Pacman Two Ways

Good evening, and thank you once again for dropping by and reading my astronomy based ramblings.  In this entry, I'm looking at a pair of images of the same target, known as NGC 281, or better know as the Pacman Nebula.  This is a target which I have imaged previously, but the data taken for the former attempt was using a different camera, scope and probably even a different filter too.  You can read all about that effort from back in November 2018 here.
Interestingly, looking back on that blog entry, I see that it was right at the start of my Pixinsight journey and when I was using the Altair 183c Hypercam camera.  That camera (I still have it) is fan cooled as opposed to TEC cooled, and I was using 3 minutes exposures to create the image.  Even though it was fan cooled, I still managed to process it well enough to deal with any noise by the look of it.

Fast Forward to 2025

This time, I've tried again, but with upgrades.  Nearly every part of my imaging procedure has completely changed from back then.  I am more experienced though still very amateurish.  About the only part of the whole thing that is the same is the Skywatcher EQ6-R Pro mount.  I now use an Altair 26c TEC cooled CMOS camera, usually cooled to -3 degrees.  I have also introduced a quadband filter and upgraded the imaging telescope from an 80mm ED-R doublet to a 115mm Ascent APO.  Aside from the physical changes, since 2018 there have been big changes in my processing abilities as I get to learn more about PixInsight and some fantastic people create new scripts to ever expand the processing capabilities of the software.  Even introducing a quadband filter into the imaging train opens up a whole new world of imaging possibilities.

The Images

The use of the filter, some scripts and learning from online tutorials has meant that I can now produce images to a reasonable (but never perfect) standard in different colour palettes with only minor tweaks made to the processing workflows.  These new and improved workflows tend to work best on nebulae and so I decided to revisit NGC 281, around 7 years after I first imaged it.

Both the following images were created using exactly the same data set made up of:

• Approximately 3 hours of 98 sec lights exposures
• 30 Flat Frames
• 30 Dark Flat Frames
• 30 Dark Frames
• Stacked and processed in Pixinsight

NGC 281 Processed in the SOO colour palette.

NGC 281 Processed in the SHO colour palette.

What Should I Change Next?

These images I think, are a big improvement from the first attempt all those years ago.  Any time someone gets 'into' a hobby or interest, there aren't many people who don't strive for improvement.  Be it in sport, art, DIY, baking or whatever.  Exactly the same applies to astrophotography.  Recently I have been researching optimum cooling temperatures for my camera, and while it is capable of cooling to -35 below the ambient temperature, that's at the extreme.  Note that it is below ambient, and not a true -35 degrees.  It seems that the general consensus is to allow the sensor to be cooled down to -10 degrees for best performance.  Anything cooler and you're in the realms of diminishing gains.  Just cooling the sensor to -3 which is what I use at the moment, has made a massive change compared to the fan only cooled 183c camera I used in the past.

During processing, I use some scripts, two of which are Blur Exterminator and GraXpert.  While the former doesn't necessarily deal with image noise directly, (GraXpert is the intended script I used for denoising), it does contribute.  After running the scripts and zooming into the image after those particular steps, there is no doubt that they do a brilliant job at denoising.  But there is still an element of noise.  I always try and imagine my images printed in a large format, or even on a huge monitor display and think that if that ever did happen, there would still be an element of disappointment because of the noise levels.

Temperatures of the imaging chip are directly linked to the noise level of the data you are gathering, so I am now thinking that if I reduce the temperature from -3 to -10, I should see a reasonable improvement.  I still have one more set of data left to process from the most recent run of clear nights, but the next time the chance to get the observatory roof open happens again, I will be making this change to see exactly how much it helps.

Thanks for reading, and please continue to check back for more of my wittering soon.