calculating exposure when you know the pinhole diameter.

I just read the article G. Penate referred to about calculating exposures,
by calulating the f stop of the pinhole and trying to devine the exposure by
counting f stops from a referral point. It doesn't need to be that hard.
1. Measure the pinhole to film distance and divide by 22. That gives you the
diameter of f22 for that distance.
2 Then calculate the area of this f22 aperture by multiplying half the
diameter x half the diameter x 3.14.
3.Then measure the diameter of the pinhole, using the same measure as you
did before, inches or millimeters both times.
4.Then calculate the area of the pinhole using the same formula.
5. Then divide the area of the pinhole into the area of the F22 aperture you
calulated, and use the result to multiply times the metered exposure at f22.

At an optimal pinhole to film distance of three inches, for instance, the
multiplier is about 120. If the metered exposure at f22 is 1/10 second, the
calculated metered exposure for the pinhole would be 12 seconds. You can
drive yourself batty trying to work it through the f stop comparison method.
Received on Thu Dec 28 17:12:02 2000