astrodeb@charter.net wrote:

Has anybody tried the Drift Alignment method to accurately polar align a GEM mount? I found this method at www.darksyimages.com/gpolar.html

The Ealing at SPOC is a GEM and we aligned it with the drift alignment method (same for the scope at the original SPOC and for the Big Scope at the current SPOC. Drift alignment can be quite accurate and should get you to within a few arc minutes of the pole but is also very time consuming if done right. Unfortunately, drift alignment does not take into account mechanical problems in the mount and drive system but you'd need to buy special software to take care of those problems.

I had some field rotation in my images last time...

I would think your alignment would have to be off by quite a bit for that to happen.

My other question is how long does this method take to get an accurate polar alignment?

Well, if you were going to put up a permanent installation I'd say several hours. But if you're going portable I'd think you could get it "close enough" in less than an hour. There is one other option that I've had good luck with, namely a nifty device called a Tuthill Precision Polar Alignment Scope. Quick and accurate but a search of the web just now only came up with dead links and links to pictures from users (like http://www.rphotoz.com/astrophoto/mi250alts.html ). Apparently they stopped being made when the creator died. I do have one you could borrow next time you're up this way. Patrick