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Thread: fp4+ reciprocity failure (and a short question about pre exposure)

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    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?

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    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

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    Enrico Faini's Avatar
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    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

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    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.

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    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...
    Last edited by Donald Qualls; 3-Sep-2006 at 14:12.
    If a contact print at arm's length is too small to see, you need a bigger camera. :D

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    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.

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    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

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    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

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    Re: fp4+ reciprocity failure (and a short question about pre exposure)

    Quote Originally Posted by Ron Marshall

    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...

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    Re: fp4+ reciprocity failure (and a short question about pre exposure)

    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

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