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The following issue came up on another forum and I wanted o ask the question here to get Phil’s opinion and see if I am on the right track. The issue is this. We are developing with a pyro staining developer and using the UV mode to read the test film densities for alternative printing with UV light. In checking readings with a densitometer I found that the Stouffer TP 45 step wedge has a different reading when read in Visual Mode as compared to UV mode. In Visual the step wedge ranges from mode ranges from 0.05 at Step 1 to 3.05 at Step 21. In UV mode the readings range from 0.10 at Step 1 to 2.87 at Step 21.
So, what step tablet reading should be used in the WinPlotter program, assuming that the final measurements of the test negatives are to be read in UV mode. My reasoning is that the UV mode readings should be used, otherwise the units of measurement on the X and y axis will be of unequal length. So I tested the idea by running the Plotter program again with a film that I had previously tested, comparing results with step tablet densities read in Visual and UV modes.
As I suspected there was a significant different in the curves as plotted depending on which of the step table readings was used. The differences affected effective film speed, CI, and SBR values. To be precise, here is the difference when both calculations are made base on 10 minutes of development.
Step Tablet One, or the Default, made with Visual Reading: EFS=160, CI =.69, and SBR=8.3
Step Tablet Two, or the one made with UV reading: EFS=100, CI=.76, and SBR=7.5.
So I concluded that you need to read the densities of the step tablet that will be used to expose your test negatives in the mode that will be used to measure these negatives. My reasoning is that measurements on the X-axis and y-axis need to be the same, i.e., taken with the same measuring instrument or mode of measurement. If not, the distance between equal units of log measurement would have to be different on the x and y axis. In the case of the example cited the step tablet measured in UV mode had a total DR of 2.77 (2.98 - .10) in contrast to the DR of the Visual mode reading of 3.0 (3.05 - 0.05). But the actual range of 2.77 is being expanded to a physical range on the X-axis of log 3.0 units. As one could predict this expansion of the X axis will result in a shallower slope, i.e. lower CI, if the plotting is based on the Visual mode reading.
So this leads me to believe that one of the purposes of plugging the step wedge densities into the plotter program is is to establish a common unit of log density for the x and y axis.
Is my reasoning sound here or am I off base?
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