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Thread: hp 5 reciprocity

  1. #1

    hp 5 reciprocity

    Does anyone have a reciprocity chart for HP 5? Is it close to Tri-X? Thanks.

  2. #2
    tim atherton's Avatar
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    You'd be amazed how small the demand is for pictures of trees... - Fred Astaire to Audrey Hepburn

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  3. #3

    hp 5 reciprocity

    Scott,

    Some time back David Carper (now sadly ex-Ilford) posted a formula which will approximate the curve that Ilford has determined by testing for reciprocity. The formula is:

    Time (calculated) = Time (measured) ^ 1.48

    where the caret symbol (^) signifies the exponential power

    OR

    Calculated Time = POWER (Measured Time, 1.48)

    An example for an Excel calulation of a measured time of 10 seconds is:

    =POWER(10,1.48)

    = 30.2

    I am also able to perform the same calculation on my palm Pilot using a spread sheet. I just tap in the measured time and another field shows the calculated time. Very handy but unfortunately does not address the issue of altered contrast.

  4. #4
    おせわに なります! Andrew O'Neill's Avatar
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    hp 5 reciprocity

    Hi Scott,

    I did my own testing for HP5+ and reciprocity about 6 years ago and have been relying on it since. I know it's better than the old Tri-X, but not sure about the newer version. Never tried it.
    My data for HP5+ is:

    1 sec = 1/3 stop more exposure

    10 sec = 2/3 (1.5x)

    100 sec = 2 stops (4x)

    256 sec = 3 stops (8x)

    No development compensation is needed.

    You can take the data and make a curve which will give you inbetween times. Time on the bottom and stops on the side. Ilford's compensation curve gives way too much exposure compensation. At least that's what I observed.

  5. #5

    hp 5 reciprocity

    Hey Guys,

    Thanks so much for getting back to me so quickly! Great information. Now I can go back to work with confidence. It looks like the curve for HP 5 is different than the one I've been using for Tri-X, so I'm glad I asked.

  6. #6
    Dave Karp
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    hp 5 reciprocity

    Scott,

    Steve Simmons gives a chart with his findings for Ilford films' reciprocity characteristics. I have tried and find that it is right on target for my work. It is found in his book "Using the View Camera."

  7. #7

    hp 5 reciprocity

    Does anyone have a similar formula for other Ilford mono films?

  8. #8
    Dave Karp
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    hp 5 reciprocity

    I believe that Simmons' book lumps all Ilford films together. I think that Ilford gives the same information for adjusting exposure due to reciprocity for all their films as well.

  9. #9

    hp 5 reciprocity

    Sorry, I was talking about the Carper formula (above) rather than the Simmonds book -- although does Simmonds say that all Ilford films have the same characteristics? If so then the formula would be the same.

  10. #10
    Dave Karp
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    hp 5 reciprocity

    Mark,

    If I recall correctly, David Carper's formula applied to all Ilford b&w films, not just HP5+.

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