PHD and getting perfectly round stars

[Stephen]

Now that definitely looks like a flatness issue, but at the same time it looks nothing like the aberrations you showed previously?

Are you using the right flattener for the scope?

Could need a small spacer (or reduction!) but equally could be a case of just out of focus on the central stars. Some flatteners don't work fully I think if focus is not spot (and I mean perfect) on.

[Flea77]

Yep, the "after" images are from the same image as the original.

I am using one of the only flatteners I could find that said it was for my f number (f7 scope) that had 2" filter threads on it (which is an absolute deal breaker for me, no filter threads, I don't want it, period). The HoTech field flattener says it is for f5 to f8 scopes.

It will not go shorter, but I can add spacers to make it longer. Since I can only go one direction it can't hurt :-)

Allan

[rfdesigner]

good news.

Nasty little problem you've had there, please post up the result after you've tried fiddling with the corrector spacing.

Clear skys

Derek

[dave_galera]

Allan,

There is an exact distance (backfocus) required from the reducer/flattener to the camera sensor, this distance is critical on refractors, well it is on Tak scopes, so you will have to find this measurement and space the camera out to get it correct. If this distance is not correct you are going to get all sorts of problems.

[FraserClarke]

Now that's depressing, something I can do nothing about. Interestingly enough though, I see the same thing roughly with targets directly overhead.

Well that means it's not atmospheric dispersion, as that is a function of target altitude.