M51 (and NGC 5195) Using NIR, sYel, sV + H

May-Jun 2012 + Jan-Feb 2013

M 51 is one of the most viewed and photographed of all of the Messier objects. Its spiral arms are easily visible in a 15" or larger scope. With careful observation the bridge between M51 and nearby NGC 5195 is visible.

The following images were taking with my Narrowband for Stars technique. This image is shown full resolution of 2"/pixel.

click here for a wider crop. This shows some other galaxies in the same part of the sky.

Combining Hydrogen

I took some hydrogen images using my narrowband 3nm filter last year while I was testing LRGB. I managed to get a full projects worth of H before I ran out of time.

For the following I combined a fully processed H image two different ways to see which one was more appealing. Since they both seem equivalent to me I present them both. I used PixInsight's color saturation tool to enhance any strongly red areas.

Max

Additive

Again with the Ha20 filter that will be in my new camera I will be capturing Ha{+N II} directly so this technique will not apply in the future.

Processing Details

Filter	Exposures
Strömgren sV	1200s x18
Strömgren sYel	1200s x 20
NIR	900s x 28

Hydrogen (3nm)	900 x 28

I processed the image in two steps. First I formed the NIR-sYel-sV image above as described in the NB4Stars page by combining the raw images to form an RGB image. Each channel was pre-stretched using the masked stretch script (to minimize the stars). I then formed an RGB image using the following expressions in PixInsight PixelMath.

Red = "NIR*.33+sYel*.25";

Green = "sYel";

Blue = "sV*1.2+sYel*.1";

As a final processing step I had to cut back the blue using Curves so I am still getting too much blue in the final image.

For the H image I created a full H image. At several stages I aggressively used Morphological Transformation to reduce the intensive of all of the stars. By doing this only the H in M51 will contribute to the final image. I then combined this image with the NIR-sYel-sV. Since I will not be using this technique in the future I will spare you the details.

Area Map of M51

Area Map
midnight May 9

Individual Images

These are the raw images used to construct the composite above. The Hydrogen image is fully processed. The other images only have a simple stretch.

NIR	SYel
sV	Hydrogen (processed further than the other images)

Copyrights for Photos

Except as noted, all work on this site by Robert J. Hawley is licensed 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.