CCD Drift Polar Alignment - It's Worth the Time

I purchased a CI-700 GEM for imaging a while back, installed it on a permanent pier, and performed a relatively quick polar alignment using the polar scope. I figured the autoguider with my SXV-H9 would guide out any error. The best I could tell the peak to peak guiding error was about 3 to 4 arcseconds plus some field rotation over a several hour series of images. Often stars had a lump on one side, which I now attribute N or S correction always being one direction due to poor polar alignment.

So the other night I decided to perform a CCD drift polar alignment, based loosely on the instructions in the HELP menu of MaximDL. After about 2 hours of fine adjustments the polar alignment was very good. I set up a guide error chart in MaximDL and clicked off actual tracking. Over a period of about 8 minutes the E/W periodic error (PE) was about a 10 arcseconds peak to peak. The N/S error was within 3 arcseconds. With autoguiding on, the total peak to peak tracking error in N/S or E/W appears to be less than 2 arcseconds.

Images the last few nights, since the CCD drift alignment, appear to have considerably better stars (no more lumps). I've attached a picture cropped and stitched from "before" and "after" images, 1-1/2 hour (9 x 10 minute) and enlarged x3.

The bottom line. Don't be like me and get so excited about getting your hardware together and wanting to produce images that you fail to perform an accurate CCD drift alignment. That and good balancing go a long way towards improving your tracking and your images.

Thanks
Steven Jindra

Attached Image:

Hear, hear Steven!! I totally agree. I messed up a drift alignment at a dark site last week that ruined an evening of perfect conditions for imaging - totally clear, totally dark rural skies, excellent seeing. I spent a later niht studying exactly where the south Celestial Pole is in relation to other easily spotted stars.

That way I can get a quick alignment that enables a fine tune.

Another idea I had was to spend some time getting a superb drift alignment. Then attaching a laser to the mount.

Then I adjust the laser to land on the pole.

Next time I can simply turn on the laser and adjust it very quickly.

Greg.

Hi Steven,

Given that it took you two hours, I presume there was no software assist involved in this method?

I've been thinking about trying a drift alignment myself after last night - I set up and tear down every session, and I have to set up on my lawn in order to see Polaris. Last night was not pleasant, as the lawn was pretty mushy and muddy after some rain. It's made me seriously consider setting up on my patio (where I can't see Polaris) and attempting a drift alignment. Perhaps with some help from PoleAlignMax.

Eric

Well done Steven on your polar alignment. Remember though, it's just one step out of many to produce a graet image. Good focus, flat fields, dark frames, color balance, the right exposure, it goes on and on. Not one step can be shortcutted or it will show in your image. Most important is HAVE FUN!!!