Fuji FP100-c reciprocity failure table?

Discussion in 'Miscellaneous Equipment' started by Lars Daniel, Jul 17, 2010.

  1. Lars Daniel

    Lars Daniel Member

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    I have searched high and low, but I can´t seem to find any info about FP100-c behaviour in long exposures. I know it is not really meant for long exposures, but I almost took it for granted that there was some useful info floating around somewhere.
    Anyone?
     
  2. E76

    E76 Member

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    Fujifilm provides a reciprocity correction table on page 3 of the film's datasheet.
     
  3. Lars Daniel

    Lars Daniel Member

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    Thanks E76! At least that is good for up to 16 sec.
     
  4. Lee L

    Lee L Member

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    You can derive the Schwarzschild exponent from the information in the .pdf. It works out to a Schwarzschild exponent of about 0.50. Plug that into a formula for correcting only with time instead of f-stops, in which case the correction compounds itself (like interest), and you get the following metered times and corresponding corrected times:


    metered time corrected time
    seconds seconds
    1 3
    1.25 4.06
    1.5 5.25
    2 8
    2.5 11.25
    3 15
    4 24
    5 35
    6 48
    8 80
    10 120
    12 168
    15 255
    18.75 389.06
    22.5 551.25
    30 960

    This is pretty poor reciprocity performance. Most modern black and white films are in the range of .80 to .93, with 1.0 being no reciprocity failure. Most modern color negative and color transparency films would be in the same range as current B&W films.

    Lee
     
  5. Lars Daniel

    Lars Daniel Member

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    Thanks Lee, this is great but now I am also confused:
    The Fuji chart says that a measured time of 4 sec should be corrected one stop which would then be 8 sec, right?
    But your chart says that 4 sec should be corrected to 24 sec. What gives?
     
  6. Lee L

    Lee L Member

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    If you correct by aperture, you can follow the .pdf chart, but if you correct only with exposure time, the adjustment compounds itself just like interest on a bank loan. Consider a Schwarzschild factor of 0.50 a very high rate of interest, with a consequent very heavy compounding effect.

    Lee
     
  7. Lars Daniel

    Lars Daniel Member

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    Thanks Lee. I have some analog theory to check up on :smile: Oh, and your table is just perfect for me. Looking forward to some twilight pola shots!
     
  8. giacoboh

    giacoboh Member

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    It's been a while,
    could you please write the formula you were referring to?

    I found this but my result doesn't match your:

    Relative film speed = d*(t+1)^(p-1)

    [p=Schwarzschild exponent; t=exposure time; declared film speed]


    I'm trying to estimate correct exposure for my pinhole camera (f/315) which use FP-100 with a metered time of about 4 minutes.

    (Sorry for my bad english)
    Thanks,
    Giacomo
     
    Last edited by a moderator: Apr 10, 2012
  9. jp498

    jp498 Member

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    It's not well suited to pinhole, at least without super bright light based on using a box of the stuff myself. It gets a greener cast with longer exposures. A metered time of 4 minutes will go off the scale in guestimated exposure. Some pinhole camera's film holder backs aren't big enough for the pa-45 holder as well. Try it with a normal graflok equipped camera and pinhole lensboard if you need to try before you buy/build a pinhole.
     
  10. giacoboh

    giacoboh Member

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    You're right, all underexposed (despite correct exposure) with that greener cast.
    I'm using a modified Polaroid CU5, nothing special, angle of view is quite ordinary.
    I'll give a last try in bright sun.
     
  11. RalphLambrecht

    RalphLambrecht Subscriber

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    i have something close enough:
     
  12. Lee L

    Lee L Member

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    Your English is far better than my Italian.

    That's the correct formula for adjusting film speed, but use the following to adjust exposure time:

    corrected exposure time in seconds = (t+1)^(1/p)-1

    where t is the metered exposure time in seconds and p is the Schwarzschild exponent. I should probably also state clearly that the metered exposure time in this formula is at the declared film speed 'd', not at the relative film speed from your Schwarzschild formula.

    Lee
     
    Last edited by a moderator: Apr 11, 2012
  13. RalphLambrecht

    RalphLambrecht Subscriber

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    the equation is correct,but how do you know the value for p?
     
  14. RalphLambrecht

    RalphLambrecht Subscriber

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    use this table for tmax100,and note that measured 4 min turn into 40 minutes!
     
  15. Lee L

    Lee L Member

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    Ralph,

    I've answered in a .pdf format to preserve the table.
    Hope this helps.

    Also included a chart for metered times up to 120 seconds, which is of course extrapolating from Fuji's data.
    I believe all the math to be correct, but can't vouch for the accuracy of Fuji's data, and I haven't included the density of the filtration Fuji suggests. As always, test for your own conditions and adjust.

    Lee
     

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    Last edited by a moderator: Apr 12, 2012