Images of Andromeda Galaxy are what got me interested in astronomy and, more specifically, astroimaging. When I began imaging in earnest, last March, it was the tail-end of galaxy season and I really didn’t have a clue about my equipment. Still, my first DSO was a galaxy – it was a blurred, over-exposed image of Bode’s Galaxy but it was my first image and I was so excited. Suddenly, I began to realise what I was getting in to. These objects are so distant, that we really cannot comprehend the distances. We measure them, not in units of length, but by how long it takes light to travel across them. The thought of capturing photons that have been travelling for millions of years is what keeps me absolutely captivated by astrophotography.
I was too late to image Andromeda last season – and to be honest, I couldn’t even find it when I tried! Since then, I have learned a lot about imaging and the equipment I use. I am passionate about my imaging and processing; I refuse to listen to people who tell me that my skies are too light polluted and that I cannot hope to capture and process deep space images unless I am prepared to travel to dark skies. So it was with anticipation that I waited for Andromeda to reappear on the eastern horizons this month.
I also wanted to get back to using my DSLR as it is a lot easier to point and shoot rather than mess around with LRGB filters. I am back at work and so I want to be able to set up my kit mid-week and leave it running unattended over-night. I recently had my DSLR astro-modded (the IR and UV filters removed). I know that this is more for capturing nebulas however I feel it will also help a little on all DSOs. The work was completed by Andy at Astronomiser and I’m delighted with his work and service. I had the camera back within 10 days and in perfect working order.
I found myself with a clear night on the 21st September – the forecast all week had suggested I might have a couple of hours however, on the morning, the forecast opened up and I had 7 hours of clear skies from 9pm through to light at 4am. I opted to use my Skywatcher ED80 refractor rather than a newtonian as I really wanted to set up, lock focus and then go to bed rather than have to worry about the temperature, collimation and so on.
By 9pm, I was polar aligned thanks to Sharpcap’s polar alignment tool (can’t rate this highly enough) and I just had to wait for Andromeda to rise above the tree line. I got my scopes focused on Vega using my Bahtinov mask, before locking off and programming in my session into BackyardEOS.
I haven’t done much LRGB imaging – all sumer I have been honing my skills on narrowband – and so I wanted some advice on settings etc. A quick chat with Trevor from Astrobackyard.com helped me decide to work on ISO800 and use the histogram to find a good exposure duration. I ended up on ISO 800 for 180 secs as it gave me some separation on the left of the histogram, without moving too far to the right. I ended up running 100 exposures as I had the time to do so, and wanted to grab as much signal as I could for stacking.
The processing took me most of Saturday – I wasted quite a bit of time in Pixinsight but the stack it created had come real issues (I think that using bias frames was a problem) so I re-ran quickly in Deep Sky Stacker to see what happened. This time the stack looked good so I moved it back into PixInsight for processing.
The main problem in processing Andromeda is that the core is so bright, so any stretch results in the core quickly becoming white clipped. I worked using progressive masking to stretch in increments, masking each new stretch to ensure that the core or stars never blew out. This is a technique I have started using and I think it works brilliantly in terms of bringing out detail, even from light polluted skies.
I’m really happy with my result – it is probably my best process to date – but there are some issues that annoy me. There is some horizontal streaking that I have since learned is called ‘walking noise’ and is caused by a lack of suitable dithering. Strangely, I had wondered that the final stack didn’t seem to have much in the way of borders to crop, especially as it was a 5 hour stack. Looks now like either the dither in BYEOS wasn’t enabled or, more likely, it was dithering but not by enough. Another lesson learned. I have plenty of time on Andromeda this year so I will be imaging a lot more galaxies this winter.
Higher resolution on my Astrobin account