2 Aug
2009
2 Aug
'09
2:30 p.m.
Some large, professional telescopes have image planes with circles of 100% illumination that are the size of a sheet of typing paper- or larger- designed so that a photographic plate in the 8"x10" size could be used. I believe some modern scopes have even larger circles of 100% illumination for specialized detectors and imagers. What this means is that, say you were sitting in the prime-focus cage of the 200" telescope. You can just hold two identical eyepieces up to your eyes and face the primary mirror for two-eyed views, without any kind of binocular adapter. Or rest them on a piece of glass that occupies the place of the plate-holder, racked in slightly until the eyepieces are in focus. Amazing!