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RE: Appendix

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Posted by Kip Crawford on October 17, 2000 14:37:48 UTC

A good 4.5" reflector should be at least a f/9 ratio which is a 39.5" focal length. At f/4 or 5 which is between 18" to 25" (short tube, fast focus). The reflector uses a primary mirror that reflects the focus to a 45 degree secondary mirror that goes to the eyepiece. Quite simple really. The more elaborate type scope is the Schmidt-Cassegrain (SCT) which uses a corrector lens which enables the scope to have a long focal on a short tube.

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