Using a digital camera as a light meter to shoot film

[Alan Edward Klein]

Ok Alan, allow me to be polite. It is a very short article issued by the same people who write the ISO standards. To add to what @wiltw already said I quote from the main document (ISO 12232):

"This document was designed to harmonize with earlier standards developed for film-based photography. For example, the equations were chosen so that using a particular EI on a DSC should
result in approximately the same camera exposure settings, and resulting focal plane exposures, as would be obtained using the same EI on a photographic film camera. For example, the value of 10 as ISO 12232:2019 the constant in Formula (1) of this document is consistent with ISO 2721, so as to harmonize with this earlier ISO standard for photographic film cameras. ISO 2721 uses the term nominal exposure and assumes that the nominal exposure is an arithmetic mean exposure value, which usually corresponds to the mid-tone in photographs of average scenes."

I appreciate your clarification and saving me time. So meters in digital cameras, film cameras, and handheld meters all measure the same value for the same input and regulate the same as far as exposure is concerned.. Thanks. That makes sense.

 

[DMJ]

So meters in digital cameras, film cameras, and handheld meters all measure the same value for the same input and regulate the same as far as exposure is concerned..

Yes...but there is the calibration constant (as someone mentioned above). The K constant is the reflected-light meter calibration constant and the C constant is used in incident meters. Constants are multipliers. For example Sekonic, Canon, Nikon use a calibration constant of 250 to calculate EV given Lux and ISO with a flat receptor. A constant of 330 is used with a hemispherical receptor (diffuser).

The constant value can be found in the manuals of some light meters.

 

[MattKing]

It's the only way to get exposure readings and settings to follow industry standards. Otherwise, the photographer would not be able to make filter adjustments or use handheld meters. Who would buy a camera like that?

But you aren't trying to do that Alan.
You are trying to use the in-camera readout (not the meter reading itself) from your digital camera in an entirely unconnected piece of equipment.
That in camera readout isn't there for that purpose - it is there to inform you, but not to assist you in setting anything on another camera.
As I said, if you check it, over a wide range of circumstances, and it matches the results of a piece of equipment that is designed to be used with other cameras, then go ahead and use it for that purpose.

 

[Alan Edward Klein]

But you aren't trying to do that Alan.
You are trying to use the in-camera readout (not the meter reading itself) from your digital camera in an entirely unconnected piece of equipment.
That in camera readout isn't there for that purpose - it is there to inform you, but not to assist you in setting anything on another camera.
As I said, if you check it, over a wide range of circumstances, and it matches the results of a piece of equipment that is designed to be used with other cameras, then go ahead and use it for that purpose.

That was my original question. Let's just assume for the moment all the meter readings are the same and there are no variables.

1. First, can we assume that the exposure reading in the camera is the proper reading for the film cameras as it's reading middle gray as if we read it with a hand held meter? (Assume we're reading the right subject, let's say a gray card.) So we can set the film camera for the same setting. So far so good?

2. The question is if a subject scene's histogram in the digital camera shows clipping the white at the same middle gray setting when we take away the gray card and read the actual scene, does that correlate in a way I can adjust the setting for the film shot? Because the DR of the cameras is different then film, how would I if possible take that into consideration? I think if there was no clipping in the histogram, we can assume the shouldn't be clipping in the film shot because the DR is smaller in film? (Is that correct?

 

[Sirius Glass]

Take the digital camera’s reading for the box speed ISO and add 1/2 f stop. OR as a friend I recommend that you just a good light meter.

 

[Alan Edward Klein]

Take the digital camera’s reading for the box speed ISO and add 1/2 f stop. OR as a friend I recommend that you just a good light meter.

That's what I do for BW film. I subtract a half stop for chromes.

 

[moggi1964]

I just got the Doomo S for my film cameras. Love it.

I did use my digital camera for a while then I used a phone app. Doomo S is so much easier.

Not as good as a Sekonic meter, not as versatile but I'll make it work.

 

[BradS]

Well, let's say the camera has a dynamic range of 10.2 stops as my digital camera that I use as a light meter has. However, Velvia 50 chrome has about 4 maybe 5 stops of dynamic range. So it's easy to clip film. So now I check a scene and the meter in the digital camera shows white are clipping. However, since film is different. that doesn't necessarily mean that the film will clip, or does it?

I;m trying to correlate the clipping shown on the digital camera meter to determine if I;m clipping with the film at the same exposure setting. Does the correlation hold true to both or do I have to make an offset to the exposure with the film camera?

Don't let the fact that the digital camera meters the whole scene at once and displays the result in such a wonderfully clear concise and information packed manner fool you.
This is always an issue regardless of what meter is being used to determine camera settings. It is often the case that the exposure latitude of the film in use is smaller than the range of scene brightness. If one is being careful, then multiple measurements must be made. Again, the only difference is that the digital camera does the measurements all at once and displays the result in a histogram. Does that make sense?

Incidentally, we have the same problem again when we try to print a black and white negative in the dark room. The film may have 10 stops of density but the paper can really only represent 5~8 stops or so.

....I hope that's clear.

