Messier 33 (or M33) represents. for me, the most amount of data that I’ve collected on a single target to date, at exactly seven hours total integration time. This consists of 81 five minute “light” frames (or subs) and 11 three minute ones, plus dark, flats and bias frames for calbration, shot across 6 nights from mid September through early December, using my primary DSO setup; the 72ED, Altair GPCam2 290c on the EQ5 Pro.
The fact that it was captured across so many nights with such a long time frame meant that it came with it’s own set of challenges. One of these were the calibration frames. When I started this back in September, the nights were still reasonably warm and so the dark frames for then were more in keeping with the ambient temperature of early autumn, which was much warmer than mid December. Dark frames are temperature sensitive to the corresponding subs. As a rule of thumb its better to keep them within about 5 degrees of one another so that the darks can calibrate the subs correctly. Dark frames also need to be of the same exposure length as the subs they’re calibrating.
The flat and bias frames aren’t reliant on temperature or exposure times and so can be taken at any time. With regards the flats though, they’re reliant on no movement or other changes in the imaging train. I’ve personally found it best to shoot flats the following day when the rig is back inside, so long as you’ve made no changes and everything is exactly as it was when shooting the subs.
With the combination of the Altair GPCam2 290c and 72ED, M33 fits quite well in the field of view (FoV), although with the dedicated reducer/flattener for the 72ED it would allow the galaxy to fit even better and give some “breathing space” to the image.
One thing I’m only just finding out about is pre-framing the image using software such as Stellarium (below.) With something like Stellarium, you can input and save the parameters of your imaging train (focal length, resolution of camera etc) and it will then show you what your frame should look like.
I’ve yet to use Stellarium for this purpose properly but I’m looking forward to it on the next run out 🙂
One of the beauties of Stellarium is that you can also use it to control your mount, which is what I now do with Millie’s Celestron SE once I’ve done the alignment process for it.
M33 has so far been the most fun I’ve had with a single target. Once I start getting into narrowband imaging I’ll be adding more and more data to it. For now I’d like to add a further 3 hours using the OSC.