I know the focus settings can trim down the outer margins before measuring the star HFD. With my Tak scopes, the best place to focus on is about half way out from the center. One suggestion would be to also exclude a middle proportion too, effectively creating a rectangular donut of measured stars.
For the greater good, it also occurred this may be a simple way of avoiding the focusing issues with HFD measurement of bright central galaxy/nebulae and in particular, globular clusters, by excluding them from the HFD measurement.
Hey Buzz, this have been asked SO many times before…
Tak scopes and fast Newts will really benefit from this, but unfortunately this feature neglected
+1 on that
I’m guessing it might be accomplished by either cropping out the middle part of the image… or disregarding the HFD measurements from the central portion when working out the overall HFD for the image.