Focusing
I don't like the little .75" diameter focusing knob on the Celestron so I had built a bigger one from a plastic pulley, built up with epoxy and attached to the Celestron knob with a set-screw which worked admirably, but looked really cheesy. As I'm in the planning stages of a motorized focus setup I needed something a bit 'better' and when Dave Rubenhagen, my machinist buddy, saw my effort he just HAD to build a proper expander for it. This started life as a piece of 1/2" aluminum plate and is machined to fit on the Celestron knob (suitably turned to knock down 1/2" of the knurling). Around the outside is a rubber belt so that when I add my motorization the motor has something to turn against. For now it's nicely 'non-slip'.
Instructions on the build are here.
NOTE ON FOCUSING
Since then I've added a motor to drive the focus expander... easy focusing with no jitters whatsoever
Collimating
I've never liked how SCT's handle collimating. It's just cheap. On my Celestar the secondary plate sits on a center stud and the three colimating screws just sorta hang there. This means that at some points one of the screws can be inserted with no contact with the secondary carrier in the corrector plate. A simple fix for this is to put a spring in the carrier, around the center stud, to put tension on the secondary plate. Also, I replaced the Celestron hex screws with brass thumb screws (a la Bob's Knobs... but better) It makes collimating much simpler.
To read my page on collimating knobs CLICK HERE.
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