I have a general question about SGP and it’s ability to successfully perform autofocus with a Newtonian.
For reference, I have a AT65EDQ refractor that I use SGP’s autofocus feature on and it performs flawlessly.
However, using SGP’s autofocus on my Newtonian always gives flawed results. Using a Bahtinov Mask, I get a reference focus point (using a stock focuser and an nSTEP controller unit). Then, when I run SGP’s autofocus routine, I will typically get a focus point about 50 steps off the Bahtinov mask result. In fact, when I put the Bahtinov mask in place after SGP’s autofocus run, it clearly shows an asymmetric pattern. The other thing I note, is that I can’t get a symmetric U-curve when using autofocus. I feel like the HFD algorithm does not seem to perform well with Newtonian stars. I do have a Televue Paracorr Type II corrector and when the scope is in true focus, the stars as nice circular stars across the field of view.
Bottom line, my question is, can SGP autofocus work reliably with Newtonian’s using a coma corrector?