Here's a down and dirty formula for a simple pinhole camera made from a
Quaker Oats Oatmeal Box or a Grits box. The grits box is better because it
still uses (last time I checked) a cardboard top instead of a plastic one
which needs to be lightproofed. Anyway, for the diameter of the tube use a
standard pin and "drill" a .3mm hole in a piece of brass or copper foil
(about halfway up the TIP of the pin) and sand both sides of the metal
smooth. This eliminates light diffraction. I have used 30 sec. as a
starting point for full sun and 45 sec. to 1 min on overcast days. I've got
a mathmatical formula for figuring out aperture diameter based on focal
length of box. I'll post it for anyone if you'd like. Good Luck!!
Mark Larson, Art Teacher
Lincoln High School
1801 16th Street So.
Wisconsin Rapids, WI 54494