Camera+Film+FilmDeveloper Process Control idea for Zone System followers

Bill Burk said:

PeterB,

I don't know if you saw this thread where we explored a test strip maker. I found it remarkably easy to do.

(there was a url link here which no longer exists)

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Not until I just spent the last 30 minutes digesting it ! You are more geeky than me Bill , and I have 2 t-shirts and a cap with the word GΣΣK written on them (given to me by my lovely wife).

The only eBay search I've had running for about the last year is one for a sensitometer, and after reading that thread I have even less of an idea which brand/model to look out for. I hope your EG&G sensitometer is proving useful, you certainly spent some time getting to work it out. Surely there have been ones made since, that are at least as accurate (and feature-full) but not so old fashioned.

I'd prefer not to use my enlarger to expose a step tablet into my film because I'd then want to test my enlarger lamp response/warm up time at different filament temperatures and then try to control for that which doesn't sound too appealing. I have already tested my camera's shutter speeds (and had the CLA guy do it too) so I'm more comfortable with those being repeatable and accurate to within 5-10% (my intended accuracy of this Process test).

Perhaps if I get a sensitometer my quick Process Test will change to using that, but for now I will use my camera, and either a Tx step tablet in the manner I describe above or a reflection test target illuminated with either the sun at a similar time of the day (or an artificial light source) and vary the amount of light by adjusting the aperture over its entire range (the original idea I posed with this thread and the 'easiest' to do if one doesn't have access to a step tablet or sensitometer.)

rgds
Peter

Bill Burk said:

First thing that comes to mind is... Color separation negatives through the blue filter have to be developed longer than the other separations because blue light results in lower gamma. (That's an explanation I've read, others may corroborate or dispute). Maybe the light on the white towel had more blue than the cream wall.

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Bill, I just found this effect you thought of reported (there was a url link here which no longer exists) by Stephen and is called the Gamma-Lamba effect . The magnitude of my results correlate closely to those reported by Kodak for Tri-X.

In fact UV photography suffers from this effect and when I photographed the white towel it would have had optical brighteners from my washing liquid (that fluoresce UV) and possibly further amplified the effect

What a cool serendipitous discovery I stumbled upon in my testing.

rgds
Peter

PeterB said:

when I photographed the white towel it would have had optical brighteners from my washing liquid (that fluoresce UV) and possibly further amplified the effect

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On second thoughts the optical brighteners wouldn't have amplified this gamma-lambda effect I observed as it wouldn't have created proportionally more blue light. The blue cast would have come from the fact that the white towel was in shade and only exposed to blue sky while the cream wall (already 'warmer' than white) was exposed to more direct sunlight which has a warmer colour temperature (see ct chart here)

rgds
Peter