Hi Greg,

I am wondering if you tried or would try to solve either image outside of the ACP environment, for example using MaxIm's plate solving. You can set up MaxIm's parameters to match those of ACP. It would be helpful to know if MaxIm also takes an hour.

It's reasonable to see 30000 image stars in your wide field 20 minute exposure. The GSC has about 400 stars per square degree averaged over the whole sky. For your .55 square degree image there would on average be about 200 stars, but you're looking deep into the MW, so finding 700 stars is probably right, too. It's not surprising that the solution times were identical, since ACP found the same 701 stars both times. It is however hard to imaging what would cause it to take an hour, especially since the pointing image immediately before took only a couple of seconds with 590 catalog stars. Binning 4, however, not binning 1.

Is your camera a color "one-shot" CCD? If so, in MaxIm, if it still takes a long time to solve at binning 1, do a bin 2x2 (Edit menu I think - I'm not looking at MaxIm right now) and then see if it solves faster.

I'm still thinking about this, too. It might be helpful to know if this problem exists at some other nearby place in the sky, still in the MW, and maybe also somewhere not in the MW.

Is this the first time you've encountered this problem?