Mark Aston replied to the topic 'Tips for Auto-Focus' in the forum. 1 year ago

Hi John,

Can you clarify for me what tools in the focus module best cope with diffraction annuli as the focus is automatically moved in and out of optimum HRF for a scope with central obscuration - in my case an 8” RC?

Reading the evolving discussion between yourself, Peter and Nigel, and looking at the online documentation, I’m not entirely sure whether there is a mechanism in each algorithm to determine the outer diameter of an annulus (donut)? What I am finding with an obviously course focusing iOptron electronic focuser is that EKOS passes a point where it stops measuring the enclosed energy of the donut and limits itself to part of the donut (or indeed determines if can no longer detect a star).

I’m really just looking for guidance on what are the critical variables per implemented algorithm that are most appropriate for obscured catadioptrics?

Many thanks