I ordered a set of five third-party body caps, the intention is to make a pinhole body cap for EF/EFS. So if I did the math for non-macro right, the hole size is as such: pinhole diameter = SQRT(2.44 · focal length · wavelength) Center of the visible light spectrum is around 550nm, or 0.00055mm. Flange distance on a Canon EOS is 44mm, presumably to the back side of the body cap. This yields a pinhole size 0.243mm. Assuming the body cap is around 4mm thick, the focal length becomes 48mm, this means pinhole is 0.254mm. The 2.44 number came from a youtube video describing balancing the problems of too-small and too-large pinholes. It applies when the subject is sufficiently distant that as a divisor it approaches irrevelance, versus requiring consideration for macro photography. So, my game-plan: Frst I'm going to take some measurements of the body cap and some general measurements on the camera, confirm my numbers, and attempt to find-center on the body cap. Second, I'm going to look through my drill bits including lathe center-drills, see if I have anything whose point is anywhere close enough. If not then I may have to order something. Grainger has small drills in the ~0.250mm size, as low as $10, and there are whole sets on Amazon that are inexpensive with a variety of sizes. Third, I'm going to determine if I can make a pinhole accurately in the bare plastic body cap itself, or if I need to make the pinhole in another material and set that into the body cap. I'd rather not use a separate material if I can avoid it. Fourth, I'd rather hog-out the cone of material from the inside of the body cap (hence the ~48mm calculation) such that the only thing visible on the front of the body cap is the tiniest of pinholes, so probably use some kind of counter-sink bit to drill down to just below the outer face of the body cap, if I am avoiding using a separate material. If I mess this up I can always make the hole bigger and then use separate material.