[codemonkey (Lee)]

Originally Posted by xelasnave

Keep seeking a solution but startools has a feature "repair" which I find excellent on most occassions to fix star problems. You may find you can use data that might be thrown out.
Alex

Thanks Alex and Martin, that's a good idea; better than throwing out data!

Originally Posted by Imme

Do you use a field flattener?

I spent months looking for the cause of elongated stars and it ended up being a lens in my flattener

Thanks Jon. I don't use a flattener as such, but I do have a coma corrector so the same thing applies really. I think if it was the coma corrector the orientation would have stayed the same with respect to the image when I did the rotation test, because the camera and coma corrector retained their relative positions.

Originally Posted by Joshua Bunn

Hi Lee,
This also suggests it could be CCD tilt, in my experience. What do you think?


Josh

Thanks Josh. I had thought that tilt would manifest in an aberration that remains fixed relative to the image when I rotate the camera, no?

I have noticed another difference between the images I took during the rotation tests... I notice that at one orientation the focus position is different to another, which suggests a collimation/tilt issue. I've been very particular with the autocollimator lately and ensuring it's being used as close to the focal plane as I can get it in an effort to ensure that there's no focuser axis misalignment, which I've read can cause similar issues.

My only thought now is that the focuser is not square to the tube (which I have read does not matter, thus why I haven't considered it before)... maybe that means that at one orientation the image will be better than at other orientations?

I've now been in contact with Teleskop Service in Germany who were very quick to respond. Based off my tests they think it's astigmatism in the secondary or its mounting (though they're perplexed because they tested the mirror on their optical bench... suggests mounting issues to me). They're intending to send me a new secondary.

I'm going to try squaring the focuser before I accept their replacement and if that gives me no joy then I'll go down the replacement route. Either way, I think I've narrowed it down to two potential causes and have solutions for both so I feel this might finally be coming to an end...