Wikipedia describes M74 as “the most difficult Messier object for amateur astronomers to observe“ because of its low surface brightness. Indeed, the first time I set out to image it three years ago (
https://www.astrobin.com/b388of, 5 hours of integration from a Bortle 3 site) I was very underwhelmed by both the signal-to-noise ratio and the lack of detail. When I approached this target again this month, and from my home backyard, I did so with respect and as an experiment, thinking that I’d just switch to something else if it turns out to be a disappointment. After the first night of data collection, the integration showed potential. So I continued in RGB and H-alpha until I had about 5 hours of data per each filter.
Broadband imaging from under heavy light pollution requires patience to integrate for longer time, and some ingenuity to model the background. From my backyard, I usually end up getting some radial gradients, different for each filter. This image was no exception. I corrected the differences by trying to match the large-scale gradients among colors (an approach that’s possible for this field, where there’s no physical reason for large-scale differences among colors), and then using a more traditional DBE.
Even so, at roughly 20 hours of total integration the image had good detail but lacked “punch”. I then had the opportunity to use a dark(er) site for a few hours, so I added about 3 hours of luminance data, unfortunately collected in generally bad seeing. Blended with the luminance component extracted from the RGB data, this added depth without sacrificing too much detail.
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