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DSLR as light meter?


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#1 Joshua Green

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Posted 12 August 2009 - 08:43 PM

Hello, I am wondering if I can use my Canon Rebel DSLR camera as a light meter if I set the shutter to 1/24. Would this give me an accurate reading that translates to motion picture film?

In case it's relevant, I am using a Bolex reflex with Canon FD lenses. Thanks.
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#2 Saul Rodgar

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Posted 12 August 2009 - 09:21 PM

If you are shooting at 24 fps you need to set your shutter at 1/48th of a second, not 1/24th. It would be 1/24th only if you had a global shutter, which no film camera has.

http://en.wikipedia....ttent_mechanism

And yes you can get a pretty good idea of what the picture will look (exposure, contrast, etc) if you take digital stills with equivalent shutter and aperture settings to your film camera. I don't know that a digital SLR replaces a light meter, but it certainly helps in most cases. Generally speaking, the whites / highlights tend to blow out faster on digital, while the dark areas will crush to black faster or become too grainy on film.

Edited by Saul Rodgar, 12 August 2009 - 09:25 PM.

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#3 Adrian Sierkowski

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Posted 12 August 2009 - 09:37 PM

Certainly doesn't replace a good light meter (which is cheaper than some DSLRs) but as Saul mentioned you can certainly use them to evaluate exposure if you or the client are worried 'bout the shot. Also make sure to set the ISO to match that of the film you're shooting. Judging how something looks t say F4 1/48th (or 1/50th or 1/60th if you don't have 1/48th) with an ISO of 400 won't do much good if you're shooting ISO (also called ASA or EI) 50 in your bolex
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#4 Ale Reynoso

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Posted 12 August 2009 - 10:15 PM

Hello, I am wondering if I can use my Canon Rebel DSLR camera as a light meter if I set the shutter to 1/24. Would this give me an accurate reading that translates to motion picture film?

In case it's relevant, I am using a Bolex reflex with Canon FD lenses. Thanks.


It´s a common practice to use a DSLR as a reference.
An important aspect is HOW are you going to meter the scene...let the camera "matrix" metering do the work? I would use the spotmeter and start with metering a gray card as a starting point.
May be the DSLR is not such a good reference if you´re looking for the extremes in the highlights and shadows, but a good reference for the overall exposure. The negative could hold detail in highlight or shadows and your camera could be unable to show it (anyway you could set the base exposure and then "aim" to the highlights and/or shadows to spotmeter them. Always from the camera position. Now you can determine how "hot" a highlight is comparing to the base exposure).
Another issue is the sensivity you are really getting in your camera. If the camera is an HS or EBM with the prism system for viewing, you are cutting at least 1/3 of a stop to the film (i.e. if you´re using ISO 500 film you should use ISO 400 in your exposure meter).
You should perform tests to evaluate the correlation between the DSLR sensivity and the effective sensivity you´re getting of the lens+prism+shutter combination (I think the HS shutter is something like 165º).
So light a gray card evenly and USING YOUR DSLR (in spotmeter or covering the entire card, make sure everything is zeroed) meter the card. Using the same sensivity in the DSLR than the label of the can as a starting point. Now roll a couple of feet at "normal" exposure (the f number showed in the DSLR) and over and underexposing in 1/3 of a stop steps up and down to 1 1/2 stops (better to hold the same f number in the film camera and move the lights instead: you´re cutting the iris adjustment error). Make shure you label every gray card (N, + 1/3, + 2/3, etc. or (i.e.) ISO 500, ISO 400, ISO 320, etc.)
Take the roll to the lab and make them tell you wich is the right exposure. Use that in your DSLR.
You should use 1/48s for 24 fps (1/50 in your camera).
It would be a good idea to check the lens too (if the same aperture in the different lens give you the same exposure)...
If it´s not possible just do the maths, substract 1/3 for the prism, and may be 1/3 for the shutter angle (165º is not even a 1/3, but better to overxpose tha sub) to the film ISO to rate the camera. Ideally recheck the DSLR meter with a trusted spotmeter.
Good luck!
Best regards.

Edited by Ale Reynoso, 12 August 2009 - 10:19 PM.

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#5 Jamie Metzger

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Posted 13 August 2009 - 12:23 AM

I've done this before in a pinch, and let me tell you, if you zoom in to the spot you want to meter, it works. Make sure the camera isn't metering the entire image, because then it's going to average it all out for the "best" exposure.

You need the spot meter funcion, and use it to isolate different values to determine the best exposure for your scene.
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#6 boy yniguez

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Posted 28 August 2009 - 06:07 AM

Hello, I am wondering if I can use my Canon Rebel DSLR camera as a light meter if I set the shutter to 1/24. Would this give me an accurate reading that translates to motion picture film?

In case it's relevant, I am using a Bolex reflex with Canon FD lenses. Thanks.



of course you can use a stills camera for metering but do remember that doing so you are reading reflected light not incident so you must take into consideration the difference in metering methods. also the correct shutter speed equivalent is 1/48sec, and also the bolex reflex , if it is the RX model, eats up a third of a stop in its split-prism.

boy
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