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Could be a light meter not accurate? (5 replies and 6 comments)

Max A.
3 months ago
Max A. 3 months ago

Hello Mr. Deakins, and all the Dp's over this fantastic forum. I hope the week starts well for you all. As I said some days ago I know that you Mr. Deakins are so busy with the shooting so I don't want to disturb you and I hope this is the right section for this post if it is not I could remove it of course.
I would like to ask for clarification about a light meter.
I bought a Sekonic L478-D some months ago to start using a meter together with the usual external monitor (I have a ninja V not calibrate).
After some exposure and lighting test that I had done with myself (I have white caucasian skin) I've noticed that even if I meter the light with an incident measure with the dome directly toward the light source, my skin appear a bit overexposed, then I thought that it is my skin characteristic and I bought a color and grey chart to test the exposure with the meter.

Now, please correct me if I'm wrong, a light meter (either incident or spot meter) measures the light and gives us an exposure value that serves to expose 18% grey. So If I put a grey chart (that I think is near 18% - brand Datacolor) with a front-lit light and have an incident reading on it, the F-stop that it gives me should be the same if then I use a spot meter directly on the chart. It is correct?
If it is so there is a mismatch between the two results I guess. Now I haven't a spot meter (I've bought one that I could be used with the same incident meter online and waiting for the shipping) but either with False-color tool and Waverform (on Davinci Resolve) the grey card is above the middle point, something like a STOP (I attach pictures below).
Could be possible that the light meter is badly calibrated? Does someone have some experience like this before? Or it is a matter of the color profile of my camera (just a prosumer Canon Eos-R) that gives me back an overexposed image?

I hope this question is pertinent and I want to thank you all for your time.
Sorry if my English is not good enough.

I wish you all a peaceful day.
The Byre
3 months ago
The Byre 3 months ago

There is a wonderful German saying that covers this -

"Wer viel misst, misst Mist."  (He who measures a lot, measures garbage!)  In other words, it is seldom a good idea to over-rely on measurements and better to use your good judgment!  A good on-set monitor might serve you better!

Max A.
3 months ago

I know what you mean and partially agree. We haven't to be slaves of a meter or pure technic but there are moments where being accurate can save our back, mostly for people like me that haven't had decades of experience.
I started with the digital era so I always referred to a monitor but I would like to expand my workflow and be more conscious about the light and ratios to know, then, how to recognize those without (or limiting) the use of tools.

Here in Italy (mostly in the south) there is another saying that cover this (I post directly the translation LOL) " Who do stuff by eye will be never precise".
I think the truth is in the middle, as often Mr. Deakins wrote in this forum it is important to know the technical aspects to let them be our second nature then and don't think about those anymore.

My post is just about a doubt that I have about my meter, I don't know if a meter could be inaccurate (I think it doesn't have to be inaccurate), and ask who has more experience than me if it is something that I have to consider (or have to repair the tool).

Thank you for your answer I like and agree with the concept to rely more and more on my personal judgment and I hope a day to have the best conscious of this.
I wish you a peaceful day.

3 months ago
gabj3 3 months ago

There are definite limitations to tools and cameras surrounding accuracy. Your speed in terms of your meter and camera are dictated by ISO 12232:2006 - the paper in short dictates that x ISO should equal y sensitivity. 

There are a million ways to achieve said sensitivity in a camera and other tool and because of this it isn't uncommon for it to either a) fall-out of 'calibration' or b) just be wrong. 

With this, which one is right? Without a control or a bit of additional information it's impossible to tell. It also doesn't necessarily matter. Unless your camera is grossly uncalibrated and something has gone horribly wrong - in which you'd notice a number of different aberrations such as off-color tints (occasionally in patches) and general unevenness across your image. Calibrate your meter to your camera. 

Thats why you're using it after all!

Note it doesn't need to be exact. The room for error is normally around a quarter to a fifth of a stop.


