fp4+ reciprocity failure (and a short question about pre exposure)
Hey,
Ilford's reciprocity failure chart for fp4+ stops at 30 seconds. My exposures are running around 15 min rating fp4+ at 100.
When I shoot color (Fuji NPS 160) I rate the film at 100 and double the exposure time--my negs are awesome.
Thinking that I wasn't compensating enough, I rated FP4+ at 80 and then doubled the time.
I'm still getting thin negs. Suggestions? Anyone have an extended reciprocity failure chart fo rfp4+?
Thanks
T
p.s. I'm about to do a test with pre exposure to try and fill in the shadows. Ansel says zone 2. I'm starting at Z 1. My thought is that if I pre expose too much then I'll have an effect that looks kind've like fogged film. Since I'm shooting at night and there's a lot of area hanging around Z 2, I don't want to pre-expose around Z 2 because it'll look fake. Am I thinking correctly?
Re: fp4+ reciprocity failure (and a short question about pre exposure)
Have a look at figure 7 on the following link. The curve for FP4 should be similar to that for PlusX. Since it approximates a straight line you can extrapolate to get a starting exposore to be refined by testing. Fifteen minutes is 900 seconds, lets say 1000 or 10 to the power of three for ease of computation. The correction is about 1.17 stops per power of ten, from the slope of the line. So for a 15 minute (metered) exposure you will need to increase the exposure by approximately 4.67 stops, or 25 times as long, ie. a 6 hour exposure. You will need a compensating developer to keep the highlights from blocking-up.
Have a look at the curve for Acros. With Acros you would need only a 24 minute exposure.
http://silvergrain.org/Photo-Tech/reciprocity.html
Re: fp4+ reciprocity failure (and a short question about pre exposure)
with FP4+ for exposures longer than one second I calculate the exposure time by taking the metered time and raising it to the power of 1.48.
then depending on the scene's contrast and the resulting exposure time I guesstimate how much I should reduce the development
works fine, but I have never tested it for exposures longer than a few minutes
Re: fp4+ reciprocity failure (and a short question about pre exposure)
Quote:
Originally Posted by Enrico Faini
with FP4+ for exposures longer than one second I calculate the exposure time by taking the metered time and raising it to the power of 1.48.
then depending on the scene's contrast and the resulting exposure time I guesstimate how much I should reduce the development
works fine, but I have never tested it for exposures longer than a few minutes
Interesting, the time I calculated using your method is very close to what I extrapolated from the curve: 6.5 hours.
Re: fp4+ reciprocity failure (and a short question about pre exposure)
That's also close to what I'd get using my (empirically derived from the Ilford chart) factor of 2.81x for each stop past one second instead of 2x -- I take the metered exposure in seconds (15 minutes would be 900), calculate the logarithm base 2 (Log-X key, then divide by log of 2), and raise the result to the power of 2.81 (for Plus-X and Tri-X, and most other conventional grain films, I use power of 3 instead). So,
log2(900)^2.81 = 7 hours and a fraction of a minute.
Hope you have a sturdy tripod and no curious kids in the neighborhood at night...
Re: fp4+ reciprocity failure (and a short question about pre exposure)
Quote:
Originally Posted by Donald Qualls
That's also close to what I'd get using my (empirically derived from the Ilford chart) factor of 2.81x for each stop past one second instead of 2x -- I take the metered exposure in seconds (15 minutes would be 900), calculate the logarithm base 2 (Log-X key, then divide by log of 2), and raise the result to the power of 2.81 (for Plus-X and Tri-X, and most other conventional grain films, I use power of 3 instead). So,
log2(900)^2.81 = 7 hours and a fraction of a minute.
Hope you have a sturdy tripod and no curious kids in the neighborhood at night...
Wow. I've always been very 'shoot from the hip' about reciprocity failure compensation - I would normally translate 15min. into about 2.5 hrs! I wonder what sort of SBR Ilford are taking into account. Normally, you'd think film manufacturers are taking a best-case scenario - but here it sounds a bit more worst-case, and I'd worry a bit about highlights in high-SBR scenes. I think there are some situations where losing your low-level shadow detail isn't so important in the big picture.
Re: fp4+ reciprocity failure (and a short question about pre exposure)
I think I'm gonna have to find a film with a "better" reciprocity failure curve.
Everything was so much easier when I shot color. . . I'm desperately trying to stay away from shooting in color and throwing out the color in Photoshop.
We'll see if pre-exposure helps.
Any film suggestions?
(**grumble** I wish I had more technical instruction for b/w than incident meter + d-76 1:1 + tri-x = good print)
Thanks so much guys,
T
Re: fp4+ reciprocity failure (and a short question about pre exposure)
Out of curiosity, has anyone ever published a set of curves (log D vs. exposure) that are accessible online - showing what happens with increased exposure time
Re: fp4+ reciprocity failure (and a short question about pre exposure)
Quote:
Originally Posted by false_Aesthetic
I think I'm gonna have to find a film with a "better" reciprocity failure curve.
Everything was so much easier when I shot color. . . I'm desperately trying to stay away from shooting in color and throwing out the color in Photoshop.
We'll see if pre-exposure helps.
Any film suggestions?
T
Acros has the best reciprocity characteristics
Re: fp4+ reciprocity failure (and a short question about pre exposure)
Quote:
Originally Posted by JW Dewdney
Out of curiosity, has anyone ever published a set of curves (log D vs. exposure) that are accessible online - showing what happens with increased exposure time
See the figures at this link:
http://silvergrain.org/Photo-Tech/reciprocity.html