**M13 - Globular Cluster in Hercules**

Taken across a couple of moon-free nights in March I bring you Messier 13 - A friendly Globular Cluster in the constallation of Hercules. As always, feedback and constructive criticism is encouraged!

**Equipment:**

* Orion 8in f4.9 1000mm / Flocked / Mask on Turned down edge on primary

* Guiding with ZWO 60mm f4.6 guidescope and asi178mm camera

* ASI071mc one-shot-color cam

* Hutech IDAS LPS D1 Filter

* Celestron CGEM Mount

**Acquisition:**

* Lights: 887x30s taken across three night: 2019-03-17, 2019-03-18 and 2919-03-19: unity gain (gain 90 offset 65) and -10C from backyard (7hr 23 minutes) Dithered RA only once every 10 frames.

* Flats: 30x0.84s using t-shirt flats pointing at ceiling

* Dark Flats: 30x0.84s Same orientation as Flats with lid and jackets covering Optical Tube.

* Darks: 60x30s at -10C

* Bortle Dark-Sky Scale: 4.00

* Pixel scale: 0.981 arcsec/pixel

* Orientation: 8* degrees

**Pre-Processing with PixInsight:**

* Calibrated and stacked using [LVA PreProcessing Steps](http://www.lightvortexastronomy.com/tutorial-pre-processing-calibrating-and-stacking-images-in-pixinsight.html)

* Integrated best 887 of **1114** frames selected using a combination of Blink and Subframe Selector.

* No local normalization

* CFA drizzled 2x scale 0.7 drop shrink

* Crop with Dynamic Crop

* Dynamic Background Extraction

* Background Neutralization

* Photometric Color Calibration

* RGB Working space to 1,1,1

**Luminance Processing**

* Extract Synthetic Luminance for Deconvolution

* Deconvolution with a Dynamic PSF L |> select 16 samples from around the outer proximity of m13 |> Export PSF

* Starmask for local support 0.3

* Global Dark: 0.004

* Global Bright: 0.0015

* 3 layers of Poisson wavelet regularization

* Fix 3 brightest star cores that deconvolution introduced internal rings on by replacing them with the non-deconvolved image (clone stamp to create mask of the broken stars + pixel math ``L_Orig`` )

* Extract Synthetic Luminance for Noise Reduction

* Small Scale noise reduction using TGV Denoise

* Medium Scale Noise reduction using MMT

* Combine Decon image with NR image using a clipped and blurred luminance based mask and PixelMath ``L_Decon`` and ``L_NR`` with the mask inverted

* Stretch using masked stretch using a "Preview aggregator" of 5 different background previews as background reference.

* Applied 5-layer HDR using Median transofmration to back off the intensity of the globular's inner glow

**RGB workflow:**

* Small Scale noise reduction using TGV Denoise

* HSV Repair script to tackle over-saturation HD 75700 (Brightest double star)

* Arcsinh Stretch to stretch non-linear

**LRGB Combination with 0.7 on L and 0.3 on saturation**

* Two rounds of curves to enhance contrast raise background level and increase saturation

* ACDNR and MMT to remove large scale chrominance noise in the background

* Crop for framing

* Save as JPEG