M51 with a cheap 4.5" Newtonian

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Lyle Aldridge Contributing Member • Posts: 998
M51 with a cheap 4.5" Newtonian
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Our sky in Tucson has been pretty cruddy recently, with clouds almost every night, and more recently, with high winds that have filled the air with dust. Night before last, however, the clouds had blown aside, and I decided to ignore the dust and wind to see what I could capture with a cheap, thrift-shop Newtonian I'd been waiting for a chance to use on a deep sky object. So here is the resulting capture of the spiral galaxy, Messier 51:

44x120sec, unguided, Canon T2i @ 1600 & 3200 ISO, DSS stack, GIMP 2.9 post

This scope was modified by hack saw, removing about 2" from the mirror end. It's using a 900mm f/8 mirror, so it shows a lot less coma than we see from faster reflectors. What I found objectionable was confined to about the outer 10-15% of the frame, and fell to my "crop-tool coma corrector" in Gimp 2.9. Even in the polar region, my LXD mount's unguided tracking leaves a bit to be desired, but it looks to me like the $12 scope is out-performing both my mount and my camera. There is a slight hot spot to lower right that my flats didn't completely eliminate, but I'm planning see whether a few more will remedy that. I think its location in the frame probably means I should make some adjustments to the location of the secondary mirror, but if flats will do the trick, I may ignore that for later.

As an aside, some may wonder about the mixed ISO settings. So do I. My T2i is cursed with some formidable correlated or "walking" noise at 1600 ISO and below. For reasons that are a mystery to me, I've recently discovered that the noise seems reduced when I mix a substantial number of higher-ISO frames into the DSS stack. I can't be sure whether there's really a causal connection, but would be interested if anyone here happens to know why that might or might not be what's making the difference.

Canon EOS 550D (EOS Rebel T2i / EOS Kiss X4)
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