It's official! My first mosaic of a starfield. I enjoyed a widefield view of the iconic double cluster using my
SLR camera lens recently, albeit at a low imaging scale, leading to severe under sampling. In my SCT at f3.3 I can't squeeze these into the FOV, so decided a higher resolution mosaic was in order. I've used Microsoft ICE to create
lunar mosaics in the past.
Han Klein's excellent (and free)
ASTAP software enables image stitching using internal astrometric solving. After calibrating, aligning and stacking my LRGB subs for each cluster, the software got to work creating a 1x2 mosaic - double the fun!
Talking of calibration, this has been so hit and miss over the past year, that I spent the evening trying to get to grips with this. By calculating the minimum and maximum ADU of my DSI III Pro camera, I was able to arrive at an optimum 16,500 ADU for my flat frames. This worked flawlessly removing the severe vignetting and some dust donuts in my LRG filters; blue needed a sightly higher ADU setting.
Armed with 'clean stacks', I was excited to start processing these in Startools. Apart from a strange artifact at the image join, which I have removed, this was straightforward, and I'm quite pleased with the result. Both clusters fit nicely, but I would have liked a larger FOV and will have to do a 2x2 or even 2x3 mosaic next time. All good preparation for a planned mosaic of the Andromeda galaxy, which I have worked out will need at least 2x6 frames!
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