As some of the more regular followers on Facebook will know, one of the biggest issues I’ve been up against is that I’ve not been able to manage more than one minute exposures. The reason for this, primarily, is that I haven’t been able to sit down and really look properly into guiding, and when I WAS able to, the exposures were worse.
After taking advice (LOTS of advice) I was finally able to trace the issue to my declination drive. So I stripped it, after having a closer look and realising that the gears weren’t seated properly and were causing the rig huge amounts of backlash, and reseated it all.
Due to the weather, I wasn’t able to get out and properly run it until the last full moon. Working up in incremental steps, I was able to get solid 5 minute exposures. Admittedly that was with a 50% loss rate, so there’s obviously more work that needs doing to fine tune it further, but it’s a great feeling knowing I’m on the right track and finally able to guide.
On top of that, as if for me that wasn’t enough, I’ve also managed to get all of it working in APT (AstroPhotography Tool). I’ve also got it working in NINA (Nightime Imaging ‘N’ Astronomy) but have yet to test that under live conditions.
Both APT and NINA use a process called platesolving, which is where the software takes an image of the sky, and resolves it against an internal database in order to figure out where the telescope is actually pointing. This might sound more tedious than carrying out a star alignment, but I personally find it more interesting. I’ll explain more about alignment procedures in another post.
APT connects to PHD2 (the guide software) and Platesolve, plus various other bits and pieces. Once it’s all connected you can then do everything you need to do within APT itself. More or less the same goes for NINA as well, and this includes control of the actual imaging camera and controls. The above image is a screenshot from APT showing Messier 27, the Dumbell Galaxy as a single 5 minute exposure.
How Guiding Works
The principle of this is really quite simple. A smaller scope, the guidescope, is attached to the rig somewhere, and is aligned with the main scope. Attached to the guidescope is a camera, the guidecam. This is what PHD2 uses for guiding purposes. In an ideal world, PHD2 picks a star, locks onto that, and keeps the scope perfectly aligned with it. Astro imaging is far from a perfect world and there are a lot of factors that make it problematic. Flex between the guiding setup and the imaging scope, mechanical issues with the mount, cable snagging, to name only a few. Assuming we’re in an ideal world, with the mount rock steady on the guide star, the main imaging camera can take long exposures of the target whilst maintaining pinpoint stars across each exposure. The longer the exposure, the more detail can be obtained.
And that’s it in a nutshell.