X2D Astrophotography: Shutter control app to Dither between frames

[grotte]

After trying my rig consisting of X1DII with Tele-ApoTessar f/8 500mm (with and without Mutar 2x converter) and Skyguider Pro, I think the unsolvable problem is the severe chromatic aberration of this lens. The aberration is not visible in terrestrial images, and not even in solar, but is quite prominent with the stars. Even though I can correct magenta halos in Phocus, the dust cloud color then shifts too. For example here is the uncorrected image of the center of the Pleiades cluster and superimposed extreme edges of the frame. 100% crop, ISO1600 f/8, 5min exposure. I am surprised how well behaved tracking was, and yet the result is frustrating. Is it time to invest in a Tackahashi?