M101 – Pinwheel Galaxy

Well after the first light of the 130PDS on Sunday evening, I had a night off the following day to catch up on some sleep! As it turns out, it clouded up at around 11PM so couldn’t have done anything anyway.

However the following day was an absolute scorcher compared with what we had dealt with for the past week or so. Temperatures rocketing upto 26ºC here in the West Midlands during the day, and not dropping much below 20ºC once the sun had gone down. But the night sky was clear, except for a very high layer of thin cloud that quickly dissipated as the evening progressed.

So I started setting up my tripod at around 10PM, first levelling it out on our uneven patio, then mounting everything else. By 10:30, Polaris was shinning over head and proceeded to polar align. However, this time I used the ‘Polar Scope Align’ application on my phone – an invaluable tool. This time, I didn’t use the eyepiece at all, and started straight away with the camera on the focus tube. I balanced the scope again after watching Dylan O’Donnel’s video on how to properly balance your scope.

Telescope properly balanced and waiting to be polar aligned.

After the awful attempt at a 2-star alignment for my M13 photograph, I decided to go for 3-star alignment and use my cameras crosshairs on live view to properly centralise the stars. For alignment stars I used Vega, Deneb and Dubhe, and I tried to get these exactly in the middle of the screen, finishing with the ‘up’ and ‘right’ keys to eliminate any backlash in the mount.

On the first alignment star, Vega, I used my DIY Bahtinov Mask to focus my camera, and it worked an absolute treat! You can see the diffraction spikes in the image below.

Once I had aligned with all 3-stars, I ignored the hand controllers ‘alignment error’ as I knew all stars were aligned correctly, and the error was around 1-minute in both right ascension and declination anyway, which I thought was good enough for a second attempt. I’ll obviously try and improve on my alignment as I progress, but for now it was easily sufficient for unguided subs with the 130PDS.

I entered M101 into the go-to and it slewed to it’s position. I did a rough text exposure of 30-seconds at ISO 6400, and got back an overexposed image, but could clearly see the faint arms of this beautiful spiral galaxy. At this point I got overexcited, as it was only 10:50PM and I was ready to start imaging! In my haste, I chose 120x 30-seconds at ISO 200 with a 5-second break in-between subs, which turned out to be perfect exposure at that time of night. So I went inside for an hour, and it suddenly dawned on me around 50 minutes later, ‘that’s going to be completely black when I go back out’. And to no surprise…I was right.

So at around half-past midnight I decided to do another set of 120x 30-second subs, this time at ISO 800. I could have pushed it up again to 1600 in hind-sight; it would have gotten more detail in the far reaches of the spiral arms. But I decided to play it safe, and not completely blow out the central core of the galaxy.

Once the imaging run had finished at around 1:15AM, I remembered to take some dark and bias frames. Luckily at this point, some high cloud rolled in and covered M101 in a haze. So there came another run of images with the lens cap on – I finally packed away at around 2:15AM.

So today after 6 hours sleep, I imported all the images into Deep Sky Stacker. I sorted through all the images to remove ones that were affected by either satellites, or cloud. I first tried the ISO 200 images and as I suspected, I could hardly see anything, even when stretched. So that line of images was abandoned – it was a waste of an hour or so of imaging, but you learn from your mistakes.

I tried all combinations of files; merging all exposures together to give a 2-hour 20-minute exposure, but the darker images just destroyed the lighter ones. I tried re-stacking everything about five times because I thought I could improve on the previous attempt. Alas, the ISO 800 images, along with the darks and bias, turned out the best. When stretched inside Deep Sky Stacker, I could clearly see the spiral galaxy, so I saved the final image, but ‘with edits embedded and not applied’ ticked, so my ridiculous amount of stretching wouldn’t appear in the final image.

In photoshop, I did a fairly aggressive stretch again with many interactions of levels and curves. Some people might think it is overly stretched, but that’s personal taste.

However, I did notice that there was little to no colour in the final image. I was expecting the typical vivid blue that you normally associate with the pinwheel galaxy. After doing some research on Stargazer Lounge and Cloudy Nights forums, it’s due to the way that Deep Sky Stacker handles the RAW files, and the saturation needs to be really pushed up in post processing. Once I did that, the vivid blue returned!

When that happened, I was truly blown away by the final coloured image! I was looking beautiful spiral galaxy, that had been captured with only a 50-minute exposure.

If I were to critique my own work, I’d say to get a lot more data; 2-4 hours would probably be a reasonable amount, going on what other people are doing. Also, I have some coma aberrations in the corners, but this could be corrected eventually by a coma-corrector. As I’m only just starting out though, to get an image like that on only my second attempt at astrophotography, I’m completely blown away with the end result!

It’s difficult to comprehend that photons of light have travelled for 20.87 million years to enter my telescope, be reflected off two mirrors and finally be collected by my cameras sensor! The human brain cannot comprehend the distance between us at this incredible galactic structure.

Wonder what my next target should be?

Till then, clear skies!

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