Usage of the word "clipping" may be leading to some confusion. The exposure-density response curve of film is usually (always?) a smooth, differentiable, continuous curve but clipping, at least in my mind, is characterized by a discontinuity or non-smooth, non-differentiable change in the response...so, clipping may not be quite the right word to use when talking about the response of film. Film doesn't clip, the slope of the response may change and be nearly flat but it is still a smooth differentiable function.

 

[BrianShaw]

I appreciate your clarification and saving me time. So meters in digital cameras, film cameras, and handheld meters all measure the same value for the same input and regulate the same as far as exposure is concerned.. Thanks. That makes sense.

Not necessarily. Only if they conform to the standard. And only if they use the same constants, although those differences might be insignificant from a practical perspective.

 

[cowanw]

1. First, can we assume that the exposure reading in the camera is the proper reading for the film cameras as it's reading middle gray as if we read it with a hand held meter? (Assume we're reading the right subject, let's say a gray card.) So we can set the film camera for the same setting. So far so good?

The difficulty with the ISO statement in post 52 is that they are designed (film and digital exposure measurements) for two completely different endpoints. The film ISO standard is designed to reproduce a response to light based on the film as a negative output (specifically not a positive). The digital ISO measurements are designed to produce similar (actually reversed but equivalent looking as an output) shades of light and dark when used with the proprietary companies algorithms to produce a positive image on a computer screen.
So, Alan,. your statement #1 in post 56 is only true if you use the correct associated algorithm and output.
No matter how much you want them to be the same and regardless of whether they work most of the time, they are not the same thing.

 

[Sirius Glass]

One very important thing to remember is to never forget include the sky in the camera or meter reading. Measure the light of the subject without the sky and use that reading (with or without adjustments) and the sky exposure will work out on its own.

 

[Alan Edward Klein]

Not necessarily. Only if they conform to the standard. And only if they use the same constants, although those differences might be insignificant from a practical perspective.

I'm assuming that they would be essentially the same because I got the same readings using a gray card. The question is how to interpret the histogram against film?

 

[Alan Edward Klein]

Don't let the fact that the digital camera meters the whole scene at once and displays the result in such a wonderfully clear concise and information packed manner fool you.
This is always an issue regardless of what meter is being used to determine camera settings. It is often the case that the exposure latitude of the film in use is smaller than the range of scene brightness. If one is being careful, then multiple measurements must be made. Again, the only difference is that the digital camera does the measurements all at once and displays the result in a histogram. Does that make sense?

Incidentally, we have the same problem again when we try to print a black and white negative in the dark room. The film may have 10 stops of density but the paper can really only represent 5~8 stops or so.




Usage of the word "clipping" may be leading to some confusion. The exposure-density response curve of film is usually (always?) a smooth, differentiable, continuous curve but clipping, at least in my mind, is characterized by a discontinuity or non-smooth, non-differentiable change in the response...so, clipping may not be quite the right word to use when talking about the response of film. Film doesn't clip, the slope of the response may change and be nearly flat but it is still a smooth differentiable function.

Yes, that makes sense. I'm assuming if there is no clipping at either end of the histogram, then I:m safe to capture the whole response of the picture on my film camera if I set the settings as is on my digital camera. Basically, that's what people o when using a handheld meter using center average or an incident reading.

The question is how to handle histograms where either end is clipping. I realize film doesn't;t clip. But what caution should I take that I'm not pushing the film into undesirable ends? I mentioned a 1/2 stop less exposure if that occurs on the high end and a half more exposure if it occurs on the dark end. Does that make sense?

Assuming no clipping, would you still add a 1/2 stop on negative or subject a 1/2 stop for chromes?

 

[Alan Edward Klein]

The difficulty with the ISO statement in post 52 is that they are designed (film and digital exposure measurements) for two completely different endpoints. The film ISO standard is designed to reproduce a response to light based on the film as a negative output (specifically not a positive). The digital ISO measurements are designed to produce similar (actually reversed but equivalent looking as an output) shades of light and dark when used with the proprietary companies algorithms to produce a positive image on a computer screen.
So, Alan,. your statement #1 in post 56 is only true if you use the correct associated algorithm and output.
No matter how much you want them to be the same and regardless of whether they work most of the time, they are not the same thing.

I'm sorry. But I don't understand. Could you clarify?

 

[Alan Edward Klein]

One very important thing to remember is to never forget include the sky in the camera or meter reading. Measure the light of the subject without the sky and use that reading (with or without adjustments) and the sky exposure will work out on its own.

I assume you;r referring to BW negative film? If the entire scene can be captured without clipping, I use an average reading than add a half stop.

 

[BradS]

@Alan Edward Klein Please forgive me if I say something dumb. I'm not at all familiar with digital cameras. It may very well be the case that my understanding, mental model of what the digital camera is doing is incorrect.

Is this a situation where the actual scene brightness range is wider than the ten stops (or whatever) that the camera's histogram displays?

...but this is precisely where one meters some shadow area (for example) and places that in a particular zone - realizing and accepting that some highlights may be blown or that there will be some loss of detail in some depth of shadow.

