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Thread: Bergger Pancro 400 Reciprocity Characteristics

  1. #1

    Thumbs up Bergger Pancro 400 Reciprocity Characteristics

    I like Bergger Pancro 400 in 4x5 and became curious about how it behaved with long exposures. Now that it is available in 135, I am able to expeditiously and affordably experiment.

    Knowing that most films follow an exponential curve, I set up a target in dim light and shot a few rolls of 135 at various exposure times to determine the "right" exposure. I tested this method on FP4+ (for which Ilford has published power law reciprocity characteristics, thanks Ilford!) beforehand.

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    I controlled exposure of the target using a tungsten fresnel lamp and CTB+ND gels. The "meter" I used for this was a Canon 5d Mark III (which is my typical long exposure meter). I first determined that the digital camera exhibits "correct" reciprocity across shutter/aperture/ISO settings, and would meter by taking a test shot of the target at high ISO, wide open, followed by a series of exposures on Pancro 400 135 using a EOS 1N with exposure times bracketing Bergger's guidance (e.g. +1.3 stops for 10-60 second exposures). "Correct" exposure was based on negative density compared to a short-exposure (1/4 sec) sample. As expected, the film's reciprocity characteristics follow a power law.

    The result was a correction factor of 1.36 (i.e. Corrected Exposure Time = Metered Exposure Time ^ 1.36), determined using a least-squares linear regression of log exposure time.

    Pancro 400 appears to have at least a stop of latitude in both directions, which makes Bergger's guidance totally decent for exposures of metered time less than c. two minutes.

  2. #2
    Drew Wiley
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    Re: Bergger Pancro 400 Reciprocity Characteristics

    You might need to modify that for nominal daylight exposure.

  3. #3

    Re: Bergger Pancro 400 Reciprocity Characteristics

    Not sure precisely of your meaning - this is for long exposures (>1 second). Testing was done with c. 5500K light.

  4. #4
    Drew Wiley
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    Re: Bergger Pancro 400 Reciprocity Characteristics

    OK. You apparently daylight balanced the light.

  5. #5

    Re: Bergger Pancro 400 Reciprocity Characteristics

    Yes - In an otherwise dark room, I used a 3200K tungsten fresnel light with a CTB gel to convert to 5500K (and dim) and another ND gel to dim it further. Decent approximation of moonlight, and also I'm eventually planning to do this for Velvia, Provia, Ektar, and Portra, and want to use an X-Rite target to see how the colors shift for those films with long exposures.

  6. #6
    Drew Wiley
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    Re: Bergger Pancro 400 Reciprocity Characteristics

    I didn't bother to photograph our "blood moon" not long ago. But I did watch it. Within a few hours there were plenty of posted preposterous Fauxtoshoppy scenic composites containing it. I had a suitable lens, but no fast color film.

  7. #7

    Join Date
    Dec 2017
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    Re: Bergger Pancro 400 Reciprocity Characteristics

    Thanks a lot for your effort and providing this useful info.
    I just started using Pancro 400 and was looking for exactly something like this to fill the gaps from Bergger's data sheet.
    Miguel

  8. #8

    Join Date
    Jun 2008
    Location
    Melbourne, Australia
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    Re: Bergger Pancro 400 Reciprocity Characteristics

    This test by Australian photography David Tatnall may help.
    https://viewcameraaustralia.org/2017...00-sheet-film/

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