f-stops, shutter speed, ISO, light meter and testing with a DSLR

[Ray Drueke]

Hi,
I'm not sure this is the correct section for this question but I'll ask anyway. If it needs to be moved, please do so.

I'm just starting with large format having built a 4x5 last December and just finishing refurbishing a 9A Century Studio 8x10. I've acquired a couple meniscus lenses and Packard shutters and want to use them on an upcoming shoot. I'll be using ISO400 B&W film so I want to use my DSLR for test shots to ensure the (reasonably) correct f-stop etc. I'll be using the instantaneous exposure mode of the Packard so I'm at 1/25th for shutter speed. I plan to use ND filters to get the f-stop I'd like for soft focus. This will also be my 1st time with ND filters.

If I really understand everything fairly well I should be able to use manual mode on the DSLR, set the same f-stop and shutter speed and ISO and use the same ND filter and get the same result when looking at the chimp screen, Right???

Ie, is f2.8 the same % opening on a 105mm lens in DSLR (full frame) and my 285mm meniscus lens on the 4x5?
I know its not same area.

If my theory isn't correct how can I do some test shots to get the correct f-stops and ND filter? I'd really not have to use film for test shots since the scene will be set up the day of the shoot.

Thanks,
Ray.

[vinny]

light meter.
your slr will get you close but won't help with bellows ext factor. that's assuming you've tested the film you're using for the proper iso.

[Frank Petronio]

F/2.8 or f/5.6 is universal, if the lens is marked then you can use it at the same aperture value as your modern plastic DSLR lens. Of course if it is heavily fogged/hazed up you will loose some light transmission but if the lens looks relatively bright and clean when you look through it opened up, then I wouldn't worry about.

A light meter won't calculate bellows factor either, nor will it compensate for ND filters. Not saying that it wouldn't be best to use one, but a DSLR and some simple mental arithmetic will get you the same result and you'll run the same risk of forgetting! Better to judge the exposure via the histogram and make the shutter speed/ISO/aperture consistent between cameras. Then add the recommended ND and bellows factor compensations.

[Ivan J. Eberle]

Welcome, Ray. For some this is real hot-button topic. Traditionalists will jump in to excoriate DSLR metering, usually the argument is that you don't know what you're getting with the histogram, yadayadayada. But a DSLR may indeed be more accurate than any handheld meter. My RGB metering Nikons have color temperature agnostic spot metering, arguably better than any CdS or Selenium cell meter. Biggest drawbacks to using a DSLR are bulk and weight. Minor issues are that most lenses won't stop down past f/22 and ISO's don't typically go lower than 100.

As Frank indicates, it's all just a mental gymnastics exercise after you have a reading. You will also want to bone up on bellows and filter factors, but since you're using B+W neg film it's not going to be super critical. Your shutter may not time exactly on the money anyway. Err on the side of over-exposure, not-underexposure.

[Oren Grad]

ISO calibration of digital cameras is different from ISO calibration of film. Doesn't mean you can't use a DSLR meter, but if you want to be sure of what you're going to get you should do a set of test exposures in advance of the event to see how the film comes out at various settings, or at least find a friend with an old-fashioned hand-held meter or film camera with meter and compare against that. Also, best to use the spot or centerweighted meter pattern in your DSLR, since multisegment/matrix metering adds in the wild card of the manufacturer's secret pattern-based fudge factors.

In any case, don't lose too much sleep - in general, ISO 400 B&W negative films have very substantial exposure latitude.

[John Kasaian]

I vote sunny 16

[SergeiR]

ISO calibration on both (film and dSLR) might go around within 1 stop on dSLR and a bit on film. So it could be a tad different. You will need to adjust settings on dslr a bit to lower contrast too. Bellows factor won't be calculated and DOF will be different. Other than that its doable. Many use digital as polaroid proofs

[Ray Drueke]

Hi,
Thanks for the tips - I think it will work out well. I hadn't thought about bellows factor but the meniscus lens I want to use has Waterhouse stops with the equivalent f stop printed on each stop for 10' and 40" focus distances (thanks to Reinhold Schable). At worst I think the bellows factor is about 1/3 to 1/2 stop at 10'. I'm shooting Kodak ISO 400 B&W negative film so I will have about a stop of leeway.

I can also mount the ND filters (Cokin type filters) on the DSLR (Nikon D700) and use spot metering. I have a Sekonic L-358 that seems to match up pretty well with the Nikon and an old Minolta X370 I bought new many years ago.
To err on the side of over-exposure maybe I can round up to the next larger f stop.

Thanks again,
Ray.

[E. von Hoegh]

You can get a LunaPro for $50 or less. You can use hearing aid cells and meter a black cat in a coalmine at the new moon on a cloudy night. I think there's a LunaLux in the FS section for $60, this takes a standard 9 volt battery and is an excellent meter. You'll need a real meter soon enough.

[retnull]

Instead of carrying a DSLR or a light meter, you could use the iPhone app "Light Meter". It's good, and free. Don't know if there's a similar app for Android phones.