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Old-school refractors normally had a large-diameter stiff sliding sleeve that was used to make large changes to the back focal distance to accommodate eyepiece projection and other odd bits of gear such as filar micrometers. The rack & pinion was for fine focussing.
Modern cookie-cutter refactors are really only set up for CCD's.
Last edited by Wavytone; 30-04-2012 at 01:44 AM.
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