Well said. Even my high school physics text book tell me one single convex lens can make a perfect image everywhere, like if your object is 2f from lens then you will get a perfect image on 2f.
Yes, Lenses can be very complicated to design, on one of my many visits to the old Hasselblad Factory, I was told that the Zeiss Biogon 38mm 4.5 took a long time to design and calculate, the amount of A4 papers used for calculation was a stack of one meter high ! I had the Zeiss Mutar 2x teleconverter, after I told the folks at Hasselblad how good it was on the Zeiss Planar 110mm 2.0, they got very interested and wanted to learn more, later I was told that Hasselblad had bought a computer from Canada to calculate Lenses. Today all Lens makers use computer software to calculate Lenses, and Lenses today outperform all older Lenses.
What year was that? Sounds like it was before the microcomputer era. "Today all Lens makers use computer software to calculate Lenses, and Lenses " and today all businesses use word processor software...
@@JohnDlugosz I do not remember the exact year, late 1980´s or early 1990´s, but Hasselblad designed fx the teleconverters 1.4x and 2x with that software. Hasselblad followed my experience with the Zeiss Mutar 2x which I used on different Lenses, it worked really well on fx Zeiss Planar 110mm 2.0 T* F and Zeiss Tele-Tessar 350mm 4.0 T* F, so Hasselblad tested how good the software was by designing the teleconverters, the 2x Hasselblad converter was just as good as the Zeiss converter !
Clicked on the video thinking that this is the start to my journey of making the most compact 1.4 primes to be ever made. I’m just gonna stop while I’m behind.
Thank you for this. Just a historical note regarding the Cooke Triplet: it was designed and patented in 1893 (not the 1930's) by Dennis Taylor who was employed as chief engineer by T. Cooke & Sons of York, England. Its earlier provenance makes it the more remarkable.
Cooke Triplet is also basis for all zoom lenses: Moving center element in between outer elements changes its focal length. But also aberrations change and are harder to control and it took until 1930s to get first zoom lens into production.
There seems to be no limit to the number of technology fields that you are great at explaining/teaching. I would have loved to have you as a teacher/professor IMSAIGuy. Thank you for making these videos for us fine sir! Fred
Another trick they've been doing recently for mirrorless cameras is that since you've got to apply digital processing to the sensor image's anyway, some corrections can be done in software and the lens design can be optimized for other factors. If you squint this is a analogous to the curved film trick you mention in the video.
Ever since I learned about the principles of lenses and telescopes in middle school, I've always had this question: Why do these telescopes and camera lenses contain such complex lens assemblies? Now, at the age of 34, I finally found a satisfying answer in a random UA-cam video I clicked on. Thank you
Really interesting. I've been a photographer for decades, and I'm a little ashamed to say that however mind-boggling I always found lens techniques to be, I know way too little about the 'glass' that I use. Thanks and thumbs up.
I have an Astro-Physics apochromatic triplet, with the 3 lens elements in contact with each other and oil spaced to reduce internal reflections, and improve transmission. I love this thing! For as much as it costs, the field flattener accessory comes with quite a breathtaking price tag; but it was intended for medium format film photography at the focal plane. Fortunately, at the time I acquired it, only APS-C sized CCD devices were practical (affordable!) and the part of the focal plane I was using was "flat enough". Later I move to using a Riccardi-Honders astrograph, an f/3.8 optical system and quite a novel design. You might mistake it for a Schmidt-Cassagrain but it's actually more like a folded refractor with a rear silvered lens, and more importantly, I believe all spherical lens figures. And a nice, large and wide flat focal plane! Only suitable for astrophotography, but that's the problem I had. Never had an eyepiece in it. I asked the designer of that telescope why he didn't use carbon fiber or some other material with low coefficient of expansion due to temperature for the tube assembly, rather than aluminum? That was a deliberate choice, the dimensional change of the tube due to temperature offset the changes in the optical elements as they also cooled down. There is quite a bit of "art" to go along with the science. Difference between theory and practice and all that stuff you learn the hard way. Optics are cool! Really nice optics are very cool and expensive! And definitely one of those fields where there's no single "best" tool/design. It's always a tradeoff over a bunch of factors, including $$$ it seems.
Very cool. I've wondered about this, off and on, for decades and never got around to looking it up! One thing I *think* might be missing is that you can use materials with different indexes of refraction for each lens to tweak it even more.
yes, glass with different dispersion, to correct for color aberrations. classically referred to as crowns and flints. I talk about it a little: ua-cam.com/video/PxqhA37bKtI/v-deo.html
Likewise. Interesting to note that the more glass elements you have in a lens, the worse the image quality. It goes something like this: more glass = less light (in terms of F stops.
@@chawenhalo0089 That was true before the development of lens coatings which have been improved to a point that I think 99% of light is no longer lost now due the reflection at each element. This is why before lens coatings many classic designs were limited to not many elements 3 to 5.
@@dwaynepiper3261 😅 I ain't that old! Was thinking about the difference between Nikkor "D" series lenses compared to AFS. I get far cleaner images (depth of field, chromatic aberrations) on my old 80-200mm than on the far easier to use AFS 70-200mm (the latter being noticeably sharper when croping); both 2.8. Horses for courses as they say... That's purely down to element count... and me romanticising of course.
Could you comment on how different colours/bandwidths are reconstituted/merged? In most of your diagrams it appeared to show different colours focusing at different points. Thanks!
What you mean 'bent the film into a cylindrical section' ? That only helps with the one axis. Wouldn't it need to stretch the film into a spherical section to provide axially-symmetric non-planar focal surface?
Enjoy this video because I’ve always been fascinated by optics. And it is definitely a mathematical situation. Zeiss took the triplet and turned it into the Tessar , which has certainly stood the test of time as well. Thank you for sharing your thoughts here because it is truly a fascinating video. I look forward to seeing more of these and sharing your knowledge with us layman. In order to get a flat image the curvature of one lens has to be similar to the other to cancel out the curvature of the other lens. That’s why lenses became symmetrical to cancel the curvature of the other lenses. The hologon lens by Zeiss is a good example of this like two opposing marbles cut in half. The Japanese did the same as you, cut the old lenses in half and reverse engineered them and actually eventually made improvements on the Planar and Zenitar designs which many of their lenses (Nikon) are designed after.Regards Gerry
"The Cooke triplet is a photographic lens designed and patented in 1893 by Dennis Taylor who was employed as chief engineer by T. Cooke & Sons of York".
2:20 Is that why on telescope (doublets, almost like one convex lens) need a field flattener to focus the corners of the image, or is that another thing?
This is really interesting.. Wide angle lenses are hard to design for, makes sense getting the focal plane flat is the hard part, that's my walk away. I wonder about 600mm lenses at f4 costing $15,000 for like a Sony camera system, is that the cost of materials?
They look similar but are quite different. The Schmidt plate is at the aperture stop of the system. There is a Fourier transform from the aperture to the image. the image is in x-y space and the aperture is in angle space. The incoming wavefront will be phase corrected by the plate to correct for spherical abberation and I think astigmatism and coma. it is difficult to grind an aspheric mirror so the job is given to a thin piece of glass that can be warped, ground flat, and unwarped to result in the shape.
this explains pretty well tho why it took a (comparatively) long time for compact cameras to gain lenses that went wider than 35mm (equiv.) guess it's just that - harder and more expensive to make light bend around alot more at wider angles
Great work Sir ! there is so much to learn. Gone through your channel, quite inspirational, started really loving what you're doing. Thank you so much.
I could teach you how to do lens design and loose all my viewers. They only care about RF. In silicon valley I can count the lens designers on one hand. My buddy in San Diego designed one of the mars rover lenses. He is quite proud.
@@IMSAIGuy Similar configuration is used in a electron microscope. It has almost an ordinary sensor but with bonded fiber glass and ndyag scintillator plate. Maybe you could do some research how it is bonded ? This way a microscope could be done in a very cheap manner.
I have numerous text volumes on optical design all very interesting to read and yes specialist lenses are incredibly complex. Thank you for a fascinating rundown on camera lenses. I particularly enjoyed the end bit about lens design for phone cameras. Once again, many thanks for the great info.
At 06:50 Yes, the use a lot of elements for a single lens. More so if you consider that they use a very narrow band UV light source. Chromatic aberration is therefore limited, EDIT: Good to see that you mention it also.
I randomly came across this video in my feet and it’s super interesting. Do you have any explanations as to why wide angle lenses get longer as you zoom wider? It feels like if I am increasing my field view lens should be getting shorter but the front element always goes farther from the sensor and I don’t understand why.
This is so cool! Thanks for sharing. I believe the optical coating is also important, isn’t it to ensure the light entering the lens is within its comfortable zone (generally using thin film reflection to bounce back the other ones)
Thanks for the clear explanation of why we need so many layers of lens in cameras. I have a stupid question, I am wondering why our eyes can do it so good with only one lens? Is the lens in our eyes any special?
well explained! could SLR or DSLR lens designers use the cell phone field flattener lens type to make a minimalist sise lens for full frame cameras? too hard to grind complex shape in bigger lenses?
I would be interested in more videos like thsi, i have been trying to research building a triplet telescope for a while but i havnt found any triplet sets so the idea is to find out how to select individual elements, problem is nobody actually explains it well at all. Are there any open source tools for this? Or any actually useful resources?
I would get the book Modern Optical Engineering by Warren Smith if you are interested in lens design. CAD tools I've used: ZEMAX, OSLO, Code V, LightTools. once in a while MATLAB or Octave for specialized calculations and color theory. OLSO may have a trial version, you can also try WinLens3D
7:16 This style of cheating was also good for black and white photography, in that since your photosensitive medium will only provide you with shades of grey, you don't need to expose it to all the colours of the spectrum. So with black and white photography you could address the problem of a lens with poor chromatic aberration, by using a red, green or blue filter when taking the photo. Whack a red filter onto the front of your lens and now the blue and green light that is causing blurriness on contrasty edges, is gone. Get yourself some really nice darkness for blue skies too, to make those white clouds pop! Edit, never mind, you mentioned this! LOL
The current 80s night vision design is I think a 7 piece direct to the PC. The PC to anode phosphor screen assembly is proximity focused onto that FOB which may be inverting. The objective is blue blocked to deal with CA.
Where do I start if I want to measure a lens and figure out its parameters? I have a huge aerial photography lens, the first element is nearly 6 inches in diameter, and aside from focal length and aperture, I'm a bit in the dark. The front and rear halves unscrew from the shutter (no adjustable aperture, just open-close). Taking a giant lens spanner to the front, it's just two elements. The rear has 3 elemens, one single and two glued together. Since it's fixed focus as well, I'm pondering how to make it adjustable focus - the easy answer might be to mount the lens on a rack / bellows type movement, but I've been testing it out on the kitchen counter using a sheet of paper to gauge the focus and a ruler to see how much movement is required, and for the range of distances I'd like to use it at, I need over a meter of travel. The bellows would be bigger than the camera and require some support to keep out of the optical path. Just for fun, I calculated the hyperfocal distance and its around a mile.
that is a very complicated process. you need to measure the curvatures of each surface and the thicknesses and spaces, then you will need to know what glass type is used for each element (index and dispersion). these will all require special instruments. once you have these number they will not be accurate enough. you will need to put them in an optics design program to adjust them.
I would get the book Modern Optical Engineering by Warren Smith if you are interested in lens design. CAD tools I've used: ZEMAX, OSLO, Code V, LightTools. once in a while MATLAB or Octave for specialized calculations and color theory. OLSO may have a trial version, you can also try WinLens3D
That's really interesting how you explain how lenses is working, so most people can understand, or at least have an idea about it. I subscribe to your channel because you have a lot of good interesting content. Greetings from Kenneth (Denmark)
I have a Cooke Triplet design lens. An old Meyer Optik Domiplan. Modern lenses actually use too many elements IMO. Most modern photographers only care about sterile perfection in lenses. The older Leica Summicrons only used six elements with a Double Gauss design. Not sure about the newer ones.
Great video. At 2:22 coma is Latin for comet iirc. Goes all the way back to Galileo era star gazing. 3:14 I believe Cooke 'tool inspiration' for that design from the Chermans. 4:04 T1&2 are important, historically, T3 onwards are junk and to be forgotten. That's when James Cameron was no longer involved. 4:16 Radiuses? Radiiii? 4:40 Triplet, tri, tre, more latin. 10:57 There are curved sensors, I'm not aware of any that have been used in mass produced devices though. If curved sensors do exist in cameras, we can purchase, probably mated to fixed lens (non interchangeable) and probably of a fixed focal length. Fun Fact; nothing can correct for the obvious aberrations in my personality.
