The Pelican Nebula is located just off the “east coast” of the North American Nebula in Cygnus. It is an emission nebula about 1,800 light years away and has an apparent size of about 1 degree by 1 degree in the sky.
This is eight hours of integration over two nights near new moon. The ASI1600MM Pro was at gain 15 and individual exposures were 60 seconds. The telescope was a Stellarvue SV80-3SV riding on a Sky-Watcher EQ6R Pro mount.Image was processed in PixInsight 1.8.7 and final touch up in Photoshop CS 2019.
PixInsight pre-processing was fairly straightforward. Calibrated using darks, flats and flat darks and did normal integration without drizzle or local normalization.
Here were the steps used on each R, G and B master:
- Mure Denise
- Dynamic Crop
- Dynamic Background Extraction
This was the remainder of the linear processing after using Channel Combination to combine the masters:
- TGV Denoise
- Photometric Color Calibration
- Curves Transformation
That last curves step bears some explanation. I used the GAME script to select the two bright stars that had massive halos and desaturated the halos a bit to tone down the chromatic rainbows that were there. Continuing on from there:
- Dynamic Crop (to final dimensions after I decided the initial crop wasn’t tight enough)
- Masked Stretch
- Curves Transformation (contrast)
- Star Reduction script
The star reduction does a pretty good job, but on some of the larger stars it selects it tends to create some darker ringing around the core of the star. I used the GAME script to generate a mask for these stars and applied it to the reduced image. I next used Pixel Math to copy in the original bits from the unreduced image. Overall it seemed to work well though it would have been nice to avoid the need.
Originally I had expected to acquire at least twelve hours of data on this but with two moonless nights of good data it turned out that eight hours was sufficient to get a pretty good image.