[EMAIL PROTECTED] writes: > Oy vey! Maybe this will restart the "Shadow Sharpener" thread going > again! Sounds like quite a project-good luck. I would like to > suggest that if you use a pin-hole, that the aperture be parallel to > the dial face. This may seem obvious, but it wasn't obvious to me 2 > years ago. This way a round hole will always cast a round image, > and will not spread into an ellipse as the angle of the sun changes.
It is true that parallel rays shining through a circular hole will produce a circular image on a flat surface parallel to the hole. But an extended source shining through a pinhole will produce an elliptical image (unless the optical axis is normal to the surface). Consequently, the edges will be fuzzier in one direction than the other, whether or not you want to consider that to be an elliptical image. I suspect that a circular hole parallel to the surface is still the "best" compromise. Regards, Art Carlson
