Over a week ago now I had an intense astronomy evening with my tame scientist. There weren’t many hours between sunset and moonrise so we worked fast to try and prove that we had a reliable autoguiding setup, having been plagued by various failures and obstacles the last few times we’d tried (see below)
We did a lot of testing, a lot of calibration and photographed several of the Messier objects. We didn’t have enough time to take many frames of each, or to capture many dark frames. As a result, these stacks are very noisy but are a good proof of concept that finally we have a satisfactory autoguiding technique. All of these pictures seem to have slightly reddish white balance but it’s not really obvious what colour the galaxies should be, and using a CLS-CCD filter doesn’t help because only certain wavelengths are permitted through.
This is Messier 104, the Sombrero Galaxy – so-named because of its dark brim. This is a stack of 6 frames and 3 dark frames, all shot with an exposure of 150 seconds at ISO 6400. In a future attempt when I have more frames I may try to drizzle the image to increase the apparent resolution.
This is Messier 64, the Black Eye Galaxy. This is a bit brighter than the Sombrero Galaxy so I cut the exposure down to 100 seconds at ISO 6400 to avoid over-exposing the nucleus too much. As before, there are 6 light frames and 3 dark frames.
This photo of M81 (Bode’s Galaxy, left) and M82 (the Cigar Galaxy, right) is edited slightly differently from the two shots above. Above, I clipped the darker areas of noise to black to make the background appear plainer. Here, doing that would have caused loss of detail in the faint spiral arms of the M81 galaxy so I decided to leave the background noisy. The right way of solving the problem is to take more light frames, and some dark frames.
This pair of galaxies was brighter again, so the exposure was 90 seconds at ISO 6400. There are just 5 light frames in this stack, and no dark frames. These galaxies were also relatively low in the sky over luminous Bristol on a somewhat hazy night, so the image was degraded by less-than-optimal atmospheric conditions.
In the past, I’ve had various problems trying to get autoguiding to work. In no particular order:
- Laptop power supply catching fire
- Forgetting to install the driver to allow the laptop to control the telescope (and no internet in rural Somerset!)
- Forgetting to account for daylight savings time after it changed in Spring
- Netbook having insufficient power to control two cameras and the telescope simultaneously
- Having a crap guide camera (a home-modified webcam glued into a film canister)
For those who are interested, my equipment this time:
- GSO 6″ f/5 (f=750mm) Newtonian telescope on Celestron Advanced VX mount
- Modified full-spectrum Canon EOS 600D imaging camera
- Astronomik CLS-CCD filter to kill off most light pollution
- TS-Optics coma corrector
- TS-Optics 50mm f/4 (f=205mm) guide scope
- CMOS guide camera
- HP laptop with Windows 7
- PHD autoguiding software
- BackyardEOS capture software
Jonathan Gazeley 