I’m trying to get a feel for using a flash gun to expose paper negatives.
Rather than trial and error I’m initially using logic to give me a start point!!!!
Therefore, assuming:-
1] the stated GN of the flashgun is correct and repeatable
2] the ISO value adopted for the paper used for the paper negative is correct and constant.
3] the flashgun GN decreases by the square root of 2 for each halving of the ISO number. (ie GN 33 for 100 ISO becomes GN24 for iSO 50 etc – light falls off at root2 times the increase in distance)
Therefore assuming unity for the (any flash gun) GN at 100 ISO, then the correcting factors are:
0.707, 0.500, 0.354, 0.250 and 0.176 for ISO value of 50 down to 3.
So for a GN of 48 [meters @ 100 ISO], the corrected GN for 3 ISO is 9 which gives 1.6m @ f5.6
Is my logic correct or am I missing something that effects the practice of using a flashgun for paper negatives?????
Regards
Tony
PS Mod, move if in wrong forum
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