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M33 - 2011 Retake

Nov-Dec 2011

Originally I thought that I could not take color images since my observatory is located in the city and subject to both local and regional light pollution.  At AIC 2011 Don Goldman convinced me that it was possible.  The city lights are still a problem.  The luminance exposure is limited to 420 seconds.  Even at that short exposure there is a significant gradient to remove with DBE.  While longer exposures are possible with the color filters I have limited them to 300 secs.  The Blue filter had a significant gradient.  H alpha exposures were set at my standard 900 seconds.

For More infomation

click on the images below for a larger image

Color Image

LRGB Image

The image uses the Luminance filter to describe the brightness of the image.  The Red, Green, and Blue filters are combined  to form a RGB image.  While this image looks like the final, it is of lower quality.  After processing the RGB image is used as the Chrominance (color) to supply color to the Luminance Image.  This results in the image above.

M33 Color Enchanced with H alpha

LRGB Image enhanced with H Alpha

In this image the Red channel is enhanced by adding a portion of the H alpha signal.  See below for more details.

Creating the Image

Hydrogen Alpha
RGB Image
The RGB image was formed by combining images taken with each color filter using HDR techniques.  I used HDR because the bright stars were saturating in my test shots.  Since I want well colored stars, I shot short duration exposures and then combined them with HDR Composition.

There are really not enough of the long exposure images.  Originally I was taking 600 second shots, but after more study I decided that 300 sec shots would be enough.  Unfortunately I ran out of time (and good weather) as M33 is not setting into my trees rather early.





300 15

Hydrogen Alpha Image

The H alpha image is a rather straightforward combination of 40 900 second exposures.  Since I was also testing the effects of the moon some of the exposures had gradient due to being shot too close to the moon. 

For the LRGBH image I used the technique described by Harry's Astro Shed. In my case I got better results by using the finished images instead of working the linear image.  Harry's technique is to create a scaled intermediate of the Ha image and then combine that image to form the final "Rh" image.
Luminance Image

The Luminance was 43 exposures of 420 seconds each. Since I do not have a rotator I DBE'd each sub exposure to remove the gradient caused by local light pollution.  The result was a fairly clean image

All of these images were processed using the new PixInsight 1.7 Gradient, HDRMultiScaleTransform, and MultiscaleMedianTranform functions

Active Map

Animated Map of M33

Last Year's Image

Last year M33 was one of the first astrophotography projects I attempted at the observatory.  Aside from this being a color project and the 2010 project being grayscale, this time I used the FSQ 106 and have the mount better tuned for good tracking.

Copyrights for Photos

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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.