Here is my test bench (messy to add authenticity):
For testing this scope I used my new coated 12.5” flat. The flat holder and stand were custom made by Mark at Astrogoods. Adjustment bolts on the back of the flat holder make it a snap to fine tune alignment of the flat with the scope! The screen/LED holder in the focuser (made by CN member Moshen) holds the 3mm RGB 4-lead LED, which is connected to the home brew switch box (on the white board) which has a separate dimmer control for each color. There’s a separate screen/LED holder for the white LED. The power supply is my bench supply, but a cheap wall wart works just as well. My old World Books temporarily taken out of retirement hold the scope, and a Nikon D40 with a 18-55mm lens (set at 55mm) was used to take the pics. Paint.net was used to package the images.
Here are my results (each row shows inside of focus, at focus, outside of focus images):
My interpretation of the pics is that the scope is moderately overcorrected in blue, with lesser overcorrection in green, and slightly undercorrection in red. Based on that, my guess is that best correction is in between in green and red, in the yellow range. Overall correction seems to be pretty good for a 6” f/6. The in-focus pics show a zone in the center of the objective, and at the edge at 1 o’clock and 6 o’clock. I don't see any turned edge. Any ideas what caused the zones at 1 o’clock and 6 o’clock?
During use, I don’t notice CA at low to moderate magnification, but it is there at high magnification, for example when using my XW 3.5 EP. Overall I’m satisfied with the scope, considering the aperture and short focal length.
I'm still a beginner in DPAC testing and have a great deal still to learn, so your comments and recommendations are especially welcome!
Thanks,
Howard