Re: Focal length in use by Charon

elliottb@uwec.edu Mar 24, 2001

Hi Bill and Charon users.

The focal length that Charon finds with many S-C telescopes will depend on
the spacing of the mirrors in the telescope and that is set by the stuff
you have attached to the back of the telescope and how far out you have to
bring the image to focus on your CCD chip. The farther out you move the
focal point the longer the effective focal length becomes. With the
Schmidt-Cassegrains a large variation in focal position is obtained by
being able to move the primary mirror forward and back to attain a good
focus. This versatility is a very nice feature but does change the focal
length and degrades the image quality somewhat. Charon's determination of
the effective focal length is by far the best value to use.

Regards,

Bob Elliott
750 Fall Creek