M81, Bodes Galaxy: Yes, you can image DSOs with an AZ mount (but don’t freeze your laptop)

This was probably the first image I was pleased with. It was also my first all-night session, in March 2020. It’s also the one where I froze my laptop – as in, literally froze it.

It’s M81, the Bodes Galaxy, with M82, the Cigar Galaxy.

M81 and M82. Click for full size.

It was one of my last captures with my old Sky-Watcher 130P AZ mount. I had replaced the OTA with a 130PDS, but was still using the mount. It’s a great starter set-up, but the AZ mount is not really suitable for DSO image capture.

Alt-Azimuth mounts are great for observing. They’re just up/down/left/right – easily understandable. You just point. And if you have a Goto, it will then track that object.

However, while AZ Goto mounts follow objects across the sky, they don’t rotate with those objects. An object will rise in the East, rotate as it moves across the sky, and then set in the West, and all the while, the image you capture from the AZ mount will show that rotation. So, when you come to stack all those images, you find that all the stuff around the edges isn’t really usable. It’s called field rotation.

They’re also not terribly accurate. They’re more intended for viewing than imaging, so absolute pin-point accuracy isn’t as important.

That’s where Equatorial (EQ) mounts come in. They track objects precisely, and keep the camera oriented to those objects too.

There’s also a cautionary tale behind this shot.

The night was wonderful – clear, not too cold, a great time for me to do my first ever full-on, all night imaging session.

Once I was sure everything was set up right and working, I took myself abed, leaving the heavens to wheel above me and my kit to capture them.

I woke up early, noticed it was a bit parky outside. Frost. Everywhere.

A bit panicky, I ran to the setup. It looked ok but there was frost on the laptop. When I started it, it went ‘crunch’. This is not a good sound for a laptop.

After leaving it on the radiator for while, it then went ‘swoosh’ and did nothing. After a bit longer it started to go ‘whirr’ and showed a message about Windows not starting, but suggesting I could try restoring it automatically.

Against all hope, it turned out my system had in fact been backed up automatically the day before, and I gingerly started the restore process. It actually worked. It actually, actually worked…

And that’s when I bought a box to keep everything in overnight. Well, you would, wouldn’t you?

Nerdy stuff:

  • 7 hours of integration
  • 30 seconds exposures at ISO800
  • Hardware: Sky-Watcher 130PDS scope (F5), Sky-Watcher AZ Goto mount, Canon EOS1000D astro-modded camera with Sky-Watcher 0.9x coma corrector
  • Software: capture with Astrophotography Tool (APT), stacking with Deep Sky Stacker (DSS), post-processing with StarTools and Photoshop CS2
  • View annotated at Astrometry.net
  • View superimposed against the WorldWide Telescope

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