William Erickson wrote: > Thanks. Why didn't I think of that? I'm still curious about whether there's > a formula for determining focal length from sphere diameter.
There definitely is. I don't remember it (college physics was 25 years ago...). Almost any book on optics at your local public libraray should have it. (It is something very simple like "the focal length is equal to the diameter" or something like that.) Mike Vande Bunt