So, I'm afraid this does not address your specific question but maybe it points to a sort of pit fall associated with the method considered. The histogram present the user with excess information. The user must still decide what compromise to make...that's the artists decision.

 

[wiltw]

I'm assuming that they would be essentially the same because I got the same readings using a gray card. The question is how to interpret the histogram against film?

Alan, you are making things UNNECESSARILY complcated!
Consider this...

The nominal exposure which renders 18% at its inherent brightness is not different for color neg vs. for color transparency...the CENTER of exposure places the midtone density on the film...yet color heg has wider DR than color transparency means that 'highlight with no detail' occurs closer to the midtone value (e.g. +2.5EV) with color transparency than 'highlight with no detail' occurs with color neg (e.g. +3.5EV) -- I am not claiming those are actual limits...merely stated for illustrative purposes!
For analogy, substitute 'digital exposure' for 'color neg' in the preceding statement, and you see simply that the deviation from the center tone is a higher DR for digital than it is for color transparency. Similarly, the range of DR is greater at ISO 100 exposure than it is for ISO 12800 exposure...the DR shrinks (gets less broad) with higher ISO value. But the CENTER of the exposrue is the same for all!​

 

[BradS]

.....
The question is how to handle histograms where either end is clipping. I realize film doesn't;t clip. But what caution should I take that I'm not pushing the film into undesirable ends? I mentioned a 1/2 stop less exposure if that occurs on the high end and a half more exposure if it occurs on the dark end. Does that make sense?

Assuming no clipping, would you still add a 1/2 stop on negative or subject a 1/2 stop for chromes?

I re-read your post and will try again.
If the histogram is clipped at one end only then, perhaps changing the camera setting on the digital camera will move the histogram so that it does not clip ?

However if the histogram runs off the ends on both ends then...as I said above. We choose something in the scene that is important and place it in a certain zone - accepting that at some extreme end, the tones will not be distinct. You cannot fit twenty pounds of stuff into a five pound sack. You have to choose which part to fit into the range that the film "sees".

 

[RalphLambrecht]

I started using my digital camera as a light meter. Here's what I do.

I adjust the manual settings so the histogram on the camera is in range so it's not clipping at either end. I check the LED viewfinder to see if it looks right. Then for BW film, I raise the exposure by about 1/2 stop to pick up more shadow details as long as I'm not clipping the highlights.

With color chromes, I do the opposite lowering the exposure so I don't clip the highlights.

Of course, if the range is way beyond the histogram like you get with sunny skies, I might need a graduated ND filter to keep everything in range.

One issue I see in my method is that the digital camera's range of stops is greater than my film. So where it clips would be incorrectly shown on the histogram. But I'm figuring that's really no different than a handheld meter using reflective readings. So as long as the "average" reading is in the middle, a little 1/2 stop adjustment should work.

Does anyone have any comments on this process or ideas to get better exposure readings?

Seems like a valid and logical approach to me especially if that works for you.

 

[Alan Edward Klein]

@Alan Edward Klein Please forgive me if I say something dumb. I'm not at all familiar with digital cameras. It may very well be the case that my understanding, mental model of what the digital camera is doing is incorrect.

Is this a situation where the actual scene brightness range is wider than the ten stops (or whatever) that the camera's histogram displays?

...but this is precisely where one meters some shadow area (for example) and places that in a particular zone - realizing and accepting that some highlights may be blown or that there will be some loss of detail in some depth of shadow.

So, I'm afraid this does not address your specific question but maybe it points to a sort of pit fall associated with the method considered. The histogram present the user with excess information. The user must still decide what compromise to make...that's the artists decision.

Thanks for you input. I could use spot metering with the digital camera and switch to the zone system or minimally set zone 3 as you did. That's an option but not what I'm trying to ascertain using overall exposure metering. But thanks for the idea.

 

[Sirius Glass]

I'm sorry. But I don't understand. Could you clarify?

I assume you;r referring to BW negative film? If the entire scene can be captured without clipping, I use an average reading than add a half stop.

All photographs: Color slides, color prints, and Black & White. With that alone you will get better shadow detail. Do not make things hard.

 

[Alan Edward Klein]

All photographs: Color slides, color prints, and Black & White. With that alone you will get better shadow detail. Do not make things hard.

I wouldn't add a 1/2 stop with chromes. It could overexpose whites.

 

[Sirius Glass]

I wouldn't add a 1/2 stop with chromes. It could overexpose whites.

With a number of different light meters and cameras with light meters I just used the light reading and took the slides. No games. No fuss. It works. Again why are you making things so hard?

 

[Chan Tran]

Well hand meters work the same way. You get a different reading depending on where you point it or the angle it's reading. Metering is actually easy. Once you know where to point it.

None of the hand held meter I know has Matrix or Evaluative mode. They have spot (with various spot size, most often is 1 degree), wide angle reflective (typically 40 degrees), Incident with both spherical and flat diffuser. The Matrix and Evaluative metering system works quite different from the other types although it's a reflective type.

 

[Chan Tran]

What does that mean? I don't know what those constants are.

K is for reflective and C is for incident meter. If you don't know oh well.