M42 at prime focus

While on vacation in beautiful Kentucky, I had a chance to try out the scope in some great viewing. With limited time and clouds moving in, I decided to try again at M42, since it is easy to find. The camera was used in “prime focus,” without any eyepiece used. I was eagerly awaiting a UHC filter coming in the mail, but I wasn’t able to try it out yet.

I took about 40 pictures at 1/3s exposure and 2000 ISO. They all stacked perfectly in Siril, and the result was opened in Gimp. The picture was quite noisy at that ISO, so I needed a way to reduce that. I recently learned about wavelets, so I was going to try that out on the image.

The first step was to brighten the image using series of levels corrections, moving the middle clamp to the bright side of the histogram, and the low cutoff to the left of the histogram. This made the nebula pop in the image. After that, I needed to remove the pinkish light pollution glow. This was easily done with a couple of layers filled with gradients.

Next, I used the wavelets decompose plug-in to break the image into five scales of detail. This worked remarkably well on my now noisy image. I used a simple Gaussian blur on the three smallest-detail layers, removing the fine color noise from the camera sensor. The two other layers were blurred just a little bit with a selective Gaussian blur.

Finally, I played around with the colors a bit to get some better separation between them. And, voila!, a decent photo with only about twelve seconds of total exposure!