[pmrid (Peter)]

I have just done a comparison between the results from a PoleMaster (with SharpCap) and ASiair Plus.

What led me to this was noticing that after a 4 hour imaging run last night (having done an ASiair PA at the start), when the scope returned to the CWD home position, it was actually pointing a noticeable amount to the left(east).

Trying to figure out the reason was not easy. For me anyway.

I was using a SharpStar 94EDPH scope with a .8 reducer/flattener and an ASI120MM Mini guider on a 120mm ZWO scope - all sitting on a HEQ5 Pro.

Throughout last night’s session the guiding was sub-arcsec according to ASiair.

So tonight, I’ve started with a PoleMaster SharpCap PA. It told me that the scope was pointing a good 8 arc-minutes low. So I decided to adjust the height accordingly and followed with an ASiair PA which told me I was out the other way.

So the answer seems to me to be that there is a non-orthogonal error and the scope, sitting in the mount’s saddle needs to be shimmed up a bit.

Any other ideas anyone?