I have the ES ED127 F7.5 refractor. I'm trying to figure out if my focuser is out of alignment. I used a Cheshire and know my optics are perfectly collimated. My images are very sharp corner to corner. I checked CCD Inspector and the interesting thing is, I have an ES Focal reducer Field Flattener. CCD Inspector shows a 34 degree curve in the image but no tilt. I thought a field flattener takes out this curve? Anyway, my images look sharp so I'm not complaining. But, looking at this image of my Master flat, the circles are not centered, I cant figure that out. I put a laser collimator and the dot on the wall didn't move when I rotated it?? So, why the offset circles?? Any ideas, thx.
**NOTE The checkered pattern in the image is just a png to tif conversion issue, not present in the Master Flat