Celestron Edge HD 1100 Second Light
NGC 6905 with EdgeHD 1100 and STL11K camera
This may seem a target poorly suited to the FOV but there's a reason I chose this. There is a fairly dense starfield so you can evaluate star shape and size
all over the field. There is also a very small (1.7 arc min) Mag 12 target in the middle to see resolution in a small nebula.

The first image below is the entire image.

The second image "4CC" (Four Corners and Center) shows the center of the field and the extreme four corners where coma and astigmatism will be the
worst.  This is a very tough test of an image. The 4CC image is at 1:1 scale i.e. one pixel on the monitor is one pixel on the camera.

The third image shows where the "4CC" images lie in the full frame.

I can see minimal elongation in the upper left and lower right frames of the 4CC image but you have to really zoom in on the extreme corners to even get a
hint of that.

Note that this image was taken under a 13 day moon from within about 10 miles of the center of the 10th largest city in the US.
NGC 6905
1 hour each L, R, G, B

Right click on image for full image (2.9Mb)
Location of the sub panels in "4CC"
(Four corners and center)
CCDInspector analysis of the subframes. Note that to get a quick look at what images I could get with this new scope I ran all night and the last subs were
at Alts in the teens and Air Mass up to 4.14 (and that happened to be B data).