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Thread: Ilford - new reciprocity failure compensation factors

  1. #1

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    Ilford - new reciprocity failure compensation factors

    As you may have noticed, the reciprocity failure compensation graphs in Ilford's film literature are generic. A few years ago I had a discussion with Harman tech service about how frankly lousy Ilford's and Kodak's low intensity reciprocity failure (LIRF) compensation charts were/are. After some back and forth they decided to carry out new, film-specific LIRF testing. I followed along as Harman went through this process and the revised factors have now been publicly released. Notice most of the factors are substantially different than the old chart indicated.

    https://www.ilfordphoto.com/wp/wp-co...mpensation.pdf

  2. #2

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    Re: Ilford - new reciprocity failure compensation factors

    This doesn't seem to work for exposure times of one second or less. After my own tests, I never applied corrections at times of 1/4, 1/2, 1 sec but the old literature suggested doing so and many good negatives were spoiled as a result.

  3. #3
    Hack Pawlowski6132's Avatar
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    Re: Ilford - new reciprocity failure compensation factors

    Wow. Cool.

    Good job Michael.

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    Re: Ilford - new reciprocity failure compensation factors

    Good job Michael, can you work on Kodak now :-)

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    Re: Ilford - new reciprocity failure compensation factors

    Great to know it !

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    Re: Ilford - new reciprocity failure compensation factors

    After reading it, IMHO it is also good they point those important factors:


    "For very long exposures at very low light levels then
    some other variables come in to play such as the
    accuracy of the light measurement. This means that
    some trial and error may be required.

    You may also find that the contrast is increased with
    long exposures. This is because of the light level
    difference in light levels between highlights and
    shadows in the image in effect giving different
    reciprocity failure within the image. If this occurs, then
    pulling the development may be required (reducing
    development time) but will depend on the range of light
    levels in the image."

    The "some other variables ...such..." wording disclaimer is important. It is not mentioned, but I guess that also "other variables" as film batch and film aging may play a role. About metering, it can also be really challenging, for separate zones, and including flare from highlights to the shadows...

    Perhaps because that complexity... manufacturers were not giving precise factors to encourage practical trials, rather than encouraging the counter... this is the easy way.

    So IMHO this document is the right way, giving accurate factors, but still warning about the practical challenges a photographer may find.

  7. #7

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    Re: Ilford - new reciprocity failure compensation factors

    Quote Originally Posted by IanBarber View Post
    Good job Michael, can you work on Kodak now :-)
    Kodak gives separate LIRF corrections for each film, but not the factor. In general Kodak shows excellent technical documentation, I like that.

    Ilford is prone to give more "photographer friendly" information, IMHO, also not a bad thing.


    Anyway I like the LIRF specs from Acros

    Sadly they are going to kill LF Acros. To me this is a big mistake coming from earlier big mistakes...

  8. #8
    baro-nite's Avatar
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    Re: Ilford - new reciprocity failure compensation factors

    Thanks very much indeed. Interesting to compare Ilford's new LIRF compensation factors with the work Howard Bond did in 2003. He was trying to retain density in Zone III, and what he found for HP5+ is less compensation than these new factors indicate. But they're in the same ballpark, which can't be said for the old Ilford graph (which is still in the film data sheets). I have added tables based on the new factors to my film notebook.

  9. #9

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    Re: Ilford - new reciprocity failure compensation factors

    Quote Originally Posted by Pere Casals View Post

    The "some other variables ...such..." wording disclaimer is important. It is not mentioned, but I guess that also "other variables" as film batch and film aging may play a role. About metering, it can also be really challenging, for separate zones, and including flare from highlights to the shadows...
    Could the other variables include environmental factors like the spectral qualities of the light being captured?

  10. #10
    tgtaylor's Avatar
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    Re: Ilford - new reciprocity failure compensation factors

    I'd take the new reciprocity factors with a heavy grain of salt. I have had excellent results using Ilford's published reciprocity graph for Delta 100. For example the negative for this salt print http://spiritsofsilver.com/yahoo_sit...5649_large.jpg was metered at 30 seconds which translated to 160 seconds on the graph. Important exposure considerations were the light on the water, the clock, and the office lights. Plugging 30 seconds into the new equation gives an exposure of 73 seconds - almost half that of the old. If I had cut the exposure by 1/2 I would not have gotten the print that I ended up with which is exactly as I visualized it when I took it.

    Thomas

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