Contrast and Reciprocity Failure

[Vlad Soare]

Hi, guys,

I posted this on Photo.net, too. I apologize to those of you who might read it twice.

I recently took a picture of a church interior. The shadows (which I wanted to place in Zone III) and highlights were four stops apart. So far, so good. But in order to place the shadows in Zone III, I needed an exposure of 1 minute, which due to reciprocity correction became 12 minutes.
Lengthening the exposure to compensate for reciprocity failure also raises the contrast. I should probably pull the development, but by how much? Is there a formula? At least an approximate one? Should I try N-1? Or N-2?
Unfortunately, due to the long exposure time and the fact that I had already pushed my luck by mounting the tripod in a church, I couldn't take a backup exposure. I only have one sheet, so I only get one chance to develop it right.
Should I err on the side of underdeveloping, relying on the fact that adding contrast during printing will be easier than subtracting it? I'm aiming for wet darkroom printing.
The film in question is Fomapan 100.

Thank you.

[Vaughn]

Tri-X needs only about 9 minutes for a 1 minute exposure, Tri-X exposed for 9 minutes to compinsate for a metered 1 minute exposure should be developed about 30% less (according to Kodak's tech sheet on the new version of Tri-X). Might give you a starting point.

You could easily duplicate the lighting in your living room, take a couple shots and do your tests on them.

Vaughn

PS

http://www.foma.cz/Upload/foma/prilohy/F_pan_100_en.pdf

Interestingly, the tech sheet for Fomapan gives a recommended increase of exposure for long exposure times...but gives no recommendation for reducing the development. So I repeat my recommendation of duplicating the lighting in your living room and doing a couple tests.

[Doremus Scudder]

Vlad,

It very much depends on which film you are using, as Vaughn indicated above.

That said, I routinely use a "rule of thumb" that reduces development time by 10% for each doubling of the exposure time. However, it depends heavily on arriving at the correct exposure compensation for your film It seems to me that you have over-compensated for the reciprocity failure. I know of no film that takes so much compensation for a one-minute exposure.

For example, Tri-X is about 9 minutes (the new version slightly less)

Bergger BPF 200 (and the other labels it it marketed under) is only 4 minutes

T-Max films are even less.

The overexposure is probably not a problem, but you don't want to develop too little (you lose a lot of film speed too with reduced development in addition to the contrast recuction).

I would recommend re-checking the reciprocity-failure data for the film you used. You will probably find you overexposed. Don't worry about the overexposure, simply take what should have been the proper exposure time and apply the rule above to arrive at a figure for reducing your development. For example:

IF your film data calls for an 8-minute exposure...


1*2 = 4 (one doubling, - 10%)
2*2 = 4 (two doublings, - 10%)
4*2 = 8 (three doublings, - 10%)

Total development reduction = minus 30 % (what Vaughn recommended)

You should, of course, base your actual development reduction on the published exposure compensation data for the film you were using (NOT on your actual exposure).


Hope this helps some,

Best

Doremus Scudder

[Vlad Soare]

Doremus, Fomapan is one of the worst films when it comes to reciprocity failure. I personally don't mind that, firstly because I love it for other reasons, and secondly because in this particular case the long exposure was advantageous to me (people could wander in front of the camera without being recorded).
The reciprocity correction for Fomapan 100, according to its official data sheet, goes as follows:
1s - 2x
10s - 8x
100s - 16x
My inference was that 60s is halfway between 10s and 100s, so the compensation must be (at least approximately) halfway between 8x and 16x. Thus 1 minute became 12 minutes. Well, I know it's not a linear function, but the error cannot be that great.
Unfortunately, as Vaughn noticed, the Foma data sheet gives no indication regarding any development correction.

Trying to duplicate the lighting at home and to make some tests seems like a great idea. I think I'll try that.

Thanks.

[Nathan Potter]

Vaughn is spot on. If you have your metering data from the single photo, rig up reflection objects in your home area and duplicate the metering of the original scene. Take several photos and try N, N-1 and N-2 development tests. I've done this with both interior and exterior scenes where I've realized that I've mis-exposed, especially if the image is particularly valuable.

Nate Potter, Austin TX.

[Brian Ellis]

Going from 1 minute to twelve minutes is a gigantic reciprocity correction, I've never heard of anything even close to that kind of a correction when the metered exposure is only a minute. For comparison, with T Max a metered 1 minute exposure becomes 2 1/2 minutes, with all other films (except Fomopan apparently) a 1 minute metered exposure normally becomes 5 minutes. With T Max the contrast increase is N+1 at 2 1/2 minutes, with all other films it normally is N+2. So if I wanted normal contrast with a film other than T Max I'd process for N - 2. I don't know if that holds for Fomopan since it apparently is a very different film than all others when it comes to reciprocity failure but that's what I'd try.

[CG]

The various contradictory sites I've checked out say Tri-X at a metered minute expands to anywhere between 4 minutes and 9 1/2 minutes.

C

[Vaughn]

The various contradictory sites I've checked out say Tri-X at a metered minute expands to anywhere between 4 minutes and 9 1/2 minutes.

C

Off the Kodak website I found their tech publication for Tri-X...the graph says for 60 second exposure, increase to 550 seconds (9.2 minutes).

Like anything else, one's mileage may differ.

Vaughn

[Bruce Watson]

Tough situation. Just remember that reciprocity failure typically only happens in the shadow areas -- not enough photons hitting the film to form a stable latent image. The highlights however, are doing fine with plenty of photos and normal latent image formation. Then when you increase exposure to handle the reciprocity failure in the shadows you way overexpose the highlight areas. In your case, you literally cook them with 10x the exposure they should get. It shouldn't be any wonder then that your highlights might be very dense indeed.

For this piece of film I would probably give it N-2 or N-3 processing. And hope that Foma shoulders strongly. But I would also expect that it will be very difficult to print in the darkroom because of the highlight density.

In the future I suggest that you use a neutral density filter. Sounds crazy doesn't it? But what I think you should do is reduce the light hitting the film until the entire sheet is in reciprocity failure, shadows to highlights. Your exposure will be measured in hours. But your film should have a much nicer density range and should be easier to print.

Since every film will respond differently to such treatment you'll have to experiment a bit to find out what really works best for you. But at least I've given you something to think about maybe.

[Nathan Potter]

Bruce, that's an interesting approach - using a neutral density filter to effect uniform reciprocity failure everywhere. Never thought about that. But if this failure is highly nonlinear as a function of incoming photon density - I think it's an avalanche multiplication effect failure that yields the nonlinearity - are you sure that the application of a neutral density filter which will not change the brightness range of the scene - only reduce it - would help. I'm writing this without thinking it through clearly. I need to get my French Press going!

Nate Potter, Austin TX.