Very interesting! I'd also like to learn about aperture, for example, why a narrower aperture improves image quality, why resolution goes down when it improves image quality, and so on. Thank you very much!
One of my 7th grade students fiddling with the simple (glass) lens kits we had , came up a three lens arrangement. She said "It's not bigger (magnification) but it's clearer." Indeed it was. The Cooke Triplet came to mind, but I had to look it up. And indeed she basically rediscovered it. Really impressive. Cooke Triplets are from about 1890. Ansel Adams used them. Cooke Optics Ltd. is still in business in Leicester, UK making super high quality film and video lenses used in making feature films. Likely they've been part of most or all Oscars for Cinematography. In 2013 Cooke was awarded a special Oscar. As a professional still photographer I transitioned to a Nikon Digital SLR in about 2001. I thought I already had all the lenses I needed. All of the zooms I had that were good enough for film - junk. Unusable. My close up "Nikkor Micro" lenses 55mm and 65mm were still good. My 20mm good enough. I had to replace the zooms. (Even the 'consumer grade' zoom on my cheaper Nikon DSLR was better than any film zoom I'd ever had.) Some of the new digital zooms have huge focal length ranges. They were sharp but distorted on either side of the middle of their focal length range. Photoshop and Lightroom made easy work of this. Lightroom, knowing the metadata from the camera, automatically corrected distortion and any red-blue fringing, for whatever in between zoom focal length the lens had been set at. I did a lot of vertical shift when I used view cameras. There are '35mm' lenses that do this, but editing, even on my iPhone does a much better job.
@@IMSAIGuy Adams had good lenses. Probably no blur spots. He used color filters to lighten and darken colors, yellow,orange, red for skies, green to lighten foliage. It's in his notes. But single color would solve a lot of fringe problems. Also red light is always softer than the other colors. Blue of course (or UV) is sharpest. This shows up in a negative of any size. I've printed old 4x5 negs from 'professionals', often their lenses had horrible blur spots, uneven distortion (one corner but not the others.) Over all softness. Mostly unusable. And darkroom enlargers. The Bessler 4x5 is one of the standards. Everyone of those was out of whack. The film plane wasn't parallel with the base (paper plane). I made a concentric mirror alignment tool and fixed mine. The fix was in between any possible screw adjustment you could make -- so inherently out of alignment.
@WillN2Go1 there is a difference in terminology between an optics engineer and photographer. the blur spot or MTF is at each spot grain of the image, not a soft region as you may be saying. yes he used the filter for artistic effect but the side benefit was lower color aberrations. I had a 4x5 and bessler enlarger also. oh, the good old days of locked in a small dark room smelling chemicals. I don't think the f/64 club worried about lenses anyway 😀
@@IMSAIGuy I think once those f64 guys did some tests they didn't use f64. It's usually softer than f32. Refraction. I had a good exhaust fan... Long hours. Books on cassette and then CDs... The Manuel Álvarez Bravo show at the Getty some years ago when he was in his 90s were all prints he'd just made. A lot of them were out of focus.
Interesting stuff at 7:17; it has never occurred to me that a given lens assembly has to be optimized around a particular wavelength. I guess this means that every assembly will naturally assume its own 'color,' or bias, by design, thus giving it a particular uniqueness. It's probably fair to guess that most general-use lenses should be calibrated around the wavelength that's most readily received by the human eye, which is some kind of bright green, and which would be the center of the bullseye for a lens designer, right? Oh, and sorry to poke at this--but given the topic, I do hope you 'see' the irony of presenting with auto-focus here. Great vid.
the lens designer chooses several frequencies of light (similar to RBG) with different weighting factors on each. so the lens is optimized for a particular range of color.
In the case of a phone camera lens, it seems sorta strange that a "field flattener" wouldn't be accomplished by software. Though the mathematics would be dense, it would still be much thinner than a physical apparatus.
I found this very informative and interesting, thank you. I recently did a BINDT CAT 1 IR thermography course, cat 1 being the starter level! I intended to dive deeper but are the lens makups very similar to photography lenses or is the thermal camera purely dependent on the sensor technology to achieve a desirable image? Guess I may need to do the Cat 2 course!!
I wish the illustration shown after the Cooke Triplets had not been shown with Red-Green-Blue inks. This could be misleading if a mind like mine tends to jump ahead and think immediately color aberration.
Remember that glass is also a capacitor- so for every lens element you add, you loose light and microcontrast… the best lenses have around 7/9 elements, and are primes
Now consider the trade offs for something like euv. Where they reduced the stack to just 7 reflexion lenses because it is so hard to refract the light without loss
So interesting ! I am searching for the specs of a Canon FD 85mm 1.8 lens in order to manufacture the front element. Do you have any clue where to find it ? I would be so grateful
You will not find any specs. They are secret. Most large camera companies have front elements for sale. especially for expensive pro lenses. Having a single element made would cost more than the lens is worth.
I think I found a new wormhole to dive into. Any advice on how to go about doing more studying of this type of stuff? Are there any companies that'd make the lens elements to order?
I would get the book Modern Optical Engineering by Warren Smith if you are interested in lens design. Yes there are prototype houses for lens elements. It is way too expensive for DIY stuff. you can get some generic stuff at places like Edmund Optics
For some reason, I was surprised by how complex even the webcam lens was. Is this level of complexity present in basically all camera lenses we see today, even the ones on cameras like the Fujifilm Instax, or a disposable Kodak camera?
I would expect to find an all plastic lens not far different from the cooke triplet. if really cheap (and bad) a one element plastic aspheric lens might do.
Interesting observation on "bending film." First, I wonder whether anyone has tried a film plane that is a section of the surface of a sphere rather than a section of the surface of a cylinder. Second, you mention it's not easy to curve silicon - agreed - but maybe one day it might become more practical. Surprised not to hear refractive index mentioned, but perhaps your target audience already knows this is why you'd use different kinds of glass in a design, or glue two pieces of glass together. Another interesting topic to cover - maybe you have already, I see this is #755!?!, is how focusing is achieved by moving groups. Liked and subscribed. NOTE: I'm not an IMSAI guy but I cut my computing teeth on a PDP-11. I remember toggling in the bootstrap program so I could load up software from a reel of tape. I think it was two-inch tape? Worked a lot more with standard magnetic tape for IBM machines, also paper tape and punch cards. I sort of feel I invented the macro! ;) I worked at a typesetting shop in the '80s, and we had typesetting machines that could record keystrokes to paper tape, including a stop code that would indicate the tape had been fully read. Our most complicated jobs were classified ads, so we'd be changing font (which were on circular wheels of film) over and over in a regular pattern so every classified ad would look the same. I realized I could put all those commands on a single piece of tape, and splice the ends together so it would run in a loop. So you'd press the Read button, type in the 'headline', press the Read button, type the body copy, press the Read button, and type in the VIN. We had a board to which we affixed dowels to hold the tape loops. Saved us a lot of time, and I think those loops of paper tape were macros. One time I took several handsfull of the little dots punched out of the paper tape and put it across the top of some of our machines as part of Christmas decorations. We were still finding those darn things inside all our equipment months and years later. Oops!
