Here's M31 a couple of more times, but this time from the Heritage Park Observatory. The AT80EDT is mounted on top of, and guided using the DSI through, the 10" LX200. Now we can make judgments about chromatic aberration (CA, the colored halos around bright objects) and field flatness.
Here's the first go:
Click for the full size and look in the four corners. You can see that the stars are streaks pointing away from the center of the image. That's the field curvature. The good news is the lack of CA--if it's there, I can't see it.
So I added a TeleVue field flattener in front of the camera. It's not designed specifically for this scope, but since it was the cheapest option by two-thirds, I figured I'd give it a try. It increases the focal length by 10%, so I get a slightly smaller field of view.
The corners still aren't perfect, but I'm pretty happy with the results.