Andromeda is one of the classic astronomical images but is notoriously difficult to get right because of the range of brightness from inner core to outer spiral arms. It’s also a large object and requires a wide field scope.
I planned to use my WO Zenithstar for this as it’s focal length is probably about 380mm with focal reducer attached. I’d also read that light pollution filters suppress colours in galaxies so I used a HEUIB filter instead of my usual CLS filter. (Hydrogen alpha Enhancing UV and IR Blocking).
This was the first time I had used a Astro Hutech (round) drop-in DSLR filter. Previously, I had used Astronomik (rectangle) filters and had noticed a 4 spoke diffraction artefact around bright stars with long exposures and wondered if it was due to a rectangular object in the light path.
Guiding was good and I got the following exposures using Backyard EOS to control the camera.
9 x 30s, 10 x 60s, 10 x 300s, 5 x 600s
So that’s 114.5 minutes of data in total. A range of exposures was used to blend the bright core and faint spiral arms together.
Dew was just starting to gather on the scope by the end – not usually so much of a problem for refractors but at this stage, the scope had been pointing near Zenith for over 2 hours.
Unfortunately, I made a mess of my dark frames by setting the camera to JPG rather than RAW and I also found the lack of a light pollution filter produced a brown washed-out mess at the end of the night but I was able to use PixInsight’s colour neutralisation and colour saturation tools to rescue things eventually.
On the plus side, the diffraction artefact was gone. I think for my light polluted site, I’ll just stick with CLS light pollution filters but go with the Astro Hutech round version.
WO Zenithstar 420/71mm with 0.7 focal reducer, Modified Canon 60D at ISO 400 with Astro Hutech HEUIB filter. Ioptron ZEQ25GT mount with Orion SSAG/PHD guiding.
I have marked in Andromeda’s 2 companion elliptical galaxies, M32 and M110 plus a bright star forming region in Andromeda, NGC 206.
Andromeda has many more globular clusters than our Milky Way galaxy, and several of them can be located in this type of image by comparing against charts, I’ve marked 3 so far. They all have G designations, eg G111.