Hej Doug,

I'd say that isn't uncommon for standard rack&pinion focusers. And there's no real issue with that, IMO. That is why we use a stepper motor that has no problem doing single step accuracy. The 10:1 is for "clumsy fingers", but always has the chance of inherent slip, so it's really not recommended if you want reproducible focus-by-number. There's no gain of accuracy in having 'big numbers' when using a stepper motor.

As for the low 0.75μ/rev, that sounds to me like it is the movement of the main mirror, not the movement of the focus position, so that would get a magnification of about 10 from the secondary re-imaging, depending on your type of optics. Would still lead to quite large numbers, but that is really just focuser specific. A Crayford likely also has smaller step sizes than a R&P.

Cheers & Happy New Year!

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