What is the best size for the pinhole?
The size of hole you need depends on the kind of effect you want to get. Many of us calculate the “optimum” size and then depart (or not) from it, in order to experiment. There are many formulas to calculate the “optimum” size. Optimum, in this case, means the hole that gives the “sharpest” pictures. Incidentally, the sharpest pictures may or may not be the “best” pictures for you. The formula I use is: Optimum pinhole diameter in inches = 0.0073 * SQR (focal length in inches) SQR stands for square root. For metric system the formula becomes: Pinhole diameter = 0.03679 * SQR (focal length) where diameter and focal length are in millimeters Once you know the size of pinhole you will use, find the f/stop of your camera by dividing the focal length by the diameter. Obviously, both values must be in the same unit of measurement. f/stop = focal length / diameter More likely than not, the f/stop won’t coincide with a full stop. Since the progression of f/stops is not linear, to find where ex
