Description
NGC 7023, also known as Caldwell 4 or “Iris Nebula”, is a bright reflection nebula in the constellation of Cepheus. It is approximately 1300 light years away from Earth and is one of the larger reflection nebula in the sky with a whopping apparent size of a total of 18’×18′. Inside the nebula is an open cluster and a bright BV class star which illuminates the nebula in a beautiful blue color.
Reflection nebulae are primarily illuminated by their stars and not bright enough to illuminate themselves (compared to emission nebulae). Thus the region around NGC 7023 appears fairly dark with no stars to illuminate the dust, giving it an appearance of a dark nebula. With no H-Alpha or OIII emissions narrowband filters would have not helped at all.
This time I decided to leave the RGB picture be and not integrate the lightness data from the 383L+ into it. Which led for the first time to a result of two different pictures of the same object. Thanks to the dual setup this was a breeze to make. Depending on the object I might continue down that route in the future. For the color data in the Newton image I integrated the D5100 RGB data into it.
Technical Details
Oh boy where to start. Typically for my latest Newton images it seems to be severely miscollimated and thus enjoys the coma. The Apo also seems to have some tilt or something in the image train, making the left side of the image pretty… well, not pretty at all. I tried to recollimate the Newton but somehow it didn’t work. Looks like I need to check the seconary mirror as well.
Oh yeah, and focus. Oh the focus. For whatever reason my Newt decided to not be focused anymore after I actually focused it. Next time I will definitely check and recheck the focus before I let the sequence run. I also don’t want to start lamenting about almost full moon, lots of wind, cold (summer, where?) and a lost SD card – but all of those were actually a thing.
Acquisition Details
Shot with Atik 383L+ on SkyWatcher 8″ f/5 PDS and Nikon D5100 on TS Optics 70mm f/6 APO FPL53 Triplet
Date: 2018-06-23
Atik L: 50×300s 1×1 binned
D5100 RGB: 110×120s 1×1 binned
Postprocessing Details
L (383L+)
- DynamicCrop
- DynamicBackgroundExtraction
- Deconvolution
- TGVDenoise and MMT by Jon Ristas method
- ArcSinhStretch
- HistogramTransformation 2×
- Dark Structure Enhance Script
- MultiScaleMedianTransform
- LocalHistogramNormalization
RGB (D5100)
- DynamicCrop
- DynamicBackgroundExtraction
- PhotometricColorCalibration
- SCNR Green
- MultiscaleLinearTransform (L)
- MultiscaleLinearTransform (Chrominance)
- ArcSinhStretch
- HistogramTransformation
- MultiscaleMedianTransform
- AutomaticBackgroundExtractor
L (D5100)
- TGVDenoise and MMT by Jon Ristas method
- ArcSinhStretch
- HistogramTransformation
- Dark Structure Enhance Script
- LocalHistogramEqualization
- TGVDenoise and MMT with a low contrast mask
- CurvesTransformation (Contrast)
LRGB (383L+ and D5100)
- Align RGB to L
- Resample 50%
- CurvesTransformation (Star Saturation)
- CurvesTransformation (Bright Region Saturation)
- CurvesTransformation (Contrast)
- Export to Lightroom as 16bit tif
- Export from Lightroom as JPEG
LRGB (D5100)
- MorphologicalTransformation to reduce star sizes
- CurvesTransformation (Star Saturation)
- CurvesTransformation (Bright Region Saturation)
- CurvesTransformation (Contrast)
- Export to Lightroom as 16bit tif
- Export from Lightroom as JPEG
Annotated Images
