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Gary,
Huge thanks for your replies. I know the SkySensor2000-PC is meant to calculate and handle refraction - its old fashioned but smart.
I ponder is there any polar misalignment or mirror shift that can manifest solely as an error in RA rate rather than DEC? This stumps me a bit - the shift is always along the RA axis - which to me reads like a tiny tracking rate error (like its one part in a thousand faster than it should be).
I track a star for 30 minutes and see maybe a 1-2 pixel drift in DEC (so say an 1-3 arc seconds or 25% of a star diameter out of position) but in RA it is likely to be 4 star diameters out of position in RA.
I am trying now to see if I shoot a series of 30 * 10 second shots - spaced a minute apart over half an hour how much drift I see in RA and DEC and determining:
1. If I change the elevation of the mount slightly - does it improve or worsen
2. Is the error growing, shrinking or consistent with elevation.
Data empowers one to diagnose the source of the problem I guess!
Matt
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