From: ryberg (ryberg@mind.net)
Date: 04/12/02-05:36:27 PM Z
I suspect that the formula you read didn't translate to the simple code of
an email. Surely it must reformulate to:
Divide the f stop of the pinhole (f420 in your example) by some fstop on
your meter (keep things easy and pick f42). You'll get 10. Square this
number (10 times 10 is 100). This is the exposure factor between the two
apertures. Now multiply the metered exposure by this factor. If the meter
said one-fifth of a second at f42 then one-fifth times 100 (that would be
100 fifths or 20 seconds) is your calculated exposure.
As has been pointed out, this does not allow for reciprocity failure.
Start by doubling the time calculated and adjust as your experience warrents
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