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I am making a spreadsheet to calculate exposure times for a
pinhole camera for a friend. I had no problem converting meter readings at a
given f-stop (f/22) to the pinhole f-stop (f/220). But I am not sure how to
correct for recipricocity failure. Looking at the graph for Ilford films I came
up with a formula which seems to work within the range of times they show on
their graph. But the times I get when converting longer times seems way to long.
For instance if the metered exposure corrected for the pinhole is 13 1/2 minutes
the recipricocty corrected exposure is 5 1/2 hours according to my calculations.
This does not seem right. I don't have a lot of experience with very long
exposures . If there is anyone that does could you please tell me if this sounds
correct.
Kenith Ryan
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