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PostPosted: Sat Sep 15, 2012 9:33 pm 
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Not through processing, but by having more data! The subject here is a part of the veil nebula, taking with an OIII filter. 100% crops.

Image
This is the output of a single raw. Actually, I took out the red channel here since that has no data, only hot pixels. So just one single 4m exposure with the 600D at ISO1600.

Image
Let's take some more shots and average them. 15 shots in total to be precise. Much improved over a single shot. In the darker areas there is still noise apparent.

Image
Ok, how about even more data! 61 shots total here. The dark area noise has gone down some more. But this is 4 hours of total data...

With hindsight, maybe I should have stretched them all a bit more so that it gets closer to black background, as that shows up the noise even more by increasing contrast. Anyway, why do this? Well, I got the 15 shots earlier this month, but thought I'd see how much more data would give what sort of noise reduction. I think this is a reasonable level, so next time there's a clear night, I will also have to do it for SII and Ha data and have another go at a false colour combination...

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PostPosted: Sat Sep 15, 2012 10:44 pm 
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Hi popo,

Interesting comparison. Having been lulled by a brief clearing of the sky about an hour ago I fired up the 'scope but by the time Id got everything lined up the cloud rolled in and, contrary to the forecast, has obstinately refused to go away. So, instead of capturing RGB subs of the Soul I had a little play with your 15 shot stack using Topaz Labs InFocus and DeNoise filters only. here's the result:

    Image Image
    15 image stack cleaned up....................................................................61 image stack

I don't normally play with other's images but you have graciously given me permission to do so in the past. So, the question is how clean does the image have to be to be good enough? Four times the subs should, I think, increase the S/N ratio by a factor of two but I'm actually not seeing much more depth in that 61 image stack and the cleaned up 15 image stack isn't that far off. Given how difficult it can be to get any imaging time here in the UK I don't think the 61 image stack has justified the extra time spent at the telescope. Or has it? :?

Bob.

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PostPosted: Sat Sep 15, 2012 11:15 pm 
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The specific crop I picked above maybe wasn't the best. Here's another one I did on another occasion, but due to the limits of image hosting it isn't 100%. Again both are stretched similarly.

Image

I think it does make the faintest stuff easier to see through the noise.

I forgot to add these comparisons are not exactly like for like, as I finally got round to using flats for the 61 image stack, but not on the 15.

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.


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