The Whirlpool Galaxy, sometimes known as the Question Mark Galaxy, or Messier 51 (to give it it’s catalogue reference), is one of the most studied and imaged objects in the night sky, in part because it’s so easy to image in almost any format, be it widefield or at higher magnifications, and it doesn’t take a great deal of exposure time to make out the larger components of it’s structures, which are impressive in their own rights. A large part of that is down to its surface brightness, and also that its circumpolar (never sets below the horizon) above certain latitudes in the Northern Hemisphere. Because of these factors, it remains a favourite DSO to image with astronomers and astrophotographers, including me.
I’ve experienced a lot of technical issues attempting to image anything in or near Ursa Major with my mount, the EQ5 Pro. Despite solid polar alignments, double and triple checking the mount was level, ensuring it was as balanced as possible and still a little “east heavy”, the mount would suddenly throw a fit at me in declination and just not remain on target no matter how short I made the length of the subs. I fully expected this evening to be no different, and initially I was proven correct.
Frustrated, I slewed to another part of the sky, in fact a complete 180 degrees, hoping to have a go at something, anything else…to be met with the same issue!!! She was NOT behaving herself at all!!
In the end, despite having already done it several times, I decided to do a complete recalibration in PHD2. This seemed to work on the target I was on (M42 as I recall), so I figured on returning to M51. Although there was a distinct improvement I was still losing more subs than I was saving, so I reran the calibration whilst on M51 itself. And that nailed it. All of a sudden, after many lost hours across the very few imaging-worthy nights I’ve had this winter, we were guiding again at 5 minutes. In fact it was that steady I couldv’e pushed 10 minutes easily if the graph was anything to go by! For the sake of consistency though, I kept it to 5 minutes, using the new ZWO ASI178MC. After taking several test images at 5 minutes, due to the amount of “amp glow” I decided to dial it back even further and run with 3 minute subs. I was still getting a lot of detail in the individual frames due to the increased sensitivity of the 178MC compared to that of my old GPCam2 290c
Weather conditions were less than optimal, with some high altitude muck to contend with, and intermittent fast moving low cloud, but overall they were at least favourable. The weather this winter season has been absolutely appalling in the UK, with very few opportunities to actually get out and image, so I was determined to stay the course with this.
Post processing the following morning was a bit of a nightmare. Despite having a full set of calibration frames, I was still seeing amp glow in the final image that for some reason hadn’t calibrated out. I’m still not sure of the reasons for this, but one of the workarounds I’ve seen is not to rely on a “darks library” with the ASI 178, but rather to shoot them at the end of each session. That’s going to be fun…NOT. Although in fairness the ASI 178 is better suited for lunar and planetary work (and it certainly performs the former with some pretty amazing results!)
Eventually, I was able to produce an image that I was happy with, despite there still being some uncalibrated noise and amp glow in the final shot (image below.)