A very good friend of mine, uses a H18 CCD camera with this Celestron 8" SCT.He has a curious problem, and I am hoping some of you might have an answer.If you look at the attached image you will see what I mean.My theory is. We are seeing a ghost image, of the SCT corrector, and secondary.But what is the cause and is there a fix.The SCT has been flocked and is carefully collimated.
It may not be useful, but here’s my thoughts.1. It looks like a very out of focus star as seen visually in my Celestron C8.2. It’s off centre.Have you got an artificial star just outside the field of view, and rather closer than infinity?Maybe a chrome screw on the tube. An over long screw securing the corrector plate might do it, on my old C8 they poke though the tube and just stick out on the inside.Roy