Doug S replied to the topic 'Question about focuser module' in the forum. 1 month ago

A couple of thoughts here. First, can you post your electronic focuser model? 16K steps/revolution is quite a bit! Could this be a typo? Second, it's been my experience that motor vendors typically recommend *not* using the fine focus shaft for attaching the motor. In your case, with 16K counts/rev, you may find this will be problematic (overkill on resolution). What you REALLY want is to match your motor counts per revolution and distance of focuser drawtube motion (commonly referred to as thread pitch) such that the number of motor counts per micron (motor + focuser) is well matched to your telescope's Critical Focus Zone (which is a function of your telescope's aperture and f-ratio).

You've got motor counts per revolution (but it should be verified). Your next unknown to resolve should be to know how far (microns) your telescope's focuser drawtube moves per knob revolution. Once you know this, you can detemine motor counts/micron. That's an important number because you can then evaluate it against your telescope's CFZ . You want enough "resolution" to have at least several counts through the CFZ. Too many is overkill, and too few will have you jumping over the CFZ.

If you're confused about CFZ size and you haven't already looked at this page, it should help:
www.goldastro.com/goldfocus/ncfz.php
Don't let the equation scare you.... If you use seeing of ~2 arcsecs, and a focus tolerance of say 7%, you can calculate a good value for CFZ. Finding your focuser drawtube distance per knob revolution will finally get to your counts/micron. Good luck...
Cheers, Doug

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