Gordon Uber <[EMAIL PROTECTED]> wrote: > Roger, thank you for your post. The Shadow Sharpener being a > pinhole camera, why not replace the gnomon with a pinhole? One then > could center a circle on the image and determine the time from its > position.
To form a good solar image the plane of the pinhole needs to be transverse to the direction to the sun's rays. In fact, I believe near-perpendicularity may be desired. To accomplish this with a classic pinhole, the plane would need to rotate during the course of the day. Perhaps there is some clever scheme that would achieve this pinhole behavior without the need for mechanical intervention, but I don't know what it would be. That's the beauty of using a sphere to form an umbra--it needs no such rotation (although the distance between the sphere and the point where the shadow impinges upon the dial changes as the day progresses). Jim ------------------- ---------------------- -------------------- | Jim Cobb | 540 Arapeen Dr. #100 | [EMAIL PROTECTED] | | Parametric | Salt Lake City, UT | (801)-588-4632 | | Technology Corp. | 84108-1202 | Fax (801)-588-4650 | ------------------- ---------------------- -------------------- It is better to suffer wrong than to do it, and happier to be sometimes cheated than not to trust. -- Samuel Johnson