CCD polar alignment?

Does anyone have any experience with aligning a GEM (in this case an AP1200GTO) by using a CCD camera? I have done a drift alignment with a reticle eyepiece, and used Tpoint (neither of which agrees with the other). My understanding is that using a CCD camera can be very accurate. Will be using a C-14 at f/7 with an ST8E binned 3X3 in focus mode with Maxim 3+.

Interested in where to drift...did the drift alignment pointed at a dec +20 within 1 hour or meridian and then very low in the east. No drift that I could detect in 15 minutes but am getting some RA drift so might try this method.

Thanks,
Mike

Mike,

I permanently installed GEM last year.

Firest I used the polar alignment scope. Then I changed to CCD exposures. I increased focal length wit a 3x barlow lens. This brings out any tracking errors mor easy.

I took pictures starting from 1 min. to longer and longer. In between I corrected the alignment. I did it with trial and error. 50% chance to get the direction right is OK. Then keep this direction until there is no further improvement...

BTW: By doing it with real CCD exposures you are also correcting for the error of refraction in the atmosphere. Hence this method is even better than theoretically perfect north pole alignment.

The procedure took me one whole night, but I did not have to touch it since 15 months. My rest error over appr. 1 hour is only periodic error of worms.

CU
Tom
http://www.licha.de/AstroWeb 49° 13' 54" N

Mike,

You can get a great alignment with your ST-8 by first calibrating your mount to the camera then guide on a star that is approximately +20 dec and 1 hour of meridian. BUT, turn off your RA and Dec corrections in the software and log the corrections for a turn or two of the gear. Now save the log file and graph the RA and Dec corrections with a spreadsheet such as Excel. The graph will show you any slight drift because the data will rise or fall. Make corrections by moving the mount east or west until the graph shows no drift and you will only see periodic error. Then point to a star in the east and do it again. Any drift means the polar axis is too low or too high. Again make your adjustments until there is no rise or fall on the graph.

I hope this helps - Cal Sandfort