I watched a video a few years ago about how lenses are made. They mentioned that someone was experimenting with using a curved sensor and that that was the future. He said that they would have to redesign the lenses to work with it and you'd only be able to use lenses designed for it. But as you know, companies like to get existing customers into newer models. If they're willing to sell all of their gear to move to something totally new they might just leave and go somewhere else. You have to make it easy to adapt. Look at mirrorless for example. You can adapt your old mount lenses to the new mount and still move to mirrorless. And mirrorless cameras have made designing lenses better because the focusing point is closer to the sensor. Or at least I think it would be easier. I shoot Nikon so I mostly know about Nikon lenses. I know that the z lenses are sharper corner to corner than the old f mount lenses. There's little to no chromatic aberration or focus breathing with the new lenses vs the old lenses. There's less vignette. I think mirrorless cameras made curved sensors non essential.
the two glasses have different properties for different wavelengths of light. called an achromat: ua-cam.com/video/PxqhA37bKtI/v-deo.htmlsi=gxmvHBKzFqV_cNw4
I find your videos helpful, because I'm trying to design an eyepiece that magnifies the image of a camera viewfinder. I want to mount the eyepiece ontop of the viewfinder. A simple telescope doesn't do the job, because the aperture is too small and it cuts off some parts of the virtual image.
Nice, I just discovered this. Good video. Off the top of my head, two other famous cameras that use a curved film plane are Agfa Clack and Agfa Click. Of course these were just really cheap, essentially toy cameras with single element lenses (or at best an achromat) but pictures are sharp thanks to the curved plane. I still use my Click from time to time.
Which the lens optical design software you used to reverse engineer the design.can u do a video on lens rehousing.there is not much material available about rehousing.or suggest books or online material you know about it.This was one great video.thx
lens cad program: Zemax mechanical books: Opto-Mechanical Systems Design by Paul R. Yoder, Jr. Fundamentals of Optomechanics (Optical Sciences and Applications of Light) by Daniel Vukobratovich
3:40 your use of the word radius seems nonstandard here- which is to say you you seem to be using a specialized version of the word? Radius usually means distance from a circle edge to its center. What way are you using it here?
Coma is Vietnamese for vampire. When I was in Saigon in 1972, I went to a movie called Coma. Vampire. Except this vampire was a woman who wore white and played piano in the forest on her time off.
Great video! Has anyone explained how the focal lenght of a camera lens works? Like, where do you "fit" say 800mm of distance in a 800mm lens? Because most often, you cant, most lenses aren't even as long as their focal lenght. (Unless ofc there is some glass trickery involved)
![Lp. Сердце Вселенной #60 РОЖДЕНИЕ ЛОЛОЛОШКИ [Финал] • Майнкрафт](http://i.ytimg.com/vi/YoR0pAV9FVQ/mqdefault.jpg)
This is so much better than most videos about how lenses work. The other ones are frustrating because they just leave you with more questions.
Well said. Even my high school physics text book tell me one single convex lens can make a perfect image everywhere, like if your object is 2f from lens then you will get a perfect image on 2f.
I agree!
Yes, Lenses can be very complicated to design, on one of my many visits to the old Hasselblad Factory, I was told that the Zeiss Biogon 38mm 4.5 took a long time to design and calculate, the amount of A4 papers used for calculation was a stack of one meter high ! I had the Zeiss Mutar 2x teleconverter, after I told the folks at Hasselblad how good it was on the Zeiss Planar 110mm 2.0, they got very interested and wanted to learn more, later I was told that Hasselblad had bought a computer from Canada to calculate Lenses. Today all Lens makers use computer software to calculate Lenses, and Lenses today outperform all older Lenses.
What year was that? Sounds like it was before the microcomputer era.
"Today all Lens makers use computer software to calculate Lenses, and Lenses "
and today all businesses use word processor software...
@@JohnDlugosz I do not remember the exact year, late 1980´s or early 1990´s, but Hasselblad designed fx the teleconverters 1.4x and 2x with that software. Hasselblad followed my experience with the Zeiss Mutar 2x which I used on different Lenses, it worked really well on fx Zeiss Planar 110mm 2.0 T* F and Zeiss Tele-Tessar 350mm 4.0 T* F, so Hasselblad tested how good the software was by designing the teleconverters, the 2x Hasselblad converter was just as good as the Zeiss converter !
Clicked on the video thinking that this is the start to my journey of making the most compact 1.4 primes to be ever made. I’m just gonna stop while I’m behind.
Thank you for this. Just a historical note regarding the Cooke Triplet: it was designed and patented in 1893 (not the 1930's) by Dennis Taylor who was employed as chief engineer by T. Cooke & Sons of York, England. Its earlier provenance makes it the more remarkable.
Interestingly the Cooke Triplet was f/3.5. Still modern entry level DSLR lenses typically are f/3.5 (at the wide). Some traditions live long.
Cooke Triplet is also basis for all zoom lenses:
Moving center element in between outer elements changes its focal length.
But also aberrations change and are harder to control and it took until 1930s to get first zoom lens into production.
I noticed this too, and there are some other smaller errors. Also, he just misses so many points and sounds disorganized.
Most jewelers' loupes are Cooke triplets.
There seems to be no limit to the number of technology fields that you are great at explaining/teaching. I would have loved to have you as a teacher/professor IMSAIGuy. Thank you for making these videos for us fine sir! Fred
Another trick they've been doing recently for mirrorless cameras is that since you've got to apply digital processing to the sensor image's anyway, some corrections can be done in software and the lens design can be optimized for other factors. If you squint this is a analogous to the curved film trick you mention in the video.
