I just ordered my first 21 step Stouffer's step tablet and I want to make sure I understand how to use it properly when testing papers for the total exposure/brightness range?
What is the proper way to find the right expsosure to use when testing papers?
Thank you for your help.
Contact it to the paper tightly so no light leaks around. If light leaks around the dense strips this will mess up readings. If you just want to measure contrast, expose so the entire scale fits in the step tab. If you want to compare paper speeds, you need to do some trial to get the correct exposure time so your speed point shows up in all the tests without altering the time.
Cheap and dirty way to determine the conrast. Count the strips between the darkest and lightest. Multiply by 15 to get ISO(R).
So if 5 gray strips are present, 5 x 15 = ISO(R) = 75 = about 3.5 grade.
How not to do it. This one was not held down tight and light leaked around the edge. This one is from taking the color head and setting right on the paper with the step wedge between. The wedge really needs to be held flat. With collimated light (When projecting light from a lens), this bleed is less likely to occur.
Very helpful, thank you.
How do I first determine the correct exposure to use to expose the tablet for my paper/developer combination?
I assume if I do exposure tests in small increments on the paper alone, that will get me close to the proper time to use. Normally I would use an unexposed but developed sheet of film to lay over the paper when doing the small incremental exposures, but the step tablet doesn't have that blank area I think? I just want to make sure I am doing this correctly...
Thank you.
Originally Posted by ic-racer
Brings back a memory when I was a student at RIT in the mid 1970s. Went something like this: I was taking a Materials and Process course under Hollis Todd. About midway through the semester, Hollis Todd said in class that the contrast of a paper did not change with the developing times, only the reflection densities got higher. I stopped by his office and told him that I begged to differ with this teaching (published in his book Photographic Sensitometry). He looked at me and told me to prove it. Spent the next week or two conducting test. Using one enlarging paper (most probably Varigam or Varilour), with a step wedge to calculate the paper's contrasts for different developing times. My readings indicated that the contrast did change with increased development times. Wrote it all up and quite nervously presented my findings to him. He sat back in his office chair and read my findings. Then said something like "you know what this means.... you just earned an A for the course." He told me that when he and written his book (probably 6+ years earlier) his teaching was correct for graded papers, but it was not correct for the VC paper that I was using. From then on I would stop by his office every week to engage in a great academic discussion. Still have one of the test strips that I made back then (attached).
Interesting...
FWIW, my tests with different papers and developing times have all shown that extra development basically increases paper speed, but not contrast. I imagine different papers react differently.
To the OP:
Your exposure for the step tablet just has to be enough that you have both max. black and white somewhere on the scale. You use the step tablet to see how contrasty your paper is or to keep tabs on process (developer exhaustion). You don't use it to determine a print exposure for actual printing.
Best,
Doremus
Doremus, just an speculation, perhaps (to be checked) this may depend on developer and of base grade. Supose that we expose basicly the green sensitive component of the emulsion, if development is more energic perhaps more infective development may take place from crystals of the blue-only sensitive component... (in fact there are 3 components or more in the VC paper)
After developing to completion further infective development may take place, perhaps... Again, this is only a reasoning...
Thanks, Doremus, that makes sense.
I was under the impression if I found an exposure time that produced DMAX on the step wedge that this time was my standard printing time or as Fred Picker used to say the Proper Proof time. Am I misunderstanding this concept? If so, please help me learn so I can improve.
What is ISO(R)? This is a means of comparing different manufacturers’ contrast grades in absolute terms. It is the logarithm of the exposure range required to give a full tonal range, expressed to two significant figures, with the decimal point removed. Typical figures might be Grade 5 = ISO(R) 40 to 45; Grade 4 = ISO(R) 60 to 70; Grade 3 = ISO(R) 80 to 90; Grade 2 = ISO(R) 100 to 110; Grade 1 = ISO(R) 120 to 130; Grade 0 = ISO(R) 140 to 150; Grade 00 = ISO(R) 160 to 180.
The density wedge will progressively give more and more exposure to determine the maximum density for you. Now, if you read the strips with a reflection densitometer, you don't use the "most dark" and "most light" strips to do the ISO(R) calculation or the ISO speed calculations. Just like with film, the density (speed point) is just a little away from maximum black or white.
I can't find the ISO paper off hand but the paper speeds are based on work represented in this graph from Loyd, 1942 that shows the useful range (which the ISO(R) contrast is based) is not at the exact black and white points. It is complicated to find those points, thus the recommendation to just skip the "near black" and "Near white" strips on the processed paper.
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