Celestial hemisphere:  Northern  ·  Constellation: Ursa Major (UMa)  ·  Contains:  Bode's galaxy  ·  Bode's nebulae  ·  M 81  ·  NGC 3031
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M81 - A Backyard Bode's Galaxy, wadeh237
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M81 - A Backyard Bode's Galaxy

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M81 - A Backyard Bode's Galaxy, wadeh237
Powered byPixInsight

M81 - A Backyard Bode's Galaxy

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Description

This is M81. Bode's Galaxy.

We had a stretch of clear nights in early March, 2019 that happened to coincide with very little moonlight, so I wanted to go for a redo of this object. I imaged it last spring from Pixieland Star Party, but the conditions were quite poor. You can find that image in my gallery to see the challenges I faced and the result.

This one was taken over 3 nights, from March 2 through March 4, 2019.

I experimented with a few new techniques in PixInsight, most notably the MureDenoise script. This script is intended to use your camera's measured noise characteristics to apply different kind of noise rejection as the very first processing step after integration. Other noise rejection algorithms are essentially specialized blurring algorithms that, if used in the linear state, can leave artifacts that are very difficult to address in later processing. With MureDenoise, I was able to pretty effectively tame the low level background noise in my camera. I am thoroughly delighted with it. It gave me a very good foundation upon which to do the rest of the processing.

The details for this image are as follows:

Telescope: Celestron EdgeHD 8 @ F/7

Camera: ASI1600MM-cool with 1.25" Astrodon GenII RGB filters

Mount: Astro-Physics AP1100GTO-CP4

Guiding: Starlight Xpress Ultrastar with Teleskop-Express Thin OAG

Capture Software: SGP with PHD2

Processing Software: PixInsight

Capture Details: 68x180r, 72x180g, 67x180b @ Gain 76 & Offset 40

As some additional notes, this is still an object that gives me some trouble with colors. Even though I use PhotometricColorCalibration and get great fit in the graphs, I always get a greenish tint to the galaxy core. Also, I find very few areas of clean, blue color. I've seen other images with substantial blue in the galaxy arms, but I just don't see it in this galaxy.

And finally, the two brightest stars in this image have some tragic halos that are partly a characteristic of the cover glass on the Panasonic sensor in the ASI1600. It does not have an anti-reflective coating and will present a grid of reflections around bright stars. If I push the luminance on this image, I can clearly see the effect. As it happens, I've not pushed the luminance anywhere near as far as it could go, so there's no problem there. But pushing for sufficient color saturation made the issue much more noticeable in the chrominance layer. I'm continuing to consider the best processing fix for it. If you have ideas, let me know.

Thanks,

-Wade

Comments

Revisions

  • M81 - A Backyard Bode's Galaxy, wadeh237
    Original
  • Final
    M81 - A Backyard Bode's Galaxy, wadeh237
    B

B

Description: This is a reprocessed version of my M81 data, taken in March 2019.

I started with the original channel masters and used MureDenoise to create updated masters. The new, denoised masters make it possible to stretch more aggressively. I re-cropped the image into an orientation that I prefer. I paid more attention to the brightest stars, using a variation of Adam Block's Star De-emphasis (see https://www.adamblockstudios.com/articles/star_demph).

And finally, I changed my approach to color balance. The original color mapping was strongly influenced by the data itself, along with PhotometricColorCalibration. That left the data with more of a yellow and green cast that I wasn't happy with. In reprocessing the data, I worked with the blue/yellow balance to get the outer arms more blue, and the core more yellow.

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M81 - A Backyard Bode's Galaxy, wadeh237