Robust focuser backlash compensation

Hey Guys,

I’ve noticed a few posts recently about not being able to achieve good focus and had a thought about how this could be made more robust for those that have inconsistent focuser systems.

If you do the focus as a two pass process with your first pass bring your normal V-curve, then rack the focuser back out and take some additional samples you could determine if the new line for those samples is shifted relative to the original lines and project a new critical focus sample point. I’ve included a picture below showing what I mean.

Ideally you would sample until you were getting close to a projected best focus HFR value and then determine how the new line is shifted relative to the previous and rack the focuser to the rest of the way to the calculated new critical focus position.

David Ault

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