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false_Aesthetic
3-Sep-2006, 12:02
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?

Ron Marshall
3-Sep-2006, 12:28
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

Enrico Faini
3-Sep-2006, 13:18
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

Ron Marshall
3-Sep-2006, 13:50
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.

Donald Qualls
3-Sep-2006, 14:11
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...

JW Dewdney
3-Sep-2006, 15:14
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.

false_Aesthetic
3-Sep-2006, 15:14
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

JW Dewdney
3-Sep-2006, 15:16
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

Ron Marshall
3-Sep-2006, 15:32
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

Ron Marshall
3-Sep-2006, 15:33
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

JW Dewdney
3-Sep-2006, 15:40
See the figures at this link:

http://silvergrain.org/Photo-Tech/reciprocity.html


Wow. Thanks - there's a ton of stuff in there. That guy's a maniac. Though I was just looking for something that shows the contraction in curve shape with increased exposure (would assume that the curve gets rather concave...!) - or maybe I should get off my lazy arse and look in one of the books behind me, huh? I have the Zakia/Lorenz book on photographic sensitometry that's been collecting dust for 20 yrs. plus - must be in there...

false_Aesthetic
3-Sep-2006, 18:46
Did fuji stop making b/w film?


All I can find is the quick load stuff on BH's website. Theres no link that I can see on fujifilm.com

Thanks
T

Ron Marshall
3-Sep-2006, 19:18
Did fuji stop making b/w film?


All I can find is the quick load stuff on BH's website. Theres no link that I can see on fujifilm.com

Thanks
T

Here is the b/w:

http://www.fujifilmusa.com/JSP/fuji/epartners/proPhotoProductsNeopan.jsp

Brian Ellis
3-Sep-2006, 22:39
"I think I'm gonna have to find a film with a "better" reciprocity failure curve. . . . Any film suggestions."

According to the reciprocity tables John Sexton hands out in his workshops, TMax films have significantly better reciprocity characteristics than non-tab films such as FP4+.

Leonard Metcalf
4-Sep-2006, 02:49
Fuji Acros 120 - 1000 seconds + 1/2 stop exposure correction

Donald Qualls
4-Sep-2006, 09:07
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.

Generally, it's a given with night photography that your SBR will be completely out of range; in addition, reciprocity failure boosts contrast anyway, because the film exposed to highlights is *faster* than the film exposed to dark areas. There isn't a good way around this; you can apply a contraction, but most methods result in loss of speed as well, which means even more exposure is needed, and you can't apply enough contraction with modern films to make much of a difference (N-2 is about the limit with most of them). In the end, you usually have to accept bright highlights blowing out in order to get an interesting scene, and in fact the blown highlights (mainly actual light sources and lit windows) are part of what makes a night shot look like a night shot.

The best solution has already been proposed -- use a film with better reciprocity characteristics. Fuji Acros is the fastest film you can buy by the time your metered exposure is beyond a couple minutes; at ten minutes, it's faster than TMZ-P3200 (which you can't get in sheet sizes anyway), and it passes Polaroid Type 57 much sooner than that.

BTW, my experience suggests Ilford films, which all fit the 2.81 for 2 curve I posted earlier, are significantly better on reciprocity than Kodak and most other conventional grain films (Foma and Forte, however rebranded, also appear to follow the 3 for 2 curve). Polaroid is much, much worse than that; most Polaroid films just don't work well at all with metered exposures beyond ten seconds (though that's pretty dim conditions with 57/667, it's nowhere near trying to shoot by moonlight).

keithwms
4-Sep-2006, 17:11
http://www.mkaz.com/photo/tools/reciprocity.html

Keith