icsn offer this:
Quote Originally Posted by DWThomas View Post
Doesn't sound good. The ideal pinhole is a knife edge; a hole in an infinitesimally thick plate. Any length will constrict the width of the field of view. The ray tracing explanations in one of the posts above will illustrate why. Using what is in effect, a tube, most rays angled off the axis will be blocked.

DaveT