1) I use the dimple and sand method, generally in one or two mil brass shim stock. I use a sewing needle and work against a scrap of mat board to produce the dimple, then #400, or even #600, wet-or-dry sandpaper, wet, and try to "sneak up on the size." First rule: it is much easier to make the hole a little bigger than a little smaller!
Originally Posted by edcculus
Thanks to some quasi-professional activities four decades ago, I have a little 50x hand-held microscope with a direct measuring reticle to check small dimensions, so I use that along the way. I believe others use a scanner or enlarger to try to measure.
2) That f/22 multiplier is a handy output from Pinhole Designer. You take the light meter reading of shutter speed at f/22 and multiply it by that factor. P.D. saves doing the math to get the multiplier, which is necessary because few meters go to f/275 or whatever. I usually generate a pocket-sized table for the multiplied shutter speeds to avoid calculators in the field. P.D. can even output such a table with or without reciprocity compensation for a number of films. Unfortunately it hasn't been updated in a long time, so some newer films are not in it. But all that stuff can be generated with generic tools (or pencil and paper!!!)