[g__day (Matthew)]

I've been driving at polar alignment for quite a while now on a permanently mounted scope on a pier. I have reached the point where I am wondering if its the optical design of a mid size SCT that is restricting me achieving better polar alignment than 1-2 arc minutes.

Basically I am wondering does mirror flop on an SCT restrict one from achieving < 10 arc second polar alignment - becuase what one sees and thinks is DEC drift is actually complex mirror flop.

I'd love to hear folks thoughts on the matter. I have run PEMPro polar align wizard night after night - for 20 - 30 minutes per axis and have drift recorded of under 2 arc secs per 30 minutes - in both RA and DEC. But when I do a 50 star MaxPoint sky model it tells me I am respectively 1 and 2 arc minutes off the SCP.

I ponder is polar alignment error I am seeing modelled actually the result of mirror flop?

Looking at 6 and 8 minute unguided shots at 2.3 metre focal length (a C9.25") I see 1 mm star trails on 1 mm stars - so say a few arc seconds drift - not sure if its RA or DEC.

To prevent the mount tracking fast - with the mount set in polar aligned mode - I have to do a 3 star alignment to get tracking to look right within say 10 arc seconds an hour.

PEMPro also reports tracking PE to be within +/- 2.111 arc seconds raw - so this is kinda superb. So I ponder is it the mount is great but mirror shift / flop on the primary making it impossible for me to get better alignment?

What are your thoughts and how good a polar alignment can you achieve drift aligning with a SCT?