This image is part of a collaboration with Andrew (Professor2112) in which we agreed to combine LRGB data from my Esprit 100ED refractor with H-alpha data from his TS-Optics Photoline 130 mm refractor in order to get longer integration time on M81 and M82.  Andrew was eager to process M82 and its H alpha jets, so I selected M81 and NGC 3077 as my part of the image.  Andrew is not done processing M82, but we can look forward to seeing it next week.  Splitting up the field of view is one way to avoid posting two highly similar images to our galleries for a collaboration, like we did for IC 342 last fall.  I do wonder if some people will question why I would crop M82 out of the image, though.   The full sensor view from the Esprit would have required some clicking and zooming in to appreciate the H-alpha details, so perhaps it's better to post the results as two cropped close-ups.

This image has a total integration time of about 48.6 hours as follows:
23.3 hours of H-alpha (600 s subs, Chroma 8 nm H-alpha, ZWO ASI2600MM Pro)
14.0 hours of luminance (300s subs, Baader L and Chroma L filters mixed, QHY 268M PH in Mode 3, Gain 14)
11.3 hours of RGB (150s subs, Baader RGB and Chroma RGB filters mixed, QHY 268M PH in Mode 1, Gain 56)

The LRGB data were captured from my backyard in Pittstown, NY under Bortle 4+ skies starting on Oct. 22, 2022 with my old (2012) Baader LRGB filter set.  The last subs were captured on 2/18/2023 using the new Chroma filter set I got in December 2022.  Processing the stacks with two different filter sets and two sets of flats was not fun, but it worked out.  There was a run of 52 consecutive nights of poor weather or moonlight right in the middle of the project where I couldn’t collect a single sub, so it was a relief to get some clear skies within the last week or two.

The H-alpha subs were collected from Springfield, Mass. under Bortle 7 skies and Torrington, CT under Bortle 4 skies over the same time frame using Andrew’s scope and Chroma 8 nm H-alpha filter.

I platesolved the 14-hour luminance stack in the program ASTAP, which reported a limiting magnitude of 21.9, so the luminance channel goes quite deep for a little old 4” refractor.  Besides M81 and NGC 3077, other galaxies swimming around behind the IFN include LEDA 28731 (faint blob near the bright orange star, left of M81), UGC 5302 (or PGC 28563, lower left corner of image), and MCG+12-10-007 (directly underneath M81).   The faint pair of galaxies between M81 and UGC 5302 are designated 2MASX J09551788+6837072 and 2MASX J09553415+6837063.  At full resolution, you’ll see many distant backround galaxies lurking behind the dust.

Here are a few words about processing.  The goal here was to bring out as much background dust as possible without overstretching M81 or introducing too much noise in the background.  Starnet++ v2 was used to remove stars to avoid overstretching them.  Topaz Denoise AI was used to tame the noise levels in the sky background, but with the AI sharpening set to 0.  I just don’t want to deal with the “fake details” issue.  After reassembling the stars and the starless image, I applied deconvolution and multiresolution sharpening to M81 using MLUnsold ImagesPlus.  Most of the remaining LRGBH processing was done in GIMP or Siril.  Removing gradients from light pollution was more difficult than many of my previous images, mostly because M81 does not rise as high in the sky at my location as some of my other recent targets.  Seeing ranged from good to terrible during the many nights of data acquisition.  I wish I could have shot all the subs in late summer / fall when the seeing was good around here, but the project carried over into the blustery winter months.