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A Sensitometer Tablet — Ives and Crahtree 745
a density sample should be chosen which is equal approximately, to the heaviest density (No. 20) produced in the printer light change test minus the lightest but one (No. 2). These should be mounted temporarily in the tablet.
The correct exposure conditions in the sensitometer should then be chosen by making flash exposures through the tablet with the illumination regulated to give varying intensities and, by flashing a part of the same strip of film on the printer, set at step No. 20. If the sensitometer exposure is correct, the No. 20 step on the printer and sensitometer will produce equal densities when the film strips are developed together under the conditions stated previously. If at this exposure the density given by the No. 2 step of the sensitometer is too low, the film sample in the tablet should be replaced by another of less density and vice verse. When the correct density of this tablet step No. 2 is found, density samples for the eight intermediate steps can be chosen.
4. Tentative Choice of Intermediate Tablet Steps At this point the set of flash densities given by the printer is consulted for the purpose of estimating an average exposure difference and for noting irregularities at any point.
Ordinarily the exposure differences are such as to produce equal density differences. This will be noted by the fact that the same density superimposed over any one of the flash densities made in the printer tests makes a combined density equal to that produced by the next higher printer step. If such is the case, it will be convenient to construct a trial tablet of uniform density gradient. By selecting a suitable density sample which will be equal to the average density difference between successive tablet steps, a piece of film can be selected for each tablet step by matching with the next lower step over which has been placed the density difference sample. A few trials may be necessary to find the correct average density difference, but this can be checked by placing, one over another, as many thicknesses of this density as the number minus one of the steps in the tablet, when their total density will be equal approximately to that of the tablet step previously chosen. Thus, a tentative tablet is completed.
If the differences in density between the test samples exposed at consecutive light change steps on the printer are unequal, it will be necessary to deviate accordingly from the regularity of increase