First attempt at SHO image ... would like your feedback

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Andy Wray avatar
I took the below image of the crab nebula over the past 3 days.  It's 75 x 300sec exposures (25 each) through SII, Ha and OIII 7nm filters.  Any suggestions on ways to improve colours, detail, contrast, stars etc. would be appreciated:



My first attempt at the crab
andrea tasselli avatar
It seems to me that you clipped the shadows.
Jean-Baptiste avatar
Hello Andy @Andy Wray 

I like the details you got from M1, its sharp and without being "oversharpened" ^^

Some few comments:
In a general way:
- you have clipped the sky background which is almost at 0% , you could try to maintain the sky background at values between 6% to 15% this will give a more natural look especially if you pay attention not to stretch too much this background
- there is a residual gradient, from bottom to up, to handle at the very beginning of the processing in linear phase

More specific to SHO : 
- you can do what you want with colours in SHO, for my personnal taste, there is perhaps too many green in your composition, but this is only my opinion ^^ I must admit that with M1, I prefer HOO composition 
- the same for the stars colours, especially in SHO, you could try to manage stars colours either with a few RGB acquisition or with a dedicated composition for the stars : with Starnet v2, it is very easy to separate this processing, even without RGB data, you may try something like :
R: Ha
G: 20%Ha + 80%Oiii
B: Oiii

with this you will get stars colours "more natural", even if you maintain a SHO composition for the nebulosity
But as I said, you can do what you want, this is just to open you some doors that perhaps you haven't considered ;-)

Clear Skies
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Andy Wray avatar
Jean-Baptiste:
More specific to SHO : 
- you can do what you want with colours in SHO, for my personnal taste, there is perhaps too many green in your composition, but this is only my opinion ^^ I must admit that with M1, I prefer HOO composition 
- the same for the stars colours, especially in SHO, you could try to manage stars colours either with a few RGB acquisition or with a dedicated composition for the stars : with Starnet v2, it is very easy to separate this processing, even without RGB data, you may try something like :
R: Ha
G: 20%Ha + 80%Oiii
B: Oiii


Many thanks!  Very useful.  I have fixed the rookie clipping mistake and have applied your other two recommendations.  I particularly like the star pixelmath combination which I will use in future when I run out of time to do the RGB capture.
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Gamaholjad avatar
As above for stars use RGB. Also try adding the Ha data as a luminance in the pixinsight LRGB just uncheck the rgb, drag the settings onto your color image. The image should pop a little. Theres loads on option to adjust color on that function too. Play till you get an image you like. Your image is already great.
Andy Wray avatar
OK, here was my final process of this based on above feedback:



Crab Nebula SHO using a cheap newtonian