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M 42 in HOS using HDR

December 2017
February 2018


The Orion Nebula is one of the most iconic deep sky objects.  It one of 3 or 4 Messier objects naked eye visible from here.  M42 has always been on my to do list.  Winters here are usually warm, but cloudy.  In past years I have used the limited time available for more obscure objects.  This year a small window of dark, clear sky presented itself in February. I decided to use the test shots from December and do a mad rush to complete this object in less than a week


NH O+2*S palatte

M42 is a object that cannot be adequately imaged in a single exposure.  Hence the use of High Dynamic Range or HDR.  With this process images of several exposures ( each 16 bit integer) are combined to form a single 64 bit floating point image.  This image is able to encode both the very bright and very dim.  Originally I was going to use just 60 second exposures for the Triangulum and 300 second exposures for the nebula.  The latter did well on M42, but did not capture the surrounding H alpha clouds.  Thus I had to add another round of 600 second exposures.

I really love ACP Expert.  Unfortunately ACP Expert adds a lot of overhead.  On my normal 900 sec images this extra time can be safely ignored.  If you are trying to shoot 60 60 sec images within 4 hours then it cannot.  Even with the 300 and 600 sec images I needed to eliminate any useful, but unnecessary operations if I was going to complete the project before the clouds returned.  Thus I shot the entire project directly with scripts in ACP.  The scripts eliminated plate solving and for the 60 second images eliminating RBI Flood (which is itself 2 minutes).  Doing these allowed me to capture > 15 images at 60 seconds and 300 seconds in H, O, and S.  I was only able to capture Hydrogen at 600 seconds, but that was enough to add depth to the gas clouds surrounding M42.

Annotated Image

The image is presented north up. 


Annotated Image of M42

Close up of M42

This is a half size zoom into the heart of M42/M43.  Clicking on this image will bring up a higher resolution version.


NH-OS2 Image of M52 and Bubble


Zoomable Image

The full size image is about 4096x4096.  The following will allow the reader to zoom into the image to explore it more closely.  I like this version since it places the nebula in the context of the surrounding Hydrogen clouds.

R=Hydrogen G=Oxygen B=Sulfur


Processing Details

Here are counts of the quality accepted frames that were used for the various filters.  Naturally more images were taken.  These represented the ones that made the cut.


60 300 600
Hydrogen
15
24 15
Oxygen
18
25
-
Sulfur
14
23
-


All images were processed by Pixinsight. 

Since Hydrogen is stronger than any of the other signals I increased the initial contribution of O and S by 25%.  They were combined with PixelMath

	Red = Hydrogen
Green = Oxygen * 1.25
Blue = Sulfur * 1.25

The resulting image was VERY noisy outside of the bright inner nebula.  The final result is a tribute to TGVDenoise.


Here are some other processing items of interest



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(c) 2018 Robert J Hawley.
Except as noted,all work on this site by Robert J. Hawley is copyrighted under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. This permits the non commercial use of the material on this site, either in whole or in part, in other works provided that I am credited for the work.

3/11/18