[Joshua Bunn (Joshua)]

thankyou to you all for your replies.

Originally Posted by PRejto

Josh,

Sorry you are having so much trouble.

Have you tried rotating the camera 90 degrees and repeating the experiment?

Can you eliminate the secondary support? That is, have you slewed to a position where you get elongation and re-checked collimation? Could it be focuser shift?

Also, maybe you should turn off anything in software that might be contributiing such as PEC and Protrack, and then take even shorter exposures. Maybe your model isn't great at 40 degrees and Protrack is moving the scope??? Also, if you take much longer exposures in an area where you get distortion does the distortion increase at all over time?

PS You should have come to AAIC because Rick Hendrick was there and maybe he would have been able to help! There were more experts in attendance than you could shake a stick at!!!

Peter

Hi Peter,

I think i tried rotating the camera some months ago, but i will definetly do it again and see what the results are.

I have slewed to different positions in the sky (where the problem areas are) and the collimation seems to hold by looking at the defocused star and looking for concentric circles. The focuser is on a lead screw which stops focuser travel, but i cant be sure its not shifting sideways with gravity, there was also something else that happened after moving the focuser that i need to retest.

Ill have to take a longer exposure and see the results. But, the pictures i posted here were 60 sec guided, and the guide graphs inducate guiding to 0.1 - 0.6 of a pixel at 2.5 m FL. for 1.2 arcsec / pix. image scale.

yeah, would have been good to be there, ive had to talk to Rick via phone about this issue.

Originally Posted by gregbradley

Have you talked with Rick Hedrick about this from Planewave?

Something in the scope is shifting. Secondary, primary, focuser, possibly the corrector.

Greg.

Thanks Greg,

Yes ive been on the phone and email to Rick and will be again when he gets back to the US.

I can rule out the corrector as i just checked that and its tight, no movement from months ago. My money would probably be on the focuser or secondary. What about tube flexure (twist from one part of the sky to the other?)

Originally Posted by alocky

There has to be some differential movement between the guiding and imaging chips if your guiding graphs are correctly indicating sub-pixel guiding. What rate are the corrections being applied at? Are the guide graphs sooth?
Cheers,
Andrew.

Hi Andrew,

Guiding graphs are good. there cant be any differential flexure between the chips as im using the internal guide chip on the stl (both in the camera head), not an external guide scope. Unless your of the opinion there can be differential flexure in there?

Originally Posted by gregbradley

Yes that is a possibility too. If your mount is unbalanced or it shifts in balance at different angles (do you have a piggybacked scope?) or you camera filter if sticking out at an odd angle. Dragging cables.

See if you can check the balance of your rig at those angles you know you get elongated stars. It may be way off even if balanced when horizontal.

I always balance my scope at a typical imaging angle not horizontal which of course you never image at.

Greg.

I will reballance at the low angles and do it again to check. my guide graph indicates there is no problem with guiding at these altitudes (40 deg) though. There are no cables to get snagged on, everything is through the mount and the mount is free to move where ever it wants.

thankyou all, I will work on these suggestions and see how it goes.

Josh