I know they correct for distortion and cos4, not sure about focus
This is the best vedio on optical engineering. No one ever just gave this 15 min lecture...yiu are a god to me man
Ever since I learned about the principles of lenses and telescopes in middle school, I've always had this question: Why do these telescopes and camera lenses contain such complex lens assemblies? Now, at the age of 34, I finally found a satisfying answer in a random UA-cam video I clicked on. Thank you
Thank you. Yet ANOTHER field of interest that I have always had great interest in.
Your experience and expertise is seemingly endless.
Thanks.
Hey, just wanted to say thanks a ton for teaching in such an awesome way. You made those tough concepts a breeze to grasp.
Great to hear!
Really interesting. I've been a photographer for decades, and I'm a little ashamed to say that however mind-boggling I always found lens techniques to be, I know way too little about the 'glass' that I use. Thanks and thumbs up.
I have an Astro-Physics apochromatic triplet, with the 3 lens elements in contact with each other and oil spaced to reduce internal reflections, and improve transmission. I love this thing! For as much as it costs, the field flattener accessory comes with quite a breathtaking price tag; but it was intended for medium format film photography at the focal plane. Fortunately, at the time I acquired it, only APS-C sized CCD devices were practical (affordable!) and the part of the focal plane I was using was "flat enough".
Later I move to using a Riccardi-Honders astrograph, an f/3.8 optical system and quite a novel design. You might mistake it for a Schmidt-Cassagrain but it's actually more like a folded refractor with a rear silvered lens, and more importantly, I believe all spherical lens figures. And a nice, large and wide flat focal plane! Only suitable for astrophotography, but that's the problem I had. Never had an eyepiece in it. I asked the designer of that telescope why he didn't use carbon fiber or some other material with low coefficient of expansion due to temperature for the tube assembly, rather than aluminum? That was a deliberate choice, the dimensional change of the tube due to temperature offset the changes in the optical elements as they also cooled down. There is quite a bit of "art" to go along with the science. Difference between theory and practice and all that stuff you learn the hard way.
Optics are cool! Really nice optics are very cool and expensive! And definitely one of those fields where there's no single "best" tool/design. It's always a tradeoff over a bunch of factors, including $$$ it seems.
very few people on the planet can do a good job of optomechanical design.
Very cool. I've wondered about this, off and on, for decades and never got around to looking it up! One thing I *think* might be missing is that you can use materials with different indexes of refraction for each lens to tweak it even more.
yes, glass with different dispersion, to correct for color aberrations. classically referred to as crowns and flints. I talk about it a little: ua-cam.com/video/PxqhA37bKtI/v-deo.html
Likewise. Interesting to note that the more glass elements you have in a lens, the worse the image quality. It goes something like this: more glass = less light (in terms of F stops.
@@chawenhalo0089 That was true before the development of lens coatings which have been improved to a point that I think 99% of light is no longer lost now due the reflection at each element. This is why before lens coatings many classic designs were limited to not many elements 3 to 5.
@@dwaynepiper3261 😅 I ain't that old! Was thinking about the difference between Nikkor "D" series lenses compared to AFS. I get far cleaner images (depth of field, chromatic aberrations) on my old 80-200mm than on the far easier to use AFS 70-200mm (the latter being noticeably sharper when croping); both 2.8. Horses for courses as they say... That's purely down to element count... and me romanticising of course.
@@chawenhalo0089 Neither am I but I like to understand how technology progressed to where it is today.
Could you comment on how different colours/bandwidths are reconstituted/merged?
In most of your diagrams it appeared to show different colours focusing at different points. Thanks!
What you mean 'bent the film into a cylindrical section' ? That only helps with the one axis. Wouldn't it need to stretch the film into a spherical section to provide axially-symmetric non-planar focal surface?
yes that would be better but the bend is just in the long part of a rectangle so helps a little but not everywhere
Enjoy this video because I’ve always been fascinated by optics. And it is definitely a mathematical situation. Zeiss took the triplet and turned it into the Tessar , which has certainly stood the test of time as well. Thank you for sharing your thoughts here because it is truly a fascinating video. I look forward to seeing more of these and sharing your knowledge with us layman. In order to get a flat image the curvature of one lens has to be similar to the other to cancel out the curvature of the other lens. That’s why lenses became symmetrical to cancel the curvature of the other lenses. The hologon lens by Zeiss is a good example of this like two opposing marbles cut in half. The Japanese did the same as you, cut the old lenses in half and reverse engineered them and actually eventually made improvements on the Planar and Zenitar designs which many of their lenses (Nikon) are designed after.Regards Gerry
Fascinating... Well done. I really learned a great deal. Thanks for taking time to do this for us.
This is the easiest to understand summary of optical design I’ve seen on UA-cam.
Very educational. Thank you for sharing. Still… I am puzzled on how focussing works. What happens during the turning of the focus ring, and why?
It moves the lens group closer or father to the film
"The Cooke triplet is a photographic lens designed and patented in 1893 by Dennis Taylor who was employed as chief engineer by T. Cooke & Sons of York".
I just came to check what the elements and groups mean in lenses... Ended up watching the whole video and learnt so much!
Thanks, Time has never been that fast. So enjoyable to watch and learn
love that you included a photolitho example
2:20 Is that why on telescope (doublets, almost like one convex lens) need a field flattener to focus the corners of the image, or is that another thing?
same
This is really interesting.. Wide angle lenses are hard to design for, makes sense getting the focal plane flat is the hard part, that's my walk away. I wonder about 600mm lenses at f4 costing $15,000 for like a Sony camera system, is that the cost of materials?
Very interesting, thanks. That field flattener looks a bit like a Schmidt plate. Am I on the right track?
They look similar but are quite different. The Schmidt plate is at the aperture stop of the system. There is a Fourier transform from the aperture to the image. the image is in x-y space and the aperture is in angle space. The incoming wavefront will be phase corrected by the plate to correct for spherical abberation and I think astigmatism and coma. it is difficult to grind an aspheric mirror so the job is given to a thin piece of glass that can be warped, ground flat, and unwarped to result in the shape.
@@IMSAIGuy Thanks for the explanation. I'ii have to try and find out a bit more about this topic.
this explains pretty well tho why it took a (comparatively) long time for compact cameras to gain lenses that went wider than 35mm (equiv.)
guess it's just that - harder and more expensive to make light bend around alot more at wider angles
Great work Sir ! there is so much to learn. Gone through your channel, quite inspirational, started really loving what you're doing. Thank you so much.
Fascinating stuff! Thank you! I wish there were more videos on UA-cam about optics and optical design.
