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Thread: Reciprocity formulas (for Ilford films)

  1. #51
    Ummm... Yeah
    Join Date
    Jan 2014
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    46

    Re: Reciprocity formulas (for Ilford films)

    There was a simple one, I think it was on darkroomagic.com, that showed a couple films and then a column for conventional films. I've used that with success, it even shows the approximate effects on contrast, as in N+x. I think it was Ralph Lambrecht's site. The site is no longer, it would appear.

  2. #52
    Large Format Rocks ImSoNegative's Avatar
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    Oct 2008
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    McCaysville Georgia
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    1,587

    Re: Reciprocity formulas (for Ilford films)

    I found a great formula that works everytime, not sure if anyone else has posted it yet but here goes: 1.7 multiplied by metered time
    plus .12 multiplied by metered time squared= corrected time, this formula works like a charm for me
    "WOW! Now thats a big camera. By the way, how many megapixels is that thing?"

  3. #53

    Join Date
    Jun 2006
    Location
    Westfield, New Jersey
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    417

    Re: Reciprocity formulas (for Ilford films)

    How does one post excel spreadsheets (.xsl files). I have a S.S. that was based on some formula that I read about on APUG. It gives me good results.

    George

  4. #54

    Join Date
    Feb 2011
    Location
    Brisbane, Australia
    Posts
    279

    Re: Reciprocity formulas (for Ilford films)

    As StoneNYC says - forget it. Just get my App! :-)

    I wish this discussion had been around when I started developing Reciprocity Timer 3 years ago.

    This is the formula my app uses for Delta 100 and for HP5+

    e = (0.51 * (m^1.62)) + m

    where e is actual exposure and m is measured.
    This is based on the Gainer/Bond Method as outlined in the article linked in the first page.
    This yields times very close to Ilford's official charts.

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