light possible when shooting things such as sled dog teams. Flash is prohibited in most of these situations. Anything you can contribute to getting the best images, of moving subjects, in near total darkness, without (or minimizing) chromatic aberrations, would be fantastic.
Very well made video. Thank you Tony. A humble request:
Please make a video on WHAT IS FOCUSING? What it means for an object to be in focus? How lenses change focus? And what exactly changes in lenses in order to change focus from one point to the other?
I have searched for this a lot but still don't have a good answer. I would be grateful if you could explain it.
PS Viewers also please reply if you have an explanation.
@@verybigheart What do you mean? I didn't get it.
Tony and Chelsea, I love your videos talking about various cameras. But, I feel that the best investment that a new photographer can make is purchasing your books. Beginners are not going to be happy with their photos until they learn the basics in my opinion. You two tell it like it is, and give invaluable advice. Thank you for all that you do!
As much as I like your videos on photography, the physics teacher inside me has to say this:
we know perfectly why diffraction happens. By the way, there is no "attraction" between the photos and the electrons in the diaphragm.
Probably not electrons. If you look at the edge of a desk or counter with good contrast behind it you can see light being lensed around the edge. Most shutters are a denser material than air and as such they attract the closest atoms of air closer to the surface of the edge such as surface tension in water. The denser something is the more it bends light and as the air molecules are denser near the edge, hence more lensing.
In graduate level physics "optics" we learn that photons are electromagnetic waves. Though more advanced classes look at the true aspect of the photon since that graph that we study actually spins 360 deg for each wavelength. (This is not bragged about since the spin would ruin the explanation for polarization) So, if it was electrons then you would have scattering in more of a Fraunhofer diffraction pattern.
I forgot to note that the lensing only goes out 10 to 15 atoms, it is hardly noticeable unless you are a camera nerd with 36 MP or better. PS I once took wedding photos of the rings and got too sharp. Every hair, every skin flake, and every grain of dirt, and there wasn't a softening software that could pull it out. 55mm 3.5 micro Nikon it matches sharpest Nikon lens made, Oops.
this should be easy to verify: get a monochromatic and coherent light source and check the diffraction
Some of the loss of sharpness at a wide open aperture is due to the difference in the distance traveled by two light particles from the same source: one thru the center of the lens, the other at the edge. The light at the edge travels a slightly longer distance than the light passing thru the center. When this difference approaches the wavelength of light, you get wave interference...
False. Only true with in-phase light. Light in the real world is not in-phase, thus the path difference is of no consequence.
I think just the reflection from the edges. Also a small aperture amplifies the errors in the glass surface that would be otherwise canceled out with open aperture. Also there are lenses that have very minimal diffraction even on F22
This effect has been proven by one of my students in the lab who purposely wanted to exploit this effect bending light to measure its component parts via a slit made from two close razor blades. It did act like a prism and also bending the white component part light. Unfortunately the previous effect wasn't investigated further.
Diffraction was always a function of Focal Length. I shot on 11-14 and 8-10 cameras. We had to use F 90 and F 132 with big bulbs. I always used at least 2 stops down. I found that I could not use f 16 on Macro 4/3 Macro Best results where at 1 stop down from wide open. Full frame Nikon lenses would handle 16 but not 22 without serious degradation. Hasselblad lenses always seemed best wide open. But times change.
Is the thickness of the apperture blade a factor with diffraction? Could thinner physical apperture blades reduce it?
I often enjoy the videos on this channel. I must echo other comments about the incorrect scientific explanation here. I suggest looking up the wave particle duality and the DeBroglie wavelength. As you mentioned the double slit experiments, that is important here. Depending upon the wavelength, there is a size of an opening at which diffraction occurs. Light passing through a smaller aperture perpendicular to the opening will not suffer from diffraction. As the angle of light approaches the plane of the aperture, it effectively makes the opening act as though it’s smaller - small enough to cause diffraction.
Short version: smaller openings means light off axis from the normal to the plane of the opening have less wiggle room to be off axis.
My Fuji 10-24 at f/22 is so horrible, diffraction is so bad it looks like its out of focus. Open it up to f/8-f/11 and it is just mind blowingly sharp. I hope Bryan Peterson's 4th edition of Understanding Exposure corrects his statement on diffraction because in his 3rd edition that I have he said it doesn't matter, maybe in the early 2000s and the 12mp sensor he was using. But now with crazy high megapixel sensors and high resolution displays...it very much does matter now.
Saying 'regardless of the camera' is incorrect since a larger sensor with a larger pixel pitch will not be affected as much by diffraction patterns.
Let's just say the light near the iris edge "trips" over it. Not scientific but sufficient for a photographer's needs. I generally try to stop down at least 2 stops from wide open but not beyond about f11. Generally I prefer a bit of blur with things in the foreground with landscapes. Macro often requires f22 or f32 to get adequate depth of field.
In 1982 I bought a Tokina 35-105 lens. It was advertised as the first computer designed lens. The color images were always muddy. With a magnifying glass I could see color separation. It was like I'd stacked 3 images, each with a very slight offset. It happened at all f-stops. It was either a bad design or poor coatings. I gave the lens away and used nothing but fixed lenses for decades.
i'm still using the tokina 35-105 f3.5 to this day.
I believe Nikon was using a computer to help design lenses somewhere around 1970. Something I remember reading when reading the history of Nippon or Nikkor lenses. JFYI
I'll bet there were many stacks of computer punch cards involved. ;^)
I think Tokina was being a bit loose with their advertising there. The 1974 Vivitar Series 1 70-210mm f/3.5 Macro Focusing Zoom had its optical elements computer designed by Opcon Associates, and from research it appears that electronic computers were being used back in the 1960s. That's not surprising as prior to that it took a lot of human computers to do the calculations.
