APPM Image Scale Question and Suggestions


Hi everyone.

I have used APPM successfully with my Mach2 and 130mm Starfire GTX. I am now trying to build a model for my 1100 with a CFF 300 on it.  I have some specific questions about image scale. I'm using USNO A2.0.

The camera is a ASI1600MC-Cool with a 0.67 focal reducer on a 300mm f/15 Cassegrain. I calculate unbinned image scale at just under 0.26, which is of course pretty small. I binned 2x2. My initial run was not successful -- many failures, often reported as due to potential image scale issues. Later, using the image-link-test solve capabilities, I was able to get a couple of the earlier images to solve, but the estimated image scale in those calculations was reported just over 1.0. When I re-ran the image-link-test solving with that 1.0 entered for image scale I got about half the images to solve easily.

Question #1: Is this inconsistency because of the 2x2 binning? Does the plate-solve results in the Image-Link-Test display estimated unbinned or binned image scale?  The math works: 4 x 0.26 is about what was reported. 

Question #2: Just to confirm, then, that when I enter X-scale and Y-scale factors in the platesolve setup, I should enter the unbinned values, right (0.26)? The software will then adjust, I assume, for the binning.

Question #3:  What options should I play with to reduce the potential for failed solutions due to image scale issues.  How high can I set (realistically) the Image Scale Tolerance?  Is 50% too high?  100%?  I also assume it would be helpful to set Catalog Expansion to a higher value, maybe to the max at 0.8.  I'n not trying to get fast solutions, just more solutions.

Question #4: Any other suggestions for running APPM with such a small image scale?  I was worried about getting enough stars so I increased the exposure time on the camera (from 5 to 15) and reduced the sigma above mean (from 4 to 3). Anything else?



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