Swirling Down the Whirlpool Galaxy

The weather hasn’t been especially great for view or astrophotography this past month, which might be a blessing in disguise. I took what I thought were going to be some great images of the Whirlpool Galaxy, Messier 51. I had 4 hours of good 5-minute exposures in pretty clear skies, but I guess there are just limits to what you can do when you’re pointing your scope over the umbral of city light.

M51 was one of my first DSLR astrophotography targets almost a year ago. I previously discussed my early process and equipment, but I can at least share one of those older images here for context and convenience.

Processed 7-12-2020

You can see how the light from the city creeps up into the image. The closer to the horizon your scope gets, the worse it becomes. But, the sky didn’t look too bad that night I set out to grab 4 hours of exposure.

I believe my first mistake was I started too early. The sun was set, but there was still some of its ambience in the “night” sky even though I could make out my DSO of choice. It wasn’t until I started to stack and process the image that I began to see the issue. It’s pretty telling.

Even though I dutifully captured my flat and darks, neither seemed quite prepared to overcome the result. Hour to hour during the image capture, that light you see in the bottom of the photo above as a reference, would shift lower and lower. So after stacking and even using GradientXTerminator, you could still see “waves” of light in the background of my data.

After multiple attempts to process the image in Photoshop, I decided to restack the raw files, but exclude at least the first hour of imaging to reduce the light pollution I was getting. Here’s what that looked like after some basic image adjustments. Because the image is cropped and depending on your screen, it can be hard to make out the waves in the background. Just note the bottom left corner is bright, then there’s a band of darker sky, then some brightness just above the galaxies, and then a darker corner. Also, there was not a lot of color.

Whirlpool Galaxy, M51, stacked and roughly processed image from exposures taken on 2-20-21.
Whirlpool Galaxy, M51, stacked and roughly processed image from exposures taken on 2-20-21.

Undeterred, and not having any new data to stack and process, I tried again. This time around, I applied a color-preserving luminance layer to preserve the star color and more gradually stretched the data with the arcsinh functions and balanced the light levels. Still, I think I oversaturated the image. It may look a little blue, but notice there are some orange stars, too.

Whirlpool Galaxy, M51, stacked and more carefully processed image from 3 hours of exposures taken on 2-20-21.

While I think this version looks better, if not prettier. It’s still not as clear and as detailed as I would like and I’m still seeing what I can only describe as a “flat” coloration where I would expect to see something that would more resemble nebulosity/clouds.

But really, I probably just need better skies and more Adobe knowledge. Do check out A.V. Astronomy’s video for some good tips and tools for quick image processing in Adobe. I learned about how to create the luminance layer and a method for removing light pollution from his video.

T-Shirt Trick Works and Learning More About Adobe Processing

It took a little while to perfect it, but the T-Shirt trick works for capturing flats. Unlike my previous attempts, I bought a clean, new white shirt. I gently stretched it over my scope and secured it with a rubber band. I made sure to maintain the same focus I used for my light frame exposures. And, the best trick of all, I switched my camera’s mode to “Av” on my Canon Eos Ra (an amazing Christmas gift from my brother!). The mode automatically picks the correct shutter speed to produce the proper exposure for the flat frame.

White T-shirt, somewhat stretched over my telescope and held in place with a rubber band. Makes all the difference.

As for my light source, I’ve been shooting in my backyard lately. So, once I finished taking my light exposures and my darks and I’m getting ready to pick up, I turn on my white LED porch light. From there, all I need to do is point my score at the light. It’s just as good as using an all-white LCD tablet or laptop screen or resorting to a light box. Except, it doesn’t do my a lot of good when I’m not shooting from my backyard. So, I’ll need to find a good portable light source when I’m working remotely.

Here’s the result of plugging my new flat frames into Deep Sky Stacker and doing some newbie image processing on them in Photoshop. It looked so nice, I had it printed and matted at FedEx Kinkos. Ultimately, you can see how that distorted ring of brightness from the last post is gone now, averaged out by DSS with the flats!

Orion Nebula, M42
A couple hours of exposure time with flats and darks.

The next step for me is to learn more about image processing in Adobe. Right off the bat, I can share just how great the “arcsinh” curve stretches are for performing color-preserving stretches of the TIF file data. The guy who designed these stretches for PixInsight, which is the super expensive astrophotography editing software, created these stretches for Adobe and he explains it all in this post on the Cloudy Nights forum here. Definitely pick these up and install them if you’re using Photoshop for Astrophotography; they’re free.

Here’s a quick and dirty bit of imaging I did using the arcsinh stretches to draw out my images with only a couple hours of exposure time at my local observatory. Granted, the EOS Ra also helps a lot with image quality, too. And even still, there’s a lot that could be done to improve these images of M81 and M82, the Bode Galaxy and Cigar Galaxy, respectively.

M81 and M82, after a couple hours of exposure, some arcsinh stretching, and a really good DSLR camera.

I grabbed 4 hours of exposure time of the Whirpool Galaxy, M51, which was the deep sky target I cut my teeth on over last summer. Assuming I can find some time this weekend, I’m hoping to process that TIF file in adobe and try some more advanced techniques I learned, like creating star masks to preserve star color, tricks to remove light pollution, and (not so advanced) ways to “feather” my lasso’s deselections so I can play with the galaxy separate from the stars and vice versa.