Cygnus Wall from the City Centre - Take Two...

[AMcD]

I managed to get five more hours of data on the Cygnus Wall last night from Worcester city centre, which I have spent the day combining with the three hours of data I gathered during the course of last week.  This second version of the image now comprises 8 hours of 5 min subs taken using a QHY8 OSC camera with an Optolong L-Extreme filter on a TS152 achromatic refractor mounted on a Losmandy G11.  Acquisition was undertaken using SGPro guided in PHD2.  Stacking was done in DSS and processing was undertaken in Photoshop - details below image.  As always, constructive criticism most welcome.  Many thanks for looking.

Cygnus Wall 26-29.8.21 Final Version.tif

 

ACQUISITION:

Luminance Frames: 

5 minute subframes with an Optolong L-Extreme filter.

QHY8 Gain 0 / Offset 120

Flat Frames: 

3.65s exposures on flats panel set to high (resulting in an ADU of 16000 against FWC for QHY8 of 25,000).

Bias Frames:

Taken at 0.000032 seconds.

STACKING IN DSS

Stack settings: "Average" for all sub-frames.

 

PROCESSING IN ADOBE PHOTOSHOP

Cropped the image to remove stacking artefacts so as not to affect the histogram during processing.

Removed gradient using medium/medium in Gradient Exterminator, feathered at 55px.

Applied levels to set black point for each channel.

Converted to a 16 bit TIFF file using "Local Adaption" in HFR.

Set the black point using 'Levels' in each channel.

Stretched the image using curves.

Further adjusted black point levels and repeated stretches using curves as necessary.

Moved to Carboni's Astronomy Actions to reduce stars and enhance contrast.

Applied a fine / low Gradient removal using Gradient Exterminator.

Re-checked levels and colour balance.

 

Edited August 30, 2021 by AMcD
Link to Tiff file added and workflow added.

[Lee_P]

It keeps getting better! Have you cropped in at all? I can see a thin pink line at the bottom and right, which may be a stacking artifact. The edges of the frame also look a little bright, might be an issue with ABE / DBE. It's a bit unusual though, I kinda like the effect 😃

[AMcD]

35 minutes ago, Lee_P said:

It keeps getting better! Have you cropped in at all? I can see a thin pink line at the bottom and right, which may be a stacking artifact. The edges of the frame also look a little bright, might be an issue with ABE / DBE. It's a bit unusual though, I kinda like the effect 😃

Many thanks Lee.  I have cropped it in.  I have been experimenting with putting a black border around the image in PS so I wonder whether the think pink line is an artefact associated with the borders between layers.  The line is not apparent in the Tif file when I open it in PS so it might also be a function of converting the Tif to a JPEG for posting on SGL.  I too noticed the brighter edges to the image.  The strange thing is that they were at the edges of the original and appeared to move in when I cropped off the stacking artefacts 🤔.   The weather tonight is looking half promising for more data - although presumably there is a law of diminishing returns that operates?

[Lee_P]

1 hour ago, AMcD said:

The weather tonight is looking half promising for more data - although presumably there is a law of diminishing returns that operates?

I've actually written an article about that: http://urbanastrophotography.com/index.php/2021/06/14/how-to-get-long-integration-times/

The short of it is that you do get diminishing returns, but you can keep going for quite a while and still see tangible improvements. The exact figures will depend on your kit and sky conditions. I aim for 16 - 24 hours of integration time per target.