WalterT AAP will select a double star or stars in a star cluster as the "suitable" star
Walter,
The problem is not as simple as that.
ZWO uses multiple stars to obtain the average star size. The small inset image that it shows is just one of the "star" it has chosen.
So, giving the user the choice is not easy, since you need to give it many stars.
That being said, because they are using multiple stars from various parts of the frame, a system that is not perfectly flat will give inconsistent results. Most of us old timers pick on stars about 1/3 of the way away from the center to focus on; I don't think ZWO does that.
The second big flaw is that the ASIAIR is very poor at rejecting hot pixels. The ZWO algorithm would pick hot pixels over dim stars -- that means it is really bad with telescopes with large f numbers.
Worse still, it is using parabolic matching instead of hyperbolic matching.
Just use a Bahtinov mask on a star about 1/3 of the way from the center if you want good focus. Since it works on diffraction patterns, the Bahtinov mask is hardly affected by atmospheric turbulence, and do not need multiple stars. It is also much more sensitive than depending on HFD. The Bahtinov mask can see changes in focus when the HFD changes by only 10%.
Chen
