The M5 Globular Cluster

I’ve been meaning to attempt a globular cluster again after my success with the Orion nebula, but hadn’t really looked into it. Amazingly it was a Facebook memory that showed me my M5 image from a year ago, so I knew M5 was back in the night sky and I remember it being easy to find last time.

Once again M5 was simple to find, only taking a minute or two. The difference this time was I used my 2x focal reducer lens. By having a slightly larger field of view M5 should be a bit smaller (and therefore brighter per pixel), and it would travel slower across the field of view.

I used my ZWO ASI290MC camera set to 100ms exposure and 575 gain, used my 2x focal reducer, and 8 inch dobsonian telescope. This time I didn’t take a video, but recorded a series of photos.

I ended up with nearly 1000 images, but it was a nightmare to process these. Autostakker and DeepSkyStacker both failed to align and stack my images. I had to do some initial level adjustments in DarkTable to pull out the details in the stars to give the software something more solid to align on.

Even then I couldn’t stack all at once, I ended up doing 20-40 images at a time in AutoStakkert, and then stacking all those resulting images one more time. It was kind of a two level stacking system, and I have no idea if that’s a bad idea but it seemed to work ok.

My guess would be that my images are too noisy, the gain was simply too high. Next time I’ll have to make a slower shutter speed and bring that gain back down. Also waiting until later in the night when it’s darker (and M5 is higher in the sky) would be better. In the end I got a good image and learned a few things for next time!