I have a timer that can do .1s. I suppose I want to make a step exposure from white until black, then try the same regimen with different filters? You're right, that does sound like a lot of work.
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I have a timer that can do .1s. I suppose I want to make a step exposure from white until black, then try the same regimen with different filters? You're right, that does sound like a lot of work.
Exactly. The same can be done with one exposure by using a Stouffer step tablet. I suggest to invest in one. It's a small long-time investment with long-time benefits.Quote:
Originally Posted by BetterSense
Ralph,
I presume one can make best use of the Stouffer transmission projection step wedges in conjunction with a densitometer in order to access paper and process characteristics.
Tom.
Look where the curves cross...Quote:
Originally Posted by RalphLambrecht
http://www.darkroomautomation.com/support/mgivrchd.jpg
http://www.darkroomautomation.com/support/mgivfbhd.jpg
http://www.darkroomautomation.com/su...fbwta130hd.jpg
http://www.darkroomautomation.com/su...vfbwtd72hd.jpg
Well I just wasted about 4 decades in the old dark room, printing up a primitive test of my contrast filters, with completely inconclusive results. If you would like to speculate on the results you are welcome to. I think I need to budget a step wedge and in the meantime just figure if it don't print on grade 2, wait.
I printed, from top to bottom, .1, .2, .4, 1, 2, 4, 10, 20, 40, and 80 second exposures. 10 seconds is the first tone that showed up. From left to right, the grade 0, 1, 3, 4, and 5 filters.
http://i109.photobucket.com/albums/n...avon/wedge.jpg
NicolasQuote:
Originally Posted by Nicholas Lindan
Thanks for sharing. The ISO standard sets the speed point to 0.6 >b+f. Your data points tell a different story. They are pretty much all over the place. It hard to make out an accurate intersection point. Ilford's own product literature shows a much better fit to the ISO standard. So did (does) the Agfa and Kodak literature, by the way. My own data, also shows little to no deviation from the manufacture data or the standard. I don't know where your deviation comes from, but these are very rough data curves.
The difference might be that I judge the intersection point(s) after applying a best-fit curve through the data points. Best-fit equations for s-shaped curves are not trivial. I can share my empirical equations with you. They were evaluated by Ilford's Technical Department a while back, and they were impressed with how close the data fit was, especially at toe and shoulder. However, I don't think Excel can handle them. You might need a dedicated graphing program.
Different people taken similar measurements often get very different results. Potential sources for variation might be the spectral sensitivity of the densitometer. The red-content in toned or warm-tone papers was too much for my old Agfa densitometer and always gave skewed results. Other issues are often within the consistency of testing. Test exposures should not be collected and then develop together. That alters the results. Just a few thoughts, the list goes on as you probably know. Again, I can't tell where the difference comes from. Maybe you can share how you did your tests in detail.
However, for this conversation it doesn't matter where the speed point is, because it rarely is where we need it to be for an exposure-correction-free contrast change anyway. Nothing beats a well-made test strip.
Yes, TomQuote:
Originally Posted by Tom Kershaw
But you can make a lot of use of them without a densitometer too. I can tell you, fr example, what ISO grade your filter/material combination produces with a step tablet and without a densitometer. No sweat!
I agree, inconclusive. You might need to budget for a new set of filters too.Quote:
Originally Posted by BetterSense
Maybe its not MG paper? I would think the filters would have all faded the the same pale color to produce those results.
It was fresh MGIV paper. All were exposed on the same sheet, developed at the same time.