CCD Imaging Primer
	Imaging Made Easy and Fun!

When doing multiple, short exposures, it is not unusual to spend half an hour or more on a single object. Chances are that the object will drift gradually up/down and maybe even right/left on the frame.

I compensate for this when I notice that it has moved too far (I keep a close watch, noting the positions of various stars around the edges of the frame) by briefly pushing the N,S,E,W buttons on the LX200 keypad with its speed set to "Center" (nothing faster than this or you will move the telescope way too far!). On my system S moves the object up, N down, W left, and E right.

Experiment with moving the object in this fashion, re-imaging (say a quick 5 or 10 second exposure) after each move. Once you're proficient in doing this, you can keep the object centered in the frame over long periods of time so that your final, combined image won't get cropped too much.

Here, the current image in the sequence (#15) is put on top of the first image of the sequence so that field drift can be monitored (MaxIm automatically dumps the latest sequence image into the window shown here on top.)

By comparing the two circled stars, you can see that the field has drifted towards the top by a few pixels. Also note the star at bottom (arrowed) that has popped onto the frame as a result of drift.

Compare the two stars at middle left in the frames (arrowed). In right (latest) frame, this star is closer to the edge: the field is drifting very slightly to the left.

Of course, there are fancier (i.e. more complicated) ways of doing this, but I find this simple technique to be quite efficacious.