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Sh2 181 Very Dim Sh2 Object GHS Tutorial, 



    
        

            jerryyyyy
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Sh2 181 Very Dim Sh2 Object GHS Tutorial

Getting plate-solving status, please wait...
Sh2 181 Very Dim Sh2 Object GHS Tutorial, 



    
        

            jerryyyyy
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Sh2 181 Very Dim Sh2 Object GHS Tutorial

Acquisition details

Dates:
Nov. 18, 2022
Frames:
Antlia Blue: 6×45(4′ 30″)
Antlia Green: 6×45(4′ 30″)
Antlia Red: 6×45(4′ 30″)
Chroma H-alpha 5nm Bandpass 2": 5×450(37′ 30″)
Integration:
51′
Avg. Moon age:
23.93 days
Avg. Moon phase:
31.54%

RA center: 00h49m22s.897

DEC center: +65°1307.96

Pixel scale: 0.824 arcsec/pixel

Orientation: 0.333 degrees

Field radius: 1.269 degrees

WCS transformation: thin plate spline

More info:Open 

Resolution: 9200x6200

File size: 37.1 MB

Locations: Stanford Faculty Observatory (Bortle 6 SQM 18.6), Stanford, California, United States

Data source: Own remote observatory

Remote source: Non-commercial independent facility

Description

People are asking me, so I am going to put up the GHS stretch steps for this very explicitly as it is a good example of a very dim object enhanced with GHS. 

My original image was 7h with the CCD:


Sh2 181 Another Faint Sharpless2 Object


Here are the steps to using GHS with this dim target now down to 51m acquisition:

Step 1:

Take the dim Ha and apply noise and star removal (see history explorer)

Use the 250% Zoom to the linear Ha image so you can see the now narrow histogram and put the symmetry point at the middle of the now very narrow peak.



Step 2:

Send the symmetry point and see how you now have the "S" curve on top of the linear peak.

Increase the Stretch Factor until you see something in the preview.... in this case I did not have to modify "b" but you may have to to optimize

APPLY this to the image


Step 3:

Reset the Zoom to 1 and you will now see a normal histogram for final adjustments... the dark point and maybe "b" will move the histogram back and forth left to right as the "S" intensity changes.



Step 4:

Reset GHS in lower right corner

Change the Transformation to Linear

Click the button to the right of Low Clip to set the bottom of the blacks... move the histogram to the left

APPLY this also



Step 5:

Last step put the symmetry point at the top of what every histogram you want to "S" curve in the now stretched image... could vary in color image
Note you have done the main work but you need a Stretch for the "b" to work

There is the "dim" Sh2 181.

APPLY this final tweak also.



Hope this is of some help with the essentials.

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