LR3 RGB dropper as a densitometer

[atlcruiser]

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 :)

[Nathan Potter]

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.

[atlcruiser]

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

thanks!