M16, The Eagle Nebula

M16

This was my first and perhaps only image from the Almost Heaven Star Party. I attended AHSP last year for the first time but it was cloudy or rainy for the entire time. This year the weather was beautiful for the first night and while some clouds did come through later in the night it was after M16 had set.

The sky at AHSP is amazing. It’s 4,500 feet up on Spruce Knob and the Milky goes from horizon to horizon and nearly looks three dimensional it is so bright. The only downside is dew. Definitely bring dew heater straps and enough battery power to last through the. night to keep the dew away. If you are prepared you can image or observe the entire night without worry.

I have been wanting to image the Eagle forever but I can’t see the southern sky from home and opportunities to get to a club site have been rare for me. Clear nights and weekends have not lined up much. So this was at the top of my list.

However, before I could get to it, I had to work through some equipment issues. I set everything up and none of the USB2 devices were being seen. I tried unplugging and replugging, rebooting, different cables, cursing at the equipment gods, praying to the equipment gods and nothing worked. I discovered that my USB2 devices worked if I plugged my main USB3 camera directly into the computer so that’s what I did. I now had an extra cable hanging off the back of the telescope that I could not route well and my guiding suffered for it but at least I was back in business. However, I had wasted a lot of time.

The original plan was for three hours on M16 but I only managed 90 minutes before it was below 20 degrees. I didn’t think it would be enough, especially when figuring I’d lose at least some sub exposures. However, the sky was so dark that the individual subs looked great. When I got home and processed the images I ended up with 83 minutes of data. I feared I wouldn’t have enough to get a good enough signal to noise ratio but this turned out to be the easiest data to process I’ve ever produced. I knew an hour at a dark sky was worth several at home but this really proved it to me.

I had decided to only use RBG frames and forego luminance because it made processing simpler and there was a lot of talk indicating that luminance wasn’t really necessary with modern CMOS cameras. This turned out to be a good choice here. It was quite simple to process and I will likely continue the practice.

Speaking of processing, here were my steps:

The individual R, B and G masters were processed with Mure Denoise and then combined with Channel Combination. Then the combined master was processed like this:

  • Dynamic Crop (first approximation of final framing)
  • Dynamic Background Extraction
  • Photometric Color Calibration
  • Masked Stretch
  • Local Histogram Equalization (using starless luminance mask)
  • Multiscale Linear Transformation (mild sharpening using starless luminance mask)
  • Curves Transformation (contrast)
  • Adam Block’s star de-emphasis procedure
  • Dynamic Crop (final framing)

I had originally tried arcsinh stretch in place of masked stretch but the colors were coming out too saturated and it didn’t look good. I next tried the normal histogram transformation and the contrast was great but most of my stars ended up clipped. So I turned to masked stretch and it did a great job of bringing out the color without the stars overwhelming the image. The stars still benefitted from some reduction but it wasn’t nearly as bad as the HT stars.

While this may not be in Hubble’s class, the “pillars of creation” are clearly visible in the center of the nebula and lots of other structure is also visible. This is an interesting nebula to look at closely. There is quite a bit going on inside of it.

I wish I had more time on this at AHSP. But, even as it stands, I’m pretty happy with it! Oh, and he equipment problems vanished after that. Saturday was rained out but Sunday I powered everything up and it all behaved fine. I still have no idea what caused that glitch but I was able to return to my normal cable configuration.

Also, this was the first real test of my TeleGizmos 365 telescope cover and it performed wonderfully! On Saturday, thunderstorms rolled through all afternoon and it rained at least part of the night and my equipment stayed dry under the cover. I was nervous about that but it was just fine.

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