Celestron Field Flattener Follow-Up

This is a follow-up of a previous post.

I was able to image the other night with the short nosepiece. Recall that my goal was to get the system to match the presumed optimal f/6.3. It was f/6.0 with a long nosepiece/adapter in place, and by switching to a simpler nosepiece it allowed me to trim about 8mm off the FR/CCD separation. While the image is not very good, it's good enough to allow astrometry.net to plate solve it and calculate the pixel scale.

Here's the image:

NGC 7625 (small galaxy at center)

This was based on 30 minutes total exposure for each RGB channel, under near-urban sky. It could be a lot better, but sometimes one must take what the sky and gear gives.

The pixel scale is reported to be 1.51 arcseconds per pixel. This is really close to the value of 1.50 that corresponds to a focal ratio of 6.3--the error is only about 2/3 of one percent.