Although this is probably obvious to most experienced astrophotographers, I recently experienced firsthand the value of dark skies. After a solid month of rainy weather (highly unusual here in the western desert of North America, but badly needed), I finally got a clear night (but one with a lot of Moon). This was first light for me with Nebulosity 4 controlling the acquisition, which proved problematic. Image downloads froze a couple of times, and I assumed they were happening because Windows was running updates and slowing things down. Bad assumption. I left the session running and went to bed, but downloads froze again right after I did, so I didn't get very much data. I believe this is a bug in Nebulosity 4's option which allows the camera to be run on its own thread. Taking flats the next morning I had the problem again, and eliminated it by unchecking that option. This is probably better than last year's effort, but could have been much better with more data on a darker night.
The B image illustrates the importance of dark skies in galaxy imaging. 30 May had much more Moon than 28 May did, and had some high clouds too. As a result, although the B version has more than 4 times as much integration as the 28 May data (and includes the 28 May data in the stack, for a total of 59 300-s subs), it looks worse. The brighter sky background just killed it. To be fair, the processing was not identical; I just couldn't stretch it as aggressively.
Date: 28 May 2015
Subject: M101, Pinwheel Galaxy
Scope: Astrotech AT8IN
Filter: Baader Fringe Killer
Mount: CG-5 (Synta motors, PicGoto Simplificado)
Guiding: 9x50 Finder/Guider + DSI Ic + PHD 2.5.0 (Win 7 ASCOM)
Camera: DSI IIc no cooling (about 13 °C)
Acquisition: Nebulosity 4.0
Exposure: 14x300 s
Stacking: Neb 4.0.1, bad pixel map, bias included, 69 flats, histogram match, deBayer & square. Stacking 30-70%tile.
Processing: StarTools 1.3.5.289 Crop; Wipe: 80%; Develop: 80.11%; HDR
ptimize; Color:Cap green to yellow, Scientific 301%; Deconvolute 2.5 pix; Track 4.5 pix, smoothness 90%; Magic:Shrink 1 pix. Photoshop CC 2014 + Carboni Astronomy Tools Deep space nr; Healing brush; Astroframe.
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