I could teach you how to do lens design and loose all my viewers. They only care about RF. In silicon valley I can count the lens designers on one hand. My buddy in San Diego designed one of the mars rover lenses. He is quite proud.
Fully agree that their should be more exellent youtoube video's like this about optics. Maybe a second channel for optic geeks only?
@@IMSAIGuy I’m one of those lens designers in Silicon Valley. There are more of us these days, but not that many good ones. 😁
Different focus, but @HuygensOptics makes interesting videos
The Cooke triplet actually dates back to 1883. So it was already half a century old by the thirties.
11:43 How did they attach fiber plate to the sensor ? Is it glued ?
Probably. There are many optical glues.
@@IMSAIGuy Similar configuration is used in a electron microscope. It has almost an ordinary sensor but with bonded fiber glass and ndyag scintillator plate. Maybe you could do some research how it is bonded ? This way a microscope could be done in a very cheap manner.
www.edmundoptics.com/c/adhesives/644/
cheap way is to use 'G-S Hypo Cement '
Great video, I always wondered about this! What's the reason they can't make a curved sensor for the camera?
cost
I have numerous text volumes on optical design all very interesting to read and yes specialist lenses are incredibly complex. Thank you for a fascinating rundown on camera lenses. I particularly enjoyed the end bit about lens design for phone cameras.
Once again, many thanks for the great info.
At 06:50
Yes, the use a lot of elements for a single lens. More so if you consider that they use a very narrow band UV light source. Chromatic aberration is therefore limited,
EDIT: Good to see that you mention it also.
Incredibly educational. I'm new to the camera hobby. (3 years). And was curious to find an explanation. Thank you.
That was nicely done.... Thank you for your time
I randomly came across this video in my feet and it’s super interesting. Do you have any explanations as to why wide angle lenses get longer as you zoom wider? It feels like if I am increasing my field view lens should be getting shorter but the front element always goes farther from the sensor and I don’t understand why.
sorry, too complicated to say in a few words
Very interesting explanation. Always wondered what a field flattener does to light. Thanks for sharing.
11:45 they also use this for another effect, the fibers aren't actually straight thru, instead they're all twisted up to turn the image right side up.
This is so cool! Thanks for sharing. I believe the optical coating is also important, isn’t it to ensure the light entering the lens is within its comfortable zone (generally using thin film reflection to bounce back the other ones)
coating does two things
1. increases the light transmission.
2. decreases stray light reflections
Where I can bay the lens? is the question?
lots here: www.edmundoptics.com/contact-support/catalogs/
@@IMSAIGuy Thanks!
Thanks for the clear explanation of why we need so many layers of lens in cameras. I have a stupid question, I am wondering why our eyes can do it so good with only one lens? Is the lens in our eyes any special?
ua-cam.com/video/wZ1dcruxYR0/v-deo.html
Thanks for the video! One additional complication is that adding elements isn't "free" in terms of optics: it can worsen problems like lens flare.
It can help also if you are experienced and add flare stops.
11:52 the fiber plane reminds me of a mineral called ulexite, also known as "TV rock". Would it be possible to make a fiber plane out of this mineral?
Such a fine in-depth video! Thank you Sir 💖
Thankyou! Could you suggest how one gets more coma in a simple cooke design?
more off axis astigmatism
Awesome job. Can you share the prescription you recovered from that last sectioned lens?
that was decades ago
it is a type of Zeiss Sonnar
@@IMSAIGuy Thank you, Sir!
well explained! could SLR or DSLR lens designers use the cell phone field flattener lens type to make a minimalist sise lens for full frame cameras? too hard to grind complex shape in bigger lenses?
Field flatners have been used for 100 years
I would be interested in more videos like thsi, i have been trying to research building a triplet telescope for a while but i havnt found any triplet sets so the idea is to find out how to select individual elements, problem is nobody actually explains it well at all.
Are there any open source tools for this? Or any actually useful resources?
I would get the book Modern Optical Engineering by Warren Smith if you are interested in lens design.
CAD tools I've used: ZEMAX, OSLO, Code V, LightTools. once in a while MATLAB or Octave for specialized calculations and color theory. OLSO may have a trial version, you can also try WinLens3D
How eyes produce high resolution image with just cornea and one lens?
ua-cam.com/video/wZ1dcruxYR0/v-deo.htmlsi=zmnkN9-E5hmBH8wP
Is the Field Flattener the same in Astro photography?
So cameras need several lenses becasue the sensor is flat?
And eyes need only one because the retina is semicircular?
7:16 This style of cheating was also good for black and white photography, in that since your photosensitive medium will only provide you with shades of grey, you don't need to expose it to all the colours of the spectrum.
So with black and white photography you could address the problem of a lens with poor chromatic aberration, by using a red, green or blue filter when taking the photo.
Whack a red filter onto the front of your lens and now the blue and green light that is causing blurriness on contrasty edges, is gone.
Get yourself some really nice darkness for blue skies too, to make those white clouds pop!
Edit, never mind, you mentioned this! LOL
The current 80s night vision design is I think a 7 piece direct to the PC. The PC to anode phosphor screen assembly is proximity focused onto that FOB which may be inverting. The objective is blue blocked to deal with CA.
Fascinating. Thanks for sharing
So why is the Cooke's tripplet not enough?
Super interesting, thanks for posting.
I like the aperture logo
Where do I start if I want to measure a lens and figure out its parameters? I have a huge aerial photography lens, the first element is nearly 6 inches in diameter, and aside from focal length and aperture, I'm a bit in the dark. The front and rear halves unscrew from the shutter (no adjustable aperture, just open-close). Taking a giant lens spanner to the front, it's just two elements. The rear has 3 elemens, one single and two glued together. Since it's fixed focus as well, I'm pondering how to make it adjustable focus - the easy answer might be to mount the lens on a rack / bellows type movement, but I've been testing it out on the kitchen counter using a sheet of paper to gauge the focus and a ruler to see how much movement is required, and for the range of distances I'd like to use it at, I need over a meter of travel. The bellows would be bigger than the camera and require some support to keep out of the optical path. Just for fun, I calculated the hyperfocal distance and its around a mile.
that is a very complicated process. you need to measure the curvatures of each surface and the thicknesses and spaces, then you will need to know what glass type is used for each element (index and dispersion). these will all require special instruments. once you have these number they will not be accurate enough. you will need to put them in an optics design program to adjust them.
could you recommend some books on how to design and calculate these lenses?
I would get the book Modern Optical Engineering by Warren Smith if you are interested in lens design.
