Meet The Gaffer #28: Using A Light Meter - Part 1
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- Опубліковано 25 лис 2016
- Director of Photography, Tomas Tucker, shows how you can determine the real ASA/ISO of your camera by using a light meter and white card.
I think Zahi has discovered a mistake I made in my presentation. At about 5:55 into Part 1, I mention that if the camera’s f-stop reads f/4 and the light meter reads f/2.8, your camera is slower than 400 ASA. This is incorrect. You need to increase the ASA on your meter to 800 to get it to read f/4. DON’T TOUCH THE F/STOP ON THE LENS! Your camera is telling you what f-stop the meter should be reading and you adjust the light meter’s ASA ’till you get there. I misspoke. I should have said, “Your camera is faster and the native ASA is 800”. - Фільми й анімація
Great things, especially about exposing LOG. I had no idea that there was a chart like this, thank you!
This is so informative, man !!! This is what I've been searching for ages, top secret stuff , thanks for sharing
Ha, ha! Glad you found us:)
Greta piece of information. Thank you, Luke and Tomas.
Loving "Meet The Gaffer" so naturally I subscribed right away ! Thank You !!!
wakeup1986, welcome to the party!
The link below will take you to two documents:
1. How to determine the ASA of your camera
2. A LOG Values Chart
www.dropbox.com/sh/u144stotjq0o8a5/AABezpKwpDt-FvRdb4n7sHsya?dl=0
Thanks for making this !
Thank you for such a helpful video!
I just recently filmed a music video and underexposed while shooting in log lucky it is still usable. This information is great and will help a lot in future shoots.
I like the idea of the proper as a of the camera.. I've been calibration the meter to the camera basically the same only different.
This one 's an eye opener....But should we trust the waveform monitor for reference !
This is excellent, my dad has one and borrowing it tomorrow to test, I have a G7 and while not amazing it's really capable of what I want to do. That said i want to make sure i get the right exposure and i feel even with monitors it's not that quick to communicate and learning this is invaluable
Is there a link to the document still available?
Thanks for all these great videos, BTW! So much solid information packed into short, easy to watch videos.
If the original link does not work, try this: www.dropbox.com/sh/u144stotjq0o8a5/AABezpKwpDt-FvRdb4n7sHsya?dl=0
Also calculate in that many rec709 curves do highlght compression (knee, filmgamma, hypergamma). That screws up your 90% white object vs the waveform value.
I found its a good idea to match a greycard , whitecard and compare wfm levels with both
Ulrich Mors you can’t expose a white card at 100 ire for rec 709. Where is your knee? If you set it at 90, everything above it will get compressed. You expose the white card at 90 ire. He is doing it wrong.
Checked with Sony 7SII and Dsc Labs chart 90%white got exact match on lightmeter and camera settings, well done sony.
:)
I'm showing a 2-1/2 stop difference. Is that possible?
I've always wondered how you can identify precise IRE values, e.g. 59 or 61 as opposed to 60. I have a canon c100 and a smallHD 502...am I missing something? Thanks!
Andrew,
You’re right, it’s very difficult to determine exact values on a waveform monitor, especially on something like the SmallHD 502. If you can expand the waveform monitor to full screen it can help. You just do the best you can. Looking at the luminance channel only can make it easier. On more sophisticated WFM’s, like ones from Leader or Tektronix, you can actually select one line of video and find the exact IRE level of that line. On these very expensive monitors the graduated scale is precisely marked and you can illuminate the scale to your preference which makes reading accurate measurements easier. For the moment, with the equipment you have, you can do a reasonable job of “guestimating” the approximate IRE value. If you’re off by a digit or two, especially in log, you’ve got plenty of signal to work with. This is one argument for slightly over exposing your log footage. Many people feel it yields a superior image. Again, testing is the key.
Best of luck, and keep testing & taking notes!
Tomas Tucker
Hey again Luke, been trying to find that word document mentioned a couple of times in the vide by Tomas. Is it uploaded somewhere? Thanks.
www.dropbox.com/sh/u144stotjq0o8a5/AABezpKwpDt-FvRdb4n7sHsya?dl=0
In the demonstration, the camera is at f/4 with correct exposure, when the meter reading shows only f/2.8. So the camera has to be a step faster right? Tomas says it's a step slower.
Yes, I believe that’s correct. It’s been a few years and I remember there was one slip, but I should go back and note it in the comments. Thank you.
To me it makes sense Red not publishing an ISO (I own a Sony but have shot Red and many other cameras).. because there are different ways of treating an ISO 'value' - for example a camera might have 12stops of LAT and at 800 you have 6 headroom above midgrey and six below, shoot the camera (set to 800) at 400 and you have 5headroom/7shadow, or 1600 and get 7headroom/5shadow. In post you push pull the gamma so your mid is at mid. Now either of the three exposure options will render different results, mainly cleaner shadows/less headroom (good in a controlled situation like a studio) or dirty shadows/more headroom (good in a midday set with no huge lights to fill) so IMO the DP will be swinging the 'ISO' all the time, or certainly project by project. To some extent prebuilding LUTs and boarding the desired LUT make this clearer to those doing post..
