A somewhat circuitous journey has led to the publishing of this image. Two factors / variables have led to me imaging the same area three years apart which is maybe a good thing as it doubled the amount of data available. However, it was not planned that way. Let me explain as it makes for a moderately interesting story . . . 

Three years ago, in August 2020, I imaged the galaxy NGC 4517 in the constellation of Virgo. See thumbnail below for a link to the image. "Looks the same is this one" I hear you say! It looks the same because it is the same field. The first of the two factors that led me to image the same field are that due to errors in the catalogue, the galaxy NGC 4517 has a duplicate designation of NGC 4437. I thought I was imaging a new object with NGC 4437 but I wasn't. The second is that somewhere along the path of time since imaging NGC 4517 (the first time!), I had rotated the camera 90 degrees so I didn't recognise the object due to the different orientation when the data were coming in off the camera. It wasn't until I was processing the image that I noticed the errors in the NGC numbers and that I had already been there. So what to do . . .

The obvious thing to do was to combine the data sets and reprocess the data so this is what I did. A total of 19.5 hours of data from 2020 were combined with 17.5 hours of data from 2023 using the Weighted Batch Preprocessing Script in Pixinsight (along with the requisite calibration frames) to produce four nice new masters for Luminance, Red, Green and Blue. In addition I created a super luminance by integrating the Lum, Red, Gre and Blu masters. Given that I had plenty of data on hand, I used the drizzle option to increase the resolution of the masters which also gave me a better result in cropping in a little closer. Subsequent post processing was completed in Pixinsight.

I feel that I've been able to bring out more details in the galaxies though I was a little surprised by the amount of chromatic noise that I had to deal with. Though deal with it I did with the benefit of Russel Chroman's set of processes NxT, BxT and SxT. Many thanks to @Niall MacNeill for the pre release review of this image and excellent feedback.



NGC 4517 in Virgo