CAD tools I've used: ZEMAX, OSLO, Code V, LightTools. once in a while MATLAB or Octave for specialized calculations and color theory. OLSO may have a trial version, you can also try WinLens3D
@@IMSAIGuythanks a lot!
That's really interesting how you explain how lenses is working, so most people can understand, or at least have an idea about it.
I subscribe to your channel because you have a lot of good interesting content.
Greetings from Kenneth (Denmark)
Great presentation! Thank you!
I have a Cooke Triplet design lens. An old Meyer Optik Domiplan. Modern lenses actually use too many elements IMO. Most modern photographers only care about sterile perfection in lenses. The older Leica Summicrons only used six elements with a Double Gauss design. Not sure about the newer ones.
Great video.
At 2:22 coma is Latin for comet iirc. Goes all the way back to Galileo era star gazing.
3:14 I believe Cooke 'tool inspiration' for that design from the Chermans.
4:04 T1&2 are important, historically, T3 onwards are junk and to be forgotten. That's when James Cameron was no longer involved.
4:16 Radiuses? Radiiii?
4:40 Triplet, tri, tre, more latin.
10:57 There are curved sensors, I'm not aware of any that have been used in mass produced devices though. If curved sensors do exist in cameras, we can purchase, probably mated to fixed lens (non interchangeable) and probably of a fixed focal length.
Fun Fact; nothing can correct for the obvious aberrations in my personality.
Very interesting! I'd also like to learn about aperture, for example, why a narrower aperture improves image quality, why resolution goes down when it improves image quality, and so on. Thank you very much!
One of my 7th grade students fiddling with the simple (glass) lens kits we had , came up a three lens arrangement. She said "It's not bigger (magnification) but it's clearer." Indeed it was. The Cooke Triplet came to mind, but I had to look it up. And indeed she basically rediscovered it. Really impressive.
Cooke Triplets are from about 1890. Ansel Adams used them. Cooke Optics Ltd. is still in business in Leicester, UK making super high quality film and video lenses used in making feature films. Likely they've been part of most or all Oscars for Cinematography. In 2013 Cooke was awarded a special Oscar.
As a professional still photographer I transitioned to a Nikon Digital SLR in about 2001. I thought I already had all the lenses I needed. All of the zooms I had that were good enough for film - junk. Unusable. My close up "Nikkor Micro" lenses 55mm and 65mm were still good. My 20mm good enough. I had to replace the zooms. (Even the 'consumer grade' zoom on my cheaper Nikon DSLR was better than any film zoom I'd ever had.)
Some of the new digital zooms have huge focal length ranges. They were sharp but distorted on either side of the middle of their focal length range. Photoshop and Lightroom made easy work of this. Lightroom, knowing the metadata from the camera, automatically corrected distortion and any red-blue fringing, for whatever in between zoom focal length the lens had been set at.
I did a lot of vertical shift when I used view cameras. There are '35mm' lenses that do this, but editing, even on my iPhone does a much better job.
Ansel's Cooke probably worked fine since he had 8x10" film so could have large blur spots and used a red filter to get rid of any color aberrations.
@@IMSAIGuy Adams had good lenses. Probably no blur spots. He used color filters to lighten and darken colors, yellow,orange, red for skies, green to lighten foliage. It's in his notes. But single color would solve a lot of fringe problems. Also red light is always softer than the other colors. Blue of course (or UV) is sharpest. This shows up in a negative of any size.
I've printed old 4x5 negs from 'professionals', often their lenses had horrible blur spots, uneven distortion (one corner but not the others.) Over all softness. Mostly unusable.
And darkroom enlargers. The Bessler 4x5 is one of the standards. Everyone of those was out of whack. The film plane wasn't parallel with the base (paper plane). I made a concentric mirror alignment tool and fixed mine. The fix was in between any possible screw adjustment you could make -- so inherently out of alignment.
@WillN2Go1 there is a difference in terminology between an optics engineer and photographer. the blur spot or MTF is at each spot grain of the image, not a soft region as you may be saying. yes he used the filter for artistic effect but the side benefit was lower color aberrations. I had a 4x5 and bessler enlarger also. oh, the good old days of locked in a small dark room smelling chemicals. I don't think the f/64 club worried about lenses anyway 😀
@@IMSAIGuy I think once those f64 guys did some tests they didn't use f64. It's usually softer than f32. Refraction.
I had a good exhaust fan... Long hours. Books on cassette and then CDs...
The Manuel Álvarez Bravo show at the Getty some years ago when he was in his 90s were all prints he'd just made. A lot of them were out of focus.
Interesting stuff at 7:17; it has never occurred to me that a given lens assembly has to be optimized around a particular wavelength. I guess this means that every assembly will naturally assume its own 'color,' or bias, by design, thus giving it a particular uniqueness.
It's probably fair to guess that most general-use lenses should be calibrated around the wavelength that's most readily received by the human eye, which is some kind of bright green, and which would be the center of the bullseye for a lens designer, right?
Oh, and sorry to poke at this--but given the topic, I do hope you 'see' the irony of presenting with auto-focus here. Great vid.
the lens designer chooses several frequencies of light (similar to RBG) with different weighting factors on each. so the lens is optimized for a particular range of color.
I wish you had covered the Tessar lens.
just a triplet with an achromat back element.
But it’s a great lense.@@IMSAIGuy
In the case of a phone camera lens, it seems sorta strange that a "field flattener" wouldn't be accomplished by software. Though the mathematics would be dense, it would still be much thinner than a physical apparatus.
I found this very informative and interesting, thank you. I recently did a BINDT CAT 1 IR thermography course, cat 1 being the starter level! I intended to dive deeper but are the lens makups very similar to photography lenses or is the thermal camera purely dependent on the sensor technology to achieve a desirable image? Guess I may need to do the Cat 2 course!!
resolution of thermal cameras is low compared to film or CCD. so lenses are simple (one element). they are also made of exotic material (Germanium).
Paper, pen, a scratched wooden board, a clearly not very young man's hands, and a spool of copper wire slightly off the screen... this will be good!
I wish the illustration shown after the Cooke Triplets had not been shown with Red-Green-Blue inks. This could be misleading if a mind like mine tends to jump ahead and think immediately color aberration.
This was absolutely fascinating
Remember that glass is also a capacitor- so for every lens element you add, you loose light and microcontrast… the best lenses have around 7/9 elements, and are primes
Now consider the trade offs for something like euv. Where they reduced the stack to just 7 reflexion lenses because it is so hard to refract the light without loss
VERY GOOD AND QUICK LENS EDUCATION !
