[Joshua Bunn (Joshua)]

Originally Posted by TanjaC

Hi All,

Coma
- I have an Officina Stellare reducer / flattener fitted. Seeing that without changing camera orientation - imaging N yields round stars in the corners, and keeping same setup - immediately slewing and imaging S makes it appear like field rotation

This would indicate that something is shifting. It could be the focuser drawtube isn't up to tension. Also, how is your camera attached to the focuser? If its a push fit with a nosepiece, its certainly going to cause some problems like your seeing as you move to different parts of the sky. Threaded adapters or bolt up adapters will stop any parts shifting as you move the scope around.

Originally Posted by TanjaC

Balance.
- I know my balance is a little off. It's balanced horizontally in Dec (balanced in RA), but not vertically in Dec.

Try adding some weight to the other side of the tube to counter thatever is making the scope rotate when pointing at the zenith.

Originally Posted by TanjaC

Also another question, should the OTA be slightly off balance in RA to give the motors something to work against? If so which side?

If you think it may help you mount, when imaging on the east side of the meridian, slightly apply more counterweight to the counterweight shaft by sliding the weights down the shaft just a little. On the west side of the meridian, raise the weights up the counterweight shaft so the OTA end has slightly more force. What you are trying to achieve is for the RA worm to be pushing on the gear.

Originally Posted by TanjaC

Help appreciated. What can I try to fix this
Thanks

I would really try to eliminate any non orthogonality of the camera to the light path first. So try to make everything square and secure. You may need to use some shims here. I assume your scope is well collimated?

Peters idea of using CCDIns is also a great recommendation.

Josh