M13 images. Changes in capture and processing

[timh]

I've been working on old images and applying new processing methods. Clear skies back soon I hope!

Looking back over a year and a half the pace of change seems extraordinary. Just thought it interesting to illustrate this with a couple of M13 images as an example.

The top image is a PDS200 (8 inch) Newtonian image dated April 2021 of M13 -- it is a high dynamic range composition comprising 3 stacks of 1) 1200s of 10s, 2) 1200s of 20s and 3) 2000s of 40s exposures using an ASI 294MC camera. It was processed in PixInsight and clearly shows the famous M13 propeller as well as a few other dark lane structures and I remember being fairly proud of it at the time.

The lower image - on a smaller scale -is also of M13 acquired using the same telescope in July 2022. The approach here changed to lucky imaging - to try to improve resolution - with the luminance of 600 x 2s mono frames informing 110 x20s OSC frames. Again processing was in PixInsight but using some new tools which, aside from the effect of lucky imaging per se, further improved things. https://www.astrobin.com/p6ocey/F/


Firstly the image colour has come out completely differently from my first effort -- the image is much bluer showing a predominance of blue stragglers- but being quite confident that it is correct because it was calibrated using the the new SPCC spectrophotometric colour tool and Gaia database updates- I took care not to mutate it during processing.

Secondly the resolution of the second image is far better than the first (they are compared side by side in a third image). Partly this was due to the lucky imaging at 0.47 arcsec/ pixel -- resulting in frames at FWHM ~ 1.5 arcsec but largely also due to some new features in BlurXterminator which are useful for reducing not only the size of stars but also the haloes of saurated stars.

It is interesting to see how perception of some of the familiar dark lane structures of M13 start to get lost as the detail improves. Also I think that it illustrates that for objects like M13 and with CMOS cameras only quite short total imaging times are required.

Tim

[turfpit]

Tim

Another useful write-up. Thanks.

Dave

[timh]

Thanks Dave, it is useful for me too to write at least some outline of what I did - with processing methods changing and improving so fast it is easy to get lost in the many alternatives.