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Thanks all.
I have given up chasing FWHM with this scope - fruitless exercise, since the refocus adjustments are so darned minute. I honestly almost touch the focuser knobs in or out - microscopic movements near prime focus! It really needs a dual speed knob - might see if the Vixen dual rate adapter can be converted.
I am running a focuser image routine in MaxIM - 20 second exposures seem the best for it. And then doing it BY EYE. Yeah, no figures, no Bahtinov (though tried the Bahtinov - it's still chasing the tail in many ways).
In the non-stacked lightly stretched images, the double star that Ray is discussing is in fact distinctly 2 stars. Stack and stretch, and they merge a little. I am also using the PI BatchPreProcess routine for stacking, so the light frame calibration is not exacting (as the disclaimer also says). DSS yields a similarish result though anyway!
Yes, I have decided to go with a robotic focuser of some description - have not decided fullly which one as yet, but most likely the Sharpsky.
The issues I had with the colour shots most assuredly were related to the faulty SXVR-M25C - it LOOKED like a collimation issue, but there is tilt in the image (NOT apparent with the SBIG - perfect across the field in Lum and Ha), not fully "filled" pixels, and NOT debayering corrctly (I can fully see red, green and white in a zoomed star image - the blue channel has gone to poop). The SXVR also failed cooling the other night. The issues began about 8 months ago, and I have been in contact with Terry since day 1 - initially a massive drop in resolution between frames, then the graininess despite the cooling working, and then the cooling failing almost. I sent it back yesterday to Terry to look at.
So, in summary, I think the scope is fine. Maybe a VERY small miscollimation (the star test shows an EXTREMELLY small asymmetry, but I can notice it). Focusing is the issue. Additionally, I need to get off my butt and do measurements for both the Sharpsky, as well as finish the dimensions for the light cone I am having made for it (I am getting a fair bit of vignetting, since the 4" drawtube ABRUPTLY steps down to the 2" adapter - I will have a cone made with rib baffling to eliminate a lot of this).
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