Digital camera as night-time exposure meter

[cyrus]

Can any one provide any suggestions on using a Canon XT Digital Rebel as an exposure meter for night-time B&W film photography? I am guessing its just a matter of setting the right ISO to match the film speed (or calculating it) and setting the zoom lens to match the film camera's lens, then taking a test shot - in B&W mode? - then transfering the shutter speed/aperture to the regular film camera, all whilst checking for muggers behind you? (The regular film camera will be my beloved 4x5 polaroid conversion using Ilford HP film.)

I am not a fan of digital cameras - only use them for quickie web shots - but I have come to suspect that my Canon XT's exposure meter is one stop off. I also suspect that the small LCD display won't tell me a whole lot about the quality of the BW test shot.

[Gary Smith]

I am sure somebody is going to have a much better answer than me, but I tried something similar with a Canon 10D a little over a year ago. I found the the results did not match exactly, I mine were off by about 1/2 a stop or so. So if you could calibrate the two, it would work I think. I just was not in the mood to go into that much trouble. There also was a article about this on Luminous Landscape a while back that might be helpful.

I will stick with my spot meter.

Gary

[Brian Ellis]

I've seen tests (maybe in Luminous Landscape) indicating that the Canon dslr film speeds are off by half a stop (i.e. 100 is really 150 etc.). I realize that your camera isn't a dslr but the same or worse may be present with it.

[400d]

As stated in Dpreview.com, the Canon DSLR are acutally 1/3-1/2 stop over. My Minolta Spot Meter F and Canon EOS 1n proves that my 20D is 1/2 stop over.

HOWEVER, 20D seems like a great way to determine exposure under dark scene.
http://i6.tinypic.com/13zwl0k.jpg
My Spot Meter F dies on me (gives me E-Error, since it's under 1EV) for this kind of scene, a blind or educated guess and bracket would be a remedy, but for 4x5? Wow, how many 2-3 mins bracket do you want to do?!

[Bob McCarthy]

How dark will the scene be?

Digital doesn't suffer from reciprocity effect as does film.

You will likely underexpose the film if the time required is in seconds. An adjustment can be made.

Bob

[Chris Strobel]

Brian, I believe his camera IS a dslr :)


I've seen tests (maybe in Luminous Landscape) indicating that the Canon dslr film speeds are off by half a stop (i.e. 100 is really 150 etc.). I realize that your camera isn't a dslr but the same or worse may be present with it.

[markvoce]

I use a Nikon D70 DSLR as a light/exposure meter when using my 5x4.

I simply manually expose the scene with the D70 @ ISO 200, using the the historgram to ensure the correct exposure. I have produced a chart with the exposures already calculated so all I have to do is read off the exposure and I will be given the exposure for Velvia in 1/3 stops.

eg:
--------------------------------
D70@ISO200 | Velvia@ISO100
--------------------------------
F22 @ 25s | F22 1/3 @ 60s
F22 @ 20s | F22 2/3 @ 60s
F22 @ 15s | F22 @ 30s
F22 @ 10s | F22 2/3 @ 30s
-------------------------------

I have been very happy with the results this has given me, its is allways spot on and is very easy to use and calculate.

[dietcookie]

I use a Nikon D70 DSLR as a light/exposure meter when using my 5x4.

I simply manually expose the scene with the D70 @ ISO 200, using the the historgram to ensure the correct exposure. I have produced a chart with the exposures already calculated so all I have to do is read off the exposure and I will be given the exposure for Velvia in 1/3 stops.

eg:
--------------------------------
D70@ISO200 | Velvia@ISO100
--------------------------------
F22 @ 25s | F22 1/3 @ 60s
F22 @ 20s | F22 2/3 @ 60s
F22 @ 15s | F22 @ 30s
F22 @ 10s | F22 2/3 @ 30s
-------------------------------

I have been very happy with the results this has given me, its is allways spot on and is very easy to use and calculate.


I pretty much do this.

http://www.mkaz.com/photo/tools/expcalc.html

That site has helped me alot..Pretty much for T-MAX 100 and E100 VS, 2/3 of my shots have "good" exposure....

[Marko]

Yes, a DSLR can be used to determine correct exposure and it can be a very efficient way to do it.

1. Callibrate your DSLR to the lightmeter you would normally use. Lightmeters built in the DSLRs are all callibrated to match the sensor. Sensors, unlike film, have linear characteristics. Besides, since every unit represents a fixed lightmeter/sensor combination, the numbers do not matter as long as the actual results are correct.

2. Use histogram. Do NOT use LCD for visual evaluation. Histograms are very accurate, LCDs are the equivalent of a web thumbnail.

3. Use reciprocity tables for long exposure - again, the sensor is linear throughout the range.

That's all there is to it.