So interesting ! I am searching for the specs of a Canon FD 85mm 1.8 lens in order to manufacture the front element. Do you have any clue where to find it ? I would be so grateful
You will not find any specs. They are secret. Most large camera companies have front elements for sale. especially for expensive pro lenses. Having a single element made would cost more than the lens is worth.
Fantastic explanation. Would love to see more!
This is absolutely amazing thank you! I am in awe
I think I found a new wormhole to dive into. Any advice on how to go about doing more studying of this type of stuff? Are there any companies that'd make the lens elements to order?
I would get the book Modern Optical Engineering by Warren Smith if you are interested in lens design. Yes there are prototype houses for lens elements. It is way too expensive for DIY stuff. you can get some generic stuff at places like Edmund Optics
Wow! Very cool! Always wondered why so many lenses!
For some reason, I was surprised by how complex even the webcam lens was. Is this level of complexity present in basically all camera lenses we see today, even the ones on cameras like the Fujifilm Instax, or a disposable Kodak camera?
I would expect to find an all plastic lens not far different from the cooke triplet. if really cheap (and bad) a one element plastic aspheric lens might do.
@@IMSAIGuy That makes sense. Thank you for answering my question. This was a really informative video!
Interesting observation on "bending film." First, I wonder whether anyone has tried a film plane that is a section of the surface of a sphere rather than a section of the surface of a cylinder. Second, you mention it's not easy to curve silicon - agreed - but maybe one day it might become more practical.
Surprised not to hear refractive index mentioned, but perhaps your target audience already knows this is why you'd use different kinds of glass in a design, or glue two pieces of glass together.
Another interesting topic to cover - maybe you have already, I see this is #755!?!, is how focusing is achieved by moving groups. Liked and subscribed.
NOTE: I'm not an IMSAI guy but I cut my computing teeth on a PDP-11. I remember toggling in the bootstrap program so I could load up software from a reel of tape. I think it was two-inch tape? Worked a lot more with standard magnetic tape for IBM machines, also paper tape and punch cards.
I sort of feel I invented the macro! ;) I worked at a typesetting shop in the '80s, and we had typesetting machines that could record keystrokes to paper tape, including a stop code that would indicate the tape had been fully read. Our most complicated jobs were classified ads, so we'd be changing font (which were on circular wheels of film) over and over in a regular pattern so every classified ad would look the same. I realized I could put all those commands on a single piece of tape, and splice the ends together so it would run in a loop. So you'd press the Read button, type in the 'headline', press the Read button, type the body copy, press the Read button, and type in the VIN. We had a board to which we affixed dowels to hold the tape loops. Saved us a lot of time, and I think those loops of paper tape were macros.
One time I took several handsfull of the little dots punched out of the paper tape and put it across the top of some of our machines as part of Christmas decorations. We were still finding those darn things inside all our equipment months and years later. Oops!
Really awesome and very very clear explanations! That's some serious nerding out - this is the content that we need! Instant subscribe from me.
Bend Digital Sensors can be made to simplify the lense construction.
Thank you very much for all the information and details, very well explained, it would be great to find more videos like this.
How do the cameras bend the film? It's easy to bend it to make a cylindrical surface, but we have to bend it to make a spherical surface, haven't we?
I watched a video a few years ago about how lenses are made. They mentioned that someone was experimenting with using a curved sensor and that that was the future. He said that they would have to redesign the lenses to work with it and you'd only be able to use lenses designed for it. But as you know, companies like to get existing customers into newer models. If they're willing to sell all of their gear to move to something totally new they might just leave and go somewhere else. You have to make it easy to adapt. Look at mirrorless for example. You can adapt your old mount lenses to the new mount and still move to mirrorless. And mirrorless cameras have made designing lenses better because the focusing point is closer to the sensor. Or at least I think it would be easier. I shoot Nikon so I mostly know about Nikon lenses. I know that the z lenses are sharper corner to corner than the old f mount lenses. There's little to no chromatic aberration or focus breathing with the new lenses vs the old lenses. There's less vignette. I think mirrorless cameras made curved sensors non essential.
What a great video, I enjoyed watching it.
Thanks for your explanation!
This video is a gem
Why glue glasses together instead of cutting one with the shape of the two?
the two glasses have different properties for different wavelengths of light. called an achromat: ua-cam.com/video/PxqhA37bKtI/v-deo.htmlsi=gxmvHBKzFqV_cNw4
Thank you very much for the explanation. I knew there had to be a reason for something that's been done for decades.
Enjoyed watching n listening a lot
I find your videos helpful, because I'm trying to design an eyepiece that magnifies the image of a camera viewfinder. I want to mount the eyepiece ontop of the viewfinder. A simple telescope doesn't do the job, because the aperture is too small and it cuts off some parts of the virtual image.
Nice, I just discovered this. Good video.
Off the top of my head, two other famous cameras that use a curved film plane are Agfa Clack and Agfa Click. Of course these were just really cheap, essentially toy cameras with single element lenses (or at best an achromat) but pictures are sharp thanks to the curved plane. I still use my Click from time to time.
Which the lens optical design software you used to reverse engineer the design.can u do a video on lens rehousing.there is not much material available about rehousing.or suggest books or online material you know about it.This was one great video.thx
lens cad program: Zemax
mechanical books: Opto-Mechanical Systems Design by Paul R. Yoder, Jr.
Fundamentals of Optomechanics (Optical Sciences and Applications of Light)
by Daniel Vukobratovich
@@IMSAIGuy Thanks you
I have been looking for this for sooooo long!
3:40 your use of the word radius seems nonstandard here- which is to say you you seem to be using a specialized version of the word? Radius usually means distance from a circle edge to its center. What way are you using it here?
Same. Each surface is a part of a circle.
Coma is Vietnamese for vampire. When I was in Saigon in 1972, I went to a movie called Coma. Vampire. Except this vampire was a woman who wore white and played piano in the forest on her time off.
Do these designs get patented or otherwise protected? It seems fairly easy for a competitor to copy a well made design.
yes, they get patented. But a clever designer can change a few things and usually avoid any problems.
Great video!
Has anyone explained how the focal lenght of a camera lens works? Like, where do you "fit" say 800mm of distance in a 800mm lens? Because most often, you cant, most lenses aren't even as long as their focal lenght.
(Unless ofc there is some glass trickery involved)