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Thread: LR3 RGB dropper as a densitometer

  1. #1

    LR3 RGB dropper as a densitometer

    Ok...I will admit I was a bit bored this afternoon

    I wanted to find the best devl times for HP5+ in rollo pyro at 800 ei. I shot 5 frames each the exact same in 45. There is a grey card, a pure white envelope in the foreground then the background is all zone 4-1.

    I developed each in one minute increments @ 12min-16min the same way each time. My result was very clear and I like the 14 min the best overall. That should be the end of it

    So in LR3 on the grey card, zone V, at 12 min I get 44.2% on RGB.

    The zone III at 12min is 6.9%

    The grey card, zone v, at the 14min time is 37.0%

    The zone III at 14min is 5.6%

    What exactly does that mean? How do I use that info to help me know what the density is?

    I want to make sure I am picking the best time based on more than my limited opinion
    david

  2. #2

    Join Date
    Jul 2007
    Location
    Austin TX
    Posts
    2,049

    Re: LR3 RGB dropper as a densitometer

    I take it that you scanned the 45s' using LR (means Light Room I hope). If so the dropper is measuring the scanner density not the negative density. You need to make a parametric plot for calibration back to the negative. For that, scan a Stouffer step tablet, or equivalent, with the exact and known scan settings that were used for the 5 negatives.
    Plot stouffer density vs dropper % or better the 0 to 256 dropper values.

    I've not used LR so maybe you can't get 0 to 256 data. Next time you are bored also add a good black card in the scene - good for checking linearity - white to grey to black. Record your spotmeter readings.

    I think this will get you what you need.

    Nate Potter, Austin TX.

  3. #3

    Re: LR3 RGB dropper as a densitometer

    That make sense.....tomorrow am a step wedge will be on the way!

    thanks!
    david

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