Having focused on solar/lunar/planetary imaging the last few months, I was also anxious to try some deep sky targets. The nebula region surrounding Sadr is one of the earliest targets to rise in the evening this time of year, and I acquired this narrow band image over the past week. It represents one of the longer integrations that I have attempted (about 7 hours total, with 4 for H-alpha and 3 for OIII.) The 135 mm lens was set to f/2.8 for these images, with each sub-image 120 s. Settings for the QHY 163M camera were: gain=174, offset=50. The Crescent nebula appears in the upper right corner of the image. A few other smaller star clusters and a reflection nebula (NGC 6914) appear in this wide field view as well.

For this image, I mounted my telephoto lens on top of my 80 mm refractor with a set of tube rings, using the larger scope for alignment and guiding. It was difficult to achieve the proper spacing between the camera and the lens with the filter wheel included, and I spent several weeks trying to figure out the best combination. My previous narrow band set up was not very effective -- I had to disassemble the camera/filter assembly every time I wanted to switch filters. Ultimately, I ordered a custom-machined fitting to ensure a solid connection between the lens and the filter wheel (as well as the right spacing.) This combination was much better. I suspect I still need to add some shims somewhere along the optical path (looking at the stars away from center, there appears to be some tilt somewhere.) Another contributor here on Astro Bin (astropical) brought my attention to the benefits of the multi-star guiding feature in PhD2, which seemed to work quite well here.

For processing, I used Nebulosity to perform stacking, and PixInsight for most of the processing. I used StarNet++ to remove the stars so I could process the nebula itself separately (including stretching and noise reduction.) I later added the stars as a separate (more gently stretched) layer in using Paint Shop Pro.

I do really enjoy these emission nebulas -- it is very satisfying to capture them from my light polluted location. With summer fast approaching, I am very much looking forward to trying some more narrow-band imaging targets in our Milky Way!