My main problem with autofocus is when it identifies noisy pixels as if they were tiny stars - and that throws off the HFD calculation. I’m not sure how nebulosity rejection works exactly - but if instead we could enter the minimum HFD of a real star, in arc-seconds, then those small stars would be rejected from the star measurement statistics - and it would only use “real” stars that are above the minimum size.
Neb. rejection does work - but it requires tuning, possibly to each object. But I know I’ll never have a real star under about 1.4" - so I don’t want them in the average. Then I don’t think the neb. rejection would be as critical.