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M42 new try, alt/azt, light poluted area


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A couple of things spring to mind here....... There's an obvious vignette (lighter in the middle and darker around the edges) - This can easily be dealt with using what are called flat frames. There's an excellent explanation here - Alternately there's a couple of software add ons that can help with this too to give you a flatter background (Gradient exterminator is a Photoshop plug in that works well) and there's a new filter from Pro Digital software called AstroFlat Pro that also works really well to correct vignettes. 

Then there's a background that is slightly dark....... If you make the background too dark (called clipping) then you lose any faint detail. I'm not sure how you processed this image (what software you used for example) but you want to keep an eye on the histogram while you are processing your image and always keep a little breathing room on the far left (that is a gap between the edge and the start of the histogram curve)

Hope that helps :)

Edited by swag72
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Lovely shot! It's always hard to battle light pollution, and you've done a great job here.

Apart from the vignetting (covered by other comment already), the other problem is that the white parts look a bit saturated. Not sure if that is in the subs themselves, or caused by the post processing. I'm no expert here, but I'd suggest maybe take more subs at a lower ISO. Possibly as many subs as you can get at ISO 800, and be a bit less aggressive with the levels adjustment in your photo editor. I'd welcome anyone else's comments on this - this is just what's worked for me when I've had similar issues in the past!

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2 hours ago, mislav said:

thnx..i will try that...how can i improve centre of nebula (to see 4 stars that can be seen on subs)

If your using Photoshop then this is a great tutorial for preserving the core. To get you "shorter exposures" without taking any extra subs, just duplicate the image at the start and use that.

http://www.astropix.com/html/j_digit/laymask.html

Edited by geordie85
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i will try this...So i wiil just copy one of mine subs and do mask layer on photoshop? Or copy stacked image and lower exposure to get visible center of nebula (if its possible)

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4 hours ago, mislav said:

i will try this...So i wiil just copy one of mine subs and do mask layer on photoshop? Or copy stacked image and lower exposure to get visible center of nebula (if its possible)

If you're using photoshop, take your stacked image and stretch it until just the core looks nice, then duplicate the layer and stretch it so the fainter detail further out is visible, this will blow out the core in the same way as your image above. Now add a layer mask to the top layer and "paint over" the blown out core so the layer underneath shows through... this might take some practice to get it looking nice and smooth, but should give you the desired result... then you've just got the vignetting to take care of, flat field frames will be your best friend here, once you've got a collection of good "flats" you can reuse them on a number of pictures and just update them every so often.

hth, Art

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