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Re: [ccd-newastro] Removing background noise

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  • Mark Striebeck
    completely different thought: For my DSLR camera I used a light pollution filter which made a big difference. Is it possible to use a light pollution filter
    Message 1 of 43 , Sep 6, 2013
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      completely different thought: For my DSLR camera I used a light pollution filter which made a big difference. Is it possible to use a light pollution filter plus the LRGB filters? Or would that weaken the signal way too much?

           MarkS


      On Fri, Sep 6, 2013 at 6:04 AM, Dean S <dean@...> wrote:
       

      Hi Mark,

      I image from a yellow/orange zone and have a difficult time with noise as well, particularly with RGB. Best way I have found to deal with it is many, many subs. And don’t let the background levels get too high so shorter subs may be called for, and pick the best nights for doing RGB. The less stretching you have to do on the image the less noise you will show.

      I tend to leave my image backgrounds a bit on the lighter side as I do not like a clipped black background. That looks unnatural to me so I have to be careful about background noise.

      Noise ninja is a nice tool for smoothing, but smooth noