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  1. #1

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    Looooong Exposures on fp4/hp5

    Hi All,

    I am about to start a project with fairly long exposures (several minutes or more) using most fp4+ & hp5+. The chart that Ilford provides is only good out to 35 seconds and the little infomation I found was beyond that Ec=Em^1.48 was the "correct" formula to use. Does this seem right?

    Up until now, I have always used Acros for long exposures, but I want to dry a different look.

    Any insight would be greatly appreciated.

    Thanks!

    Gary
    Build a man a fire and he will be warm for hours.
    Set a man on fire and he will be warm for the rest of his life.

    Sic gorgiamus allos subjectatos nunc.

  2. #2
    Lee L's Avatar
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    This post is a pretty direct answer from Ilford regarding your question about their data. http://www.apug.org/forums/forum37/6...tml#post777356

    You have the correct formula for duplicating the Ilford recommendations, but people who have tested the films find the adjustments using Ilford's information to be significantly overexposed.

    For more information, look for reciprocity failure threads here on APUG, there are a couple running now, and many older ones.

    Howard Bond thoroughly tested 5 films (including HP5+) in 2003 and published this article with charts:
    http://www.phototechmag.com/articles...ciprocity2.pdf

    Patrick Gainer did a follow up on that and a web version of his article is here:
    http://www.unblinkingeye.com/Articles/LIRF/lirf.html
    which gives a quick formula for closely approximating Bond's results.

    For FP4+, using the Gainer formula, try a coefficient of 0.11476.
    That would be: Ec = 0.11476*Em^1.62+Em

    I'm basing this suggestion on data from testing of FP4+ reciprocity loss in astrophotography books. BTW, the books report FP4+ to have the same rate of reciprocity failure as Tri-X, so you could try Bond's Tri-X times for FP4+.

    The Gainer formula coefficient for HP5+ is here on APUG in other threads.

    People who have done much testing of reciprocity also report noticeable variation in the rate of reciprocity failure from one batch to another of the same film.

    Lee
    Last edited by Lee L; 04-02-2009 at 10:00 PM. Click to view previous post history.

  3. #3
    Jim Noel's Avatar
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    Bond's adjustments are much more accurate than those by Ilford. Give them a try.
    [FONT=Comic Sans MS]Films NOT Dead - Just getting fixed![/FONT]

  4. #4

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    You'll get less reciprocity on long exposures on fp4+ or hp5+ by using Fuji Acros. It has very good long exposure response.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  5. #5

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    Also because their reciprocity is so good with really long exposures Fuji Acros or 100Tmax are actually FASTER the HP5+ or Tri-X.

  6. #6

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    Thanks for the help, that was exactly what I was looking for and it provides a good starting point.

    My main film for long exposures until now Acros, (only thing I can get locally), but am just trying for a different look than Acros provides.

    Thanks again.

    Gary
    Build a man a fire and he will be warm for hours.
    Set a man on fire and he will be warm for the rest of his life.

    Sic gorgiamus allos subjectatos nunc.

  7. #7
    jp80874's Avatar
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    Bracket by at least two stops and I always add an extra stop if it is after Thursday. Even if it is Wednesday, it is after a Thursday.

    John Powers

  8. #8
    Jeff Bannow's Avatar
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    Quote Originally Posted by jp80874 View Post
    Bracket by at least two stops and I always add an extra stop if it is after Thursday. Even if it is Wednesday, it is after a Thursday.

    John Powers
    This is the official formula as taught to me by a wise man once ...
    - Jeff (& sometimes Eva, too) - http://www.jeffbannow.com

  9. #9
    Lee L's Avatar
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    The best fit Gainer formula coefficient for HP5+ is 0.12263 according to my regressions against the Bond data using QtiPlot. It's never more than 1/4 stop off from Bond's adjusted numbers, and when it errs, it errs toward more exposure.

    I should probably add (although it shouldn't be necessary) that this difference is as likely to be experimental variation/error in the data as anything else.

    Lee
    Last edited by Lee L; 04-03-2009 at 03:07 PM. Click to view previous post history.

  10. #10
    gainer's Avatar
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    Quote Originally Posted by brianmquinn View Post
    Also because their reciprocity is so good with really long exposures Fuji Acros or 100Tmax are actually FASTER the HP5+ or Tri-X.
    At what point do the curves cross?
    Gadget Gainer

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