Autofocus with differing inward/outward movement


I’m going to be trying to use auto-focusing for first time tonight. During a daylight test run I’ve noticed that the focuser has a measurable difference when moving it outwards vs inwards for the same number of steps. i.e. if i move the focuser outwards 10,000 steps, and then inwards by 10,000 steps, it will keep turning for a couple of seconds after racking all the way in.

Will SGP be able to handle this? I’m not sure how it works under the hood. Does it try and build the V-curve, then use absolute positioning to return to the point of best focus? If so, that’s going to be inaccurate in my case.

Note that this a direct-drive system and there’s no backlash present in the system, so I can’t simply set up backlash compensation.


It does and your AF will be off. SGPro works under the assumption that, for a given session, an absolute position will be very close the the same focus position every time. If your focuser is incapable of being repeatable, we cannot work with it.


Thanks for such a quick response, Ken!

This is a long shot, but… I’m also a software developer, although I do web applications instead of desktop applications and I work in Java / JS.

I don’t suppose there’s any way that I could contribute to SGP, is there? I could implement some different algorithms that handle things like this.

I could try to create an alternate method that identifies the best HFR, and then adjusts the focus position until it reaches that HFR +/- some threshold, using the absolute position calculated in the current process as the starting point.

In my current case, a simple scaling operation may also work.



We appreciate the offer, but SGPro is currently closed source. For legal reasons, only members of the Main Sequence Software LLC may contribute code.