Quote Originally Posted by Ole
The "image" is formed by the light moving in straight lines. So the resolution is inversely proportional to the size of the hole. Same as with lenses; just about anything gives a decent enough image at f:90..
Not true. Consider the angles involved. If the light rays did not have to be "bent" at some point in the process, the only way an image could be formed would be if the lens - uh .. "pinhole" was at the same distance from the subject as it was from the "plane of ... uh... "film" - at a 1:1 ratio.. then all rays would be -- un-refracted is the best term.

There are a lot of optical characteristics that are affected by a decreased aperture, depth of focus, being one - but not necessarily "resolution". Not all lens resolution is improved by reducing the aperture, however ... It all depends on the design. A *very* fast lens will provide *optimum* resoultion at apertures nearer the most wide open, as that is where performance is expected and where it was designed to be .... "general use" lenses, near the "middle" apertures and certain "process" and enlarging lenses - close to the smallest apertures.

It is awfully difficult to describe all this in "three words or less". It is an interesting task to become familar with the "old days" of lens design - before computers, when lens manufactures had *crews* of people involved in "ray tracing" and calculating where the plane of focus would be - and curvature of focus - and so many other characteristics. Let me tell you about "Snell's law" and indices of refraction....