Step size - auto focus settings



I’m confused by the guidance on the help page about step size (understanding autofocus). It says:

“The next step is to measure how far your focuser moves per step. To do this setup a dial indicator on your focuser and set it to zero. Now move your focuser a known amount of steps and and note the change on the dial indicator. You should move your focuser enough so that you can easily note a large change on the dial indicator. Ideally you should move the focuser 20mm or more.
Assuming that moving 1000 steps moved the focuser 40mm then you know that your focuser moves 4 microns (0.004mm) per step.
This means that to move 98 microns takes your focuser roughly 25 steps. This is what you should set your Step Size value to be as you’re guaranteed to sample this value once and only once.”

If moving 1000 steps moved the focuser 40mm, then doesn’t the focuser move 0.04mm per step, not 0.004? Then, to move the focuser 98 microns (or 0.098mm) would take roughly 2.45 steps as opposed to 25.

It might be I’ve stared at the numbers too long but would someone mind clarifying? I’m about the purchase a Lakeside Astro focuser and would like to configure my settings correctly !

Thanks very much,



Your math is correct. I had thought this had been corrected already.


Jared Wellman
Co-Owner and Developer
Main Sequence Software


Thanks, Jared.