Are light waves affected as they pass through glass? Camera lenses are comprised of many lenses. Perhaps light waves traversing many glass elements are tweaked off their original paths thus softening the image? With this in mind, I usually set my stops around F8 as a safe average. This seems to be an average sweet spot for most lenses. Cheers.
Doh, that's what the glass is for!!! The light MUST be bent off its original path. All over the lens surface, light waves are being bent in the hope of bringing the right clusters of them together at the right points on the sensor.
Thank you for a good explanation. I remember with our small-sensor video cameras around 2010, using the built-in ND filters are so necessary. Without it, not just soft - so soft the footage was useless.
Always thought that diffraction, through any medium at any scale was a result of Huygen's principle. Looking forward to a follow up. Thanks for all the great videos!
Huygen’s principle is one of correct ways to look at it. Tony’s explanation in this video is extremely wrong.
It makes sense that the light rays from differing angles from same field of view, having to pass through a smaller aperture, will interact with each other more in a asynchronous manner.
I love geeking out on the techie side of photography. Please make as many videos like this as you can. Good stuff.
How does a camera know that what it's looking at is 3 dimensional, and that tree X on the other side of the lake is 150 feet away, while tree Y is 220 feet away? I don't understand why depth of field exists at all, and no I have not even bothered to research it. From the camera's point of view, it should see a flat environment and everything is equally in or out of focus.
Well, your thought on how the photons interact with the aperture wall are not quite right. It's not like they're out of sync and some get "closer" because their wave peaks are closer to the wall than others. What happens is that photons do act like waves, waves that interact with the particles in the aperture. This is a quantum-mechanical effect, but it can be thought of just fine at these scales are macro-scale waves (like water waves). Some of those photons pass closer, and they get diffracted more, some are further and get diffracted less. So you get a spread because of that. Overall I'd say that this is very well understood by modern physics.
F8 and be there ! (or 11... on a 22/32) - and focus stack when you must...
'When you believe in things you don't understand, you're sufferin' from superstition.' S. Wonder
I don't know, but wonder, how much optical companies have experimented with the edge of aperture blades to affect diffraction. If we consider diffraction in photography to occur as it passes the edge of the aperture, what occurs to diffracted light as it is refracted by at least 2 to perhaps 8 glass elements after?
Probably the aperture is close enough in thinness to come close to the wavelength of the light, thus bending it around (similar to why we hear sound around corners, but don't see). The same effect is responsible for why leaded glass is translucent but still holds off a massive amount of x/gamma radiation. An interesting experiment would be to see whether the amount of diffraction differs between shots dominated by different colors of light. Some should be deflected easier than others.
Longer wavelength do diffract more.
Thanks so much, Tony. Love your work. Question: So defraction at f11 on micro four thirds is the same as f22 on full frame?
The size of the diffraction spot on a focal plan dépend more or less of the f-number, the larger the f-number the larger is the diffraction pattern (google airy disk). A f/22 lens will have a diffraction spot twice larger than a f/11. However it’s proportion to the picture (the sensor) will be the same when comparing a f/22 on a ff and a f/11 on a M43.
Sylvain Guieu Thanks so much Sylvain. Got it
This was a great vid Tony....Thanks for that..... Way more useful and more educational than most photo vids out there....
Great video Tony! For landscape, I prefer micro 4/3ds, for some reason I can see more sharpness with less aperture.
Hi what camera and lens are you using for your tests? I haven't tested what Tony is talking about and I'm somewhat new to still photography and I recently bought a Panasonic GH5 and using Panasonic vario 12mm to 60mm lens and a Panasonic vario 45mm to 175mm lens.
RockstarBruski Hi, Most of the time I use panasonic G9 with kit lens panasonic Leica 12 60, I heard great stuff about GH5 in photography too, however, as Tony said, there is a lot of factors that affect sharpness but getting a decent lens like the panasonic leica is a good start.
@@GermanViking ok thank you for the information :)
OK Tony, how do you focus stack when your lens suffers from focus breathing as most seem to do to at least some extent.
Crop.
Does the software adjust for focus breathing while focus stacking?
Ask Destin at SmarterEveryDay. That is his UA-cam channel. He will figure it out. His channel is awesome.
I would put it out to Dianna Cowern aka PhysicsGirl. She's clearly loves optics and lasers, and since she has a physics background I think she could approach this subject more intuitively.
In colab with Veritasium
It's simply planar waves and obstacles (in this case, the lens frame or the aperture). The larger the diameter of the front lens, the better the (theoretical) resolution. Just see astronomy, there you have nice explanations about airy discs, size of main disc and light distribution in harmonic (diffracted) discs.
Finite optics will never generate a point picture from a point source. You will always end up with a Fresnel distribution of light. The more you stop down (higher f-stop), the more you will see diffraction. There is no secret about this issue. Ok, one might argue about the contrast (or ligt intensity) of the main disc in comparison to the spurious ones….
By the way… light is known to be a longitudinal wave… what you draw is transversal… big difference :-)
Let's call it the Northrup theory of diffraction since it is different than existing scientific theories of diffraction. The hardest part to defend will be the aperture edge electrons pulling the incoming photons onto a different path. Electrons have a negative charge but photons have no electric charge.
Dude! Totally get you are shooting in your kitchen, can you please lav mic or have a close shotgun in the future for these. The sound is absolutely killing me!