My experience of Slog3 on sony is that the published figure is very low.. giving a 'great' sales spec of native 2000 and awesome highlight retention.. but actually a noisy mash of a file.. (Id certainly open up 2 or meter at 800) so maybe it is simpler just not to publish an ISO.
My experience as well.
On the basis of the hypothetical example you gave over the REC709 part, would it imply that the camera's ASA is actually faster (higher) than what you've set it at (which is ASA400)? Again, in the hypothetical example; you set the camera at ISO 400 and the 90% white peaked at 100 units at f/4.0 -- if the meter read the incident light (with the same settings) at f/2.8, which is one stop faster, would it then mean that at those settings it would actually need an extra stop of light? Which would mean that the camera's ISO is actually 800 when you've supposedly set it at ASA400?
Would that be the conclusion? Just trying to wrap my head around everything as I'm relatively new to this. Hopefully my wording isn't too confusing. Cheers.
Here’s Tomas’ response to your question:
Zahi, thanks for the question. This whole business of “native ASA (or ISO)” is very confusing and I think you’ve caught a mistake I made in the presentation. I said your camera is slower when I should have said FASTER. It’s your camera that’s telling your light meter what the correct ASA is, not the other way around. Thank you! Let me see if I can clarify. We talked about setting up a white reference card & putting a light source on it. Then we set the camera’s ASA to what the manufacturer recommend as the “native” ASA. Let’s say that’s 400 to follow the example in the clip. Using a waveform monitor, adjust the f-stop on the lens to get 100 units on the waveform. Now, set your meter to 400ASA and see if the stop that reads on the meter matches the f-stop on your lens. If they don’t match, adjust the ASA on the meter until the f-stops match. Let’s say your camera lens registers f/4 to get the 100 units on the wfm. If the light meter reads f/2.8 at 400ASA your going to have to INCREASE the ASA to 800 to get the light meter to read f/4. So, the “native” ASA of your camera is 800. Thanks for catching that error, I will have Luke make a correction on the clip. Good luck to you, get comfortable with your light meter and happy shooting.
Please let me know if this clears it up.
Luke Seerveld thanks for being the middle-man on this :)
Tomas, thank you for your answer. Your videos (and reply) have been quite useful to me as I'm about to buy my first light meter (Sekonic 858). Do you mind giving a look at the following questions and/or conclusions? They’re a handful and I don’t expect answers to all of them at all, however any information would be of great help.
I’m just recently getting into cinematography, my background is in directing.
1- Defining the camera’s real native ISO is important to cinematographers as that is the signal at which the camera will have the best noise to dynamic range performance. It doesn’t mean there won’t be noise, but it means it’ll have the best balance between clean noise and high dynamic range, usually equally distributed amongst shadows and highlights.
2- In the video you mention setting the camera at the desired shooting ISO, and in your comment you suggest setting it at the manufacturer’s claimed native ISO. Just to make sure, were you assuming that the desired shooting ISO would match the claimed native one?
3- So now you know the camera’s real native ISO. Then what? How does it help you? It seems to me that at the end of the day, in digital, you have to choose between more highlight latitude (by increasing signal gain/ISO) for less DR in shadows and more noise. OR, less noise at a low ISO with a higher risk of clipping. Do you agree with this?
4- When you say “normal exposure” in the video. Is that when middle-gray is at 50% of the waveform? If not, what do you mean by “normal exposure”?
5- I took a lighting workshop and it was recommended that we have our light meters themselves sent off to calibration (every 6 months or so). How necessary is this? I live in the Middle-East and there’s no way for me to calibrate a light meter. How much of an issue is this? I’m getting a light meter precisely because I need a steady way to measure light and train my eye to see better- if that instrument is not precise and stable, doesn’t it defeat the whole purpose of it?
Thanks again!
I’ll forward these on and we’ll see if Tomas has a moment to respond:) Meanwhile, all the best in you cinematographic pursuits!
I have a question: Are you sure the its the digital sensors that have inaccurate ISO values or the lenses? Because I know for sure the f-stops are not T-stops and are pretty inaccurate on the photgraphic lenses.. How would I know how to calibrate the ISO if the lenses is inaccurate as well? I need cine-lenses to calibrate, right?
Hiski Hämäläinen, this is from Tomas:
Hiski,
You bring up an interesting point and one that I had not considered in thinking about my light meter demo. It’s true that there can be a substantial difference between the f-stop and the t-stop of some lenses, as much as half a stop. One would think that when camera manufacturers are calibrating their equipment they are probably using excellent quality lenses that are measured in t-stops. If you take that same camera and operate it with a lens that has a low transmission factor, it could indeed alter the apparent camera sensitivity, or ASA. In this case it’s unfair to blame the manufacturer for the discrepancy, it’s caused by the lens. However, the ASA calibration still makes sense for you to truly understand the effective ASA of your camera given all the various additional equipment you will be using to shoot a project. It’s important for you to know that the meter readings you are taking in the field have a direct relationship to the f-stop or t-stop on your camera. And, yes, you really do need cine lenses or high quality still lenses with a very high transmission factor (minimal loss through the lens) to get an accurate read on your camera’s native ASA. Thanks for the comment.
On Nov 27, 2016, at 8:00 AM, Luke Seerveld wrote:
Hi Tomas,
Could you field this question?
Luke Seerveld
415.860.6365
Begin forwarded message:
From: UA-cam
Date: November 27, 2016 at 3:04:51 AM PST
To: lseerveld@gmail.com
Subject: New activity on your video: Meet The Gaffer #28: Using A Light Meter - Part 1
Reply-To: UA-cam
New comment on your video
Meet The Gaffer #28: Using A Light Meter - Part 1
Hiski Hämäläinen
I have a question: Are you sure the its the digital sensors that have inaccurate ISO values or the lenses? Because I know for sure the f-stops are not T-stops and are pretty inaccurate on the
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Tomas Tucker
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tomas@tomastucker.com
Thanks for the answer! I am always looking forward to new episodes on your channel! Make a t-shirt or something and I will buy one :D
Hiski Hämäläinen, send me your address and I'll send you a T-shirt. info@seerveldmedia.com
Luke Seerveld I’m very confused. I use a Zeiss 55mm 1.8 lens, a lens measured in f/stops. Does this mean I won’t get an accurate reading of what my native ASA is because I am not using a high quality cine lens?
I won’t be able to answer that question as well as Thomas or perhaps another DP here, but you should be able to get close with a quality Zeiss lens.
Spectra Meter (y) ;)
Not sure why 90% white reflectance is 100% on a waveform? That seem to make no sense to me. And why not use the other side of the card to establish 18% middle grey and check the waveform around 45% to assure accuracy. White should be approx. two stops higher. Not sure how or why that would be 100 on the waveform. The white point set there would have little or no room for highlights that exceed that. Kind of confusing to me.
Yeah, I’ve always just run 41IRE on my 18% grey card for s-log3 then compare to my meter at the same stop/shutter/asa to see if there’s a difference. The FX-6 was bang on.
Yeah, I’ve always just run 41IRE on my 18% grey card for s-log3 then compare to my meter at the same stop/shutter/asa to see if there’s a difference. The FX-6 was bang on.
Thanks for the documents.
Duane Char, you are very welcome!
Is sekonic litemaster pro L-4788D-U a good light meter for a professional cinematographer??
I think most people would opt for the 858 because the spot is tighter and already incorporated into the meter and there is a deeper range of settings overall. If you just need incident readings the 478 would be fine.
@@meetthegaffer what’s your recommendation for a good light meter for a professional cinematographer ??
@@minarimon3106 I own the Sekonic 858 and C800.
Was almost lost when u said asa. Was used to iso.
Ha, ha!
Thanks for this video. I have a question. Can this test be done on film stock as well?
Hello, could you share that google doc that he is referring to please? Thanks!
www.dropbox.com/sh/u144stotjq0o8a5/AABezpKwpDt-FvRdb4n7sHsya?dl=0
@@meetthegaffer Thank you!
This guy speaks the gospel! BORING AS HEL!!! But every single word said is fact.
he is not a stand-up comedian to entertain you
A professional carpenter uses a tape measure. A professional Gaffer should use a light meter.
:)
i don't know who's this guy, but he did not convice me to use a light meter in digital era, when we have waveforms and false colors monitors
the real use of a lightmeter today is when you need a specific ratio between highlights and shadows, because there is no real connection between ire values and stops of light on a logarithmic curve
he failed to demonstrate this, and rendered the video useless
The other use for a light meter is when there is no camera around, but you need to set lights in advance anyway.
@@meetthegaffer nah, that would rarely be the case;
We all have different work flows. Having a meter that is not part of a camera system is a handy tool for lighting, whether setting values with your lamp operators while camera is being set up, keeping looks consistent between sets, re-establishing prior set-up days or weeks later, or just understanding how light falls on a subject from the subjects point of view rather than just the camera’s point of view.
I’m not going to try to convince you to use a tool you find no need for, just know that many experience craftspeople, who also have all the digital tools at their fingertips, find light meters worthwhile. Your mileage may vary.
Sorry, I couldn't get past the constant lip smacking. For God's sake, learn some public speaking skills. Listening to someone smacking his lips constantly is incredibly grating.
Chill, dude. And, learn some social skills.
@@Decadent_Jaguar I'm not the idiot smacking his lips when he talks. THAT is a lack of social skills.