Messier 51 or M51 and its companion NGC 5194, shot during 7 different nights in the period of 15th till 26th of April 2020. With a total exposure time of 20 hours.Limited view...
My Backyard is surrounded by houses and trees in all directions, but during spring I get a chance to image the Virgo and Coma region around midnight. With all its beautiful galaxies filled across this region, it’s hard to pick a target and stick with it during multiple imaging sessions. It’s just very tempting to move to another target and see what the telescope can capture, if you’re as curious as me.
But, before Virgo and Coma came into view I decided I would spent some time on imaging one of my favourite subjects in the night sky.
It had been two years since I last imaged Messier 51 or M51 and its companion NGC 5194, and wanted to make good use of the seeing conditions that were predicted for multiple days to create the best image of M51. At least what I could make of it :). Also, M51 would be around Zenith which is perfect for my Backyard, and of course seeing (the lower you get in the sky, the more air the light has to travel through).
Can I spot it myself?
Sure! With a good pair of binoculars you could spot a 'fuzzy' near the Big Dipper at this location:
How it's done, in a nutshell.
To deliver a ‘wall grade image’, a publishable image which wouldn't look out of place on your wall, we need multiple exposures of the same object and stack it in specialised software. To give you an idea; my M51 image has 20 hours of exposure time, which equals 120 frames of 10 minutes. It was collected over multiple nights.
The individual images need to be stacked (this is done in specialised software). It reduces the noise (from atmospheric conditions, tiny tracking errors, satellites, camera noise) by looking at constant returning light signal in each frame from stars, galaxies and nebula. And it increases the Signal.
When the stack is finally complete, the processing begins to extract all the faint details and colour, this is done by hand in either PixInsight, Astro Pixel Processor, Photoshop or even Deep Sky Stacker. The software and skills needed for post-processing is just as important as the hardware that collects the data. I've seen myself destroy my images multiple times in the past, just because I needed to learn the basics of post-processing the data. Sometimes it's just better to reload the stacked image and start over. It's very difficult to get it right.
Perfection
I have started over processing the image multiple times. Just because I felt the real detail and colours weren't perfect. And each time a full process of the data can take up to several hours... To be honest, I just wanted this image to be perfect, and make it 'wall grade image' ready.
R, G, B and L
The camera I use is an Atik 383L+ Mono cooled CCD which collects light in black and white. Mono camera's don't use a bayer filter, which is normally needed to create a colour image from a sensor. Instead, we use R, G, B and L filters that only allows a small part of the spectrum to reach the sensor. Because no bayer filter is needed, all pixels on the sensor can be used to collect just one part of the light spectrum at a time, which makes the mono camera extremely sensitive. The CCD camera is cooled to a maximum of 40 degrees below ambient, to reduce noise. The image on the rights shows how one frame of 10 minutes on the Luminance channel looks like.
In total for Red, Green and Blue 30 frames of 10 minutes were collected at 2x2 binning mode. For Luminance (which in essence is a combination of the R, G and B spectrum) a total of 85 frames were used, a bit more than 14 hours.
The fainter details
At around 15 hours of total data collection I was a bit disappointed because I really wanted the fainter outer arms to be more visible. So I added another 5 hours just for that, and I'm happy I did.
At the second to last step, during post-processing, the galaxies were still a bit 'fuzzy'. One very careful sharpening was applied while protecting the background and stars with the proper use of masks. The difference was mind blowing.
Jaw dropping moments done easy
The most interesting part of this was, quite frankly, the most simple one. Cropping the image. I stared at it for a few minutes, because I just couldn't believe the amount of details I managed to squeeze out of the data, haha! Just... look for yourself and scroll down please :D
See you in two years M51 :) !
Cheers and Clear Skies!