Doug S replied to the topic 'Celestron focus motor' in the forum. 3 years ago

@mhammady: The 8SE appears to have a thread pitch of 24 threads/inch or 0.94488 threads/mm (1.0583mm/thread(or 1 rev)). You're at F10, so your CFZ is on the order of 2.44*10^2 (244um). If you were to use the Celestron (1k cnts/rev), the math works out to 1.058um / count or 230 counts "length" for the CFZ. The ASI has 5760 cnts/rev, which works out to 0.1837um/count (1328 counts CFZ width). That's overkill unless you know you'll be adding a focal reducer. As Bart indirectly points out, at F10 and 200 counts/rev, you'd have a CFZ length of 45 counts. That seems "skinny" to me. 400 counts/rev would give you 90 counts CFZ length. 1000 would give you room for that focal reducer you're going to want ;-) . My 2 cents. Cheers, Doug.

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