[Andrew C]

I need some advice.

I have a well used CG5 goto eq mount which I am using with a 6” Newtonian Celestron and Watec video camera for deep sky stuff. When taking reasonably long exposures (say over 1 minute) the images drift noticeably. Normally I would put this down to poor polar alignment, but I am reasonably confident that I am getting this right to within 5 arcmin or better each time. There is no facility on the mount for adjusting the sidereal tracking rate so I can only assume that that is OK. I have gone to some pains to check and shim the OTA to align it with the mount polar /RA axis.

One other area that I wonder about is the indexing when setting up the mount at the beginning of the session. Given that the index arrows are on a shaft of about 70mm diameter, a misalignment error of 0.5mm on indexing the dec axis (about as good as I can be sure of in the dark) would represent about a 50 arcmin wobble when rotating the scope on its RA axis around the SCP! One can polar align the scope very accurately in a single position, but this level of indexing error will overwhelm and negate that effort.

What I am wondering is: Does drift alignment cancel/overcome this error and should I be concentrating my efforts on practising that process, or will the dec indexing error remain to affect drift alignment as well (which would mean I will have to get the dec indexing right by repeated trial and error)?

Thanks, Andrew