Max A.
3 months ago

Thank you very much for your answer Gabj. I found a guide to calibrating the meter with a camera (but as you said there are tons of variables that I should add for instance light loss that could be relative to the different lenses, especially if those are not high-end etc.) to have an average idea of what my camera (with that specific color profile) intend for "middle gray" and start from there.

Thank you for your clarification and your time. I wish you a peaceful day.

Roger Deakins
3 months ago
Roger Deakins 3 months ago

I grew up with a meter, no monitor and little latitude in the film I was shooting on. Film, by the way, that was rated at less than a third the speed of an Alexa. Yes, today there is more latitude when shooting with any high end digital camera but, even with the best technicians and equipment, a mistake can be made and calibration can be out. I know I now use a meter less than in the past but I still find it a useful tool, that and my eye. I would caution relying on any technology at the expense of your own judgement.

3 months ago

Wise words indeed. No tool can ever replace the human eye, perhaps imitate but not replace.

Max A.
3 months ago

Thank you very much for your answer Mr. Deakins! As a lot of you have said I will try to rely more on my eye. First of all, I will train (and hopefully learn better) about balancing exposure and multiple light sources with eye judgment so that when I'm starting thinking about an atmosphere then I can try to realize it without being too much crazy on meters or monitors for the exposure balancing.

Thank you again for your answer Mr Deakins. I wish you a peaceful day.
ps. can't wait to see 'EOL'.

3 months ago
dmullenasc 3 months ago

Light meters do need recalibrating now and then but if you figure out that it reads things consistently 1/3-stop over or under, let's say, then it's easy to factor that into account, you could, for example, adjust your ISO setting to correct for that.

You'd have to compare your incident meter reading to a spot meter reading of a grey card, and of course, that's assuming the spot meter is accurate. You could also gather three incident meters and check them among each other to see what the consensus reading is.

The problem with comparing your reading to the monitor image and waveform is that they are measuring a signal with a display LUT applied -- which is fine, it doesn't mean there is something wrong with the LUT, it may be designed to slightly boost the image brightness to better preserve highlights, hence why your meter reading gives you a brighter image, the LUT wants you to underexpose slightly and let it correct the brightness back. So again, if that's true you should just adjust the ISO of your meter to compensate.

Max A.
3 months ago

Thank you for your reply Mr. Mullen
I'm testing these days different things, I calibrated the meter with the camera with the gray chart (with the manufactured software) and seems to be more "accurate" (also if seems still slightly over) but as you said, I also thought that if this thing makes me uncomfortable I can (last chance) try to set my meters 1/3 of STOP over in ISO to "compensate" the difference.
Again, I will test and better train my eye to understand light values and ratios.
Thank you again Mr. Mullen, I wish you a peaceful day.

3 months ago
Rusalen 3 months ago

I don't think it matters that you grew up in the digital age. I also grew up in a digital age with a slight transition. I have been visiting this forum since it had with old interface. I had copied the whole forum then. Then I bought my first Canon 550D I learned a lot from here who had nowhere to know such information about filming. One of the things I remember from here .  You  have to shooting and filming all the time. In this way you will feel for yourself what is right and what is wrong.
I have always relied on the feeling of my eyes, of course, for low-budget films
I also have a Canon Eos-R. For lower class lenses I just add iso. mirrorless camera have no problem adding iso. Until recently, I even worked without a monitor only in camera i mean built-in. I have been using a HD small monitor with an camera form 1 year
аnd I had no problem. . You try too hard to make filming  this exact science ... Just be creative.
There is a third saying that says "if you fall into a hole stop digging".
Of course, it is very important for what purposes you want accuracy.

Sorry for my English.

Max A.
3 months ago

Thank you for the reply Rusalen, practice is the better way I agree. And it is so satisfying (for me) when a theory concept is realized and brought to life with practice doing.
I think the theory is fundamental, and I love to learn more and more, but without practice and experience it remains "empty" and in the last few months, I realized this concept more.
Your English is fine (far better than mine LOL).
Have a nice day.

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