NGC 6820 and NGC 6823 - An Open Cluster w/Nebula - A Grudge Match…

Date: August 16, 2021

Cosgrove’s Cosmos Catalog ➤#0082

NGC 6823 & 6820: My Attempt to reclaim my honor after my first attempt yielded the image I hate the most in my collection! (click the image for full resolution via Astrobin.com)

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About the Target

Located in the constellation Vulpecula, NGC 6823 is a nice small open cluster of stars associated with a large emission nebula known as NGC 6820. These are part of an even larger faint emission nebula, SH2-86. Often this whole complex is just referred to as NGC 6820. The cluster is about 6000 light-years away and measures about 50 light-years across.

This target is not overly famous or well-known and does not have a common name that I can find. It is not photographed very often - but this is the second time around for me.

Why? Read on….

The Annotated Image

This annotated image is a screengrab from my account on Astrobin.com. For some reason, the Imagesolver Script that I usually use to create the annotated image was hanging up and would not complete.

Location in the Sky

IAU/Sky & Telescope Constellation Chart of Vulpecula with the location of the cluster and nebula indicated by a yellow arrow.

About the Project

Why shoot this relatively little-known target?

This is a grudge match. A chance to get even. An opportunity to reclaim my honor as an Astrophographer!

I first imaged this back on August 11, 2020 - one year ago.

I was looking for something to shoot that could be seen that night between my tree lines, and I saw this target on a star chart. Even though I knew nothing about it - I just decided to go for it. I used my William Optics 132mm platform - which at that time was running a One-Shot-Color Camera, the ASI294MC-Pro. I captured more than an hour and a half of subs and promptly produced arguably the worst Astro photo in my entire portfolio.

You can see that particular project Here.

And here is the image in Question:

Muddy. Ugly. Poor color. I hate it.

Here is the comment I added when I migrated that project to this website:

What can I say? I really don’t like this image. It was not chosen carefully. The capture was not planned out at all. The weather was not right. There is no nice composition to the frame. No wonderful colors or interesting details. Mostly muddy and blah! I said I would show the bad with the good - this is one that would be in the bad category. The only real value to images like these are as inspiration to do better - or at least never do any as bad as this again….

I am embarrassed to have this image in my collection. Who was the wise ass who thought it was a good idea to show all of my work - good, bad, or indifferent? Oh yeah - that was me.

At any rate, we had three very nice evenings in the first week of August - after a truly awful month of July - and I was looking for targets to shoot. I saw this target would be available.

I knew then NGC 6820 would again be on my target list. Oh yeah - it’s on!

Why was my image so bad last time?

• Poor skies - well, this time, the skies were clear and blue - Check!

• Poor Planning - not this time, Bucko. I have carefully researched things this time around. Check!

• Poor Composition - this time around, I used SGP to carefully frame the shot! Check!

• Not enough Integration - this time, I will PILE the hours on - I collected 11.3 hours - Check!

• I barely knew what I was doing during capture - Ok then, I had almost no clue, but this time around, I am packing at least half a clue - Check!

• I used an OSC camera for emission nebula - and they usually just come out red - Not this time - we are talking about a mono camera with quality narrow hand filters and the promise of Hubble palette color! Check!

• I barely knew what I was doing with the image processing - this time, I have learned much and am more skilled in Pixinsight-fu. I will process the living snot out of this target this time! Check!

Yes - This time, it would be different.

As I centered my scope on NGC 6820 - I noticed a slight shudder in the image. Wind? No - it was fear - NGC 6820 knew that it had finally met its match and would not be winning this round.

The Processing

I will add my processing notes to the end of this post if you are interested. It can get a bit repetitious as I tend to use the same approximate steps for images of this kind.

The Results

You saw my new image when you first started on this page.

You saw the original image as well.

Now let's see them side-by-side!

View fullsize

The First Attempt - sad though it may be (click to enlarge - but why bother?)

View fullsize

The newest attempt - hopefully, improved enough to clear my good name. (click to enlarge - recommended!)

Have I reclaimed my honor?

Have I vanquished my Foe - NGC 6820?

I guess that is for you to judge.

But as for myself, I feel I have fought a good fight, and I think I won this round. It may not be my best image. But then again, it is certainly not my worst image either. I feel I have conquered the beast and need not visit it ever again.

No longer do I hang my head in shame when hearing the name NGC 6820….

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Additional Info

Wikipedia: NGC 6820

The Live Sky: NGC 6820

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Capture Details

Lights

• Images were taken on the nights of Aug 2-4, 2021

• 47 x 300 seconds, bin 1x1 @ -15C, Astrodon 5nm Ha filter

• 41 x 300 seconds, bin 1x1 @ -15C, Astrodon 5nm O3 filter

• 48 x 300 seconds, bin 1x1 @ -15C, Astronomiks 6nm S2 filter

• The total integration time is 11.3 hours

Cal Frames

• 30 Darks

• 12 Flats Ha - taken each evening and applied to that night’s subs

• 12 Flats O3 - taken each evening and applied to that night’s subs

• 12 Flats S2 - taken each evening and applied to that night’s subs

• 30 Flat Darks taken each evening

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Capture Hardware

• Scope: William Optics 132mm f/7 FLT

  APO Refractor

• Focus Motor: Pegasus Astro Focus Cube 2

• Cam Rotator: Pegasus Astro Falcon

• Guide Scope: Sharpstar 61EDPHII

• Guide Focus Motor: ZWO EAF

• Mount: Ioptron CEM 60

• Tripod: Ioptron Tri-Pier

• Camera: ZWO ASI1600MM-Pro

• Filter Wheel: ZWO EFW 1.25” 8 slot

• Filters: ZWO Gen II 1.25” LRGB,

  Astrodon 5nm Ha & O3 filters,

  Astronomiks 6nm S2 filer

• Guide Camera: ZWO ASI290MM-Mini

• Dew Strips: Dew-Not Heater strips for Main and Guide Scopes

• Power Dist: Pegasus Astro Pocket Powerbox

• USB Dist: Startech 8 slot USB 3.0 Hub

• Polar Align Cam: Polemaster

Software

• Capture Software: Control: PHD2 Guider, Sequence Generator Pro controller

• Image Processing: Deepsky Stacker, Pixinsight, Photoshop, Coffee, extensive processing indecision and second-guessing, and much swearing…..

Click below to see the Telescope Platform version used for this image

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Processing Notes

Blink Evaluation

• 3 Ha frame eliminated as they showed a strange pixel pattern - seems to be a device error.

• 1 S2 frame was eliminated as it also showed a strange pixel pattern.

• No O3 sub elimination

• Subs all looked quite good.

WBPP script used to calibrate and align images

• Cosmetic correction used.

• All else default

ImageIntgration used to create Ha, O3, and S2 Masters

• Windsorized Sigma Clipping with thresholds clip thresholds of 3.5 and 2.5

DynamicCrop was used to trim the image.

No gradient was seen, and the image is almost all nebula, so no DBE was run

Deconvolution prep

Object mask created manually

• Local Support Masks created by using Starmask tool, default values except for 6 Layers

• Local Support Masks then had their contrast boosted about 25% using HT

• Psf image created using script PSFImage

Deconvolution application

• Object mask applied

• Psf file and local support for deringing applied to the tool

• 3 previews selected per image

• Tests run to determine the global dark value

• Ha: 0.004

• O3: 0.003

• S2: 003

Noticed some slightly elongated stars on Ha.

• Decon for elongated stars

• Ha - global dark 0.01

• Length default

• Angle 104

Light linear denoise run using MLT

• Not used for HA

• Used for O3 & S2

• 1(5,0.5,2)

• 2(3,0,45,2)

• 3(2.5,0.3.2)

• 4(1.5,0.3,2)

• 5(0.5,0.27,2)

• Mask - amp 300

Delinearize images

• STF-> HT transform

• Boost and adjust o2 and s2 using HT and CT

Channel combine in SHO pattern to create a color image

• Remove excess Green with SCNR

• Invert Image

• Remove excess Green with SCNR

• Invert Image

Boost contrast and sat with CT

Color sat - boost blues and golds

Do a nonlinear Denoise using ACNR

• Chrominance 4.5 with lightness mask

• Lightness 2.5 with lightness mask

Create a Blue color mask with ColorMask Script

Create a Gold color mask with ColorMask Script choosing GREEN

Run convolution on each mask to remove star rings - add a slight boost of contrast with HT

Apply blue mask and adjust tone scale and blue curves using it

Apply Green mask and adjust tone scale and blue curves using it

Some stars have some color I don't want

• Create Starmap using 8 layers

• Adjust mask star size with Morphological Transform and check with image stars

• Apply mask and Desaturate stars

Boost contrast of structures with sizes of about 70 pixels

• MLT - 8 layers

• Layer 6 bias +.005

• Layer 7 bias +.015

• Layer 8 bias +.005

• No mask

Local Histogram Equalization

• 0-bt lookup

• Scale 75

• Amount 0.15

A light, second application of ACNR

• Lightness 1.5 chroma 2.5

• Lightness mask

Shrink core stars that are blown out a bit

• Create a mask of cluster core using GAME

• Apply Morphological Transform 5 elements - "round" amount 50% with mask

Run EZ-Star Minimization using Adam Block method

Export file to 16-but unsigned TIFF

Run Photoshop, Load file

Round selection with 25-pixel feather and apply to large stars

• Use Camera Raw filter curves and color mix to tweak big star

Use free selection with a 120-pixel feather to highlight key image elements and do a slight Boost with Clarify and Texture tool

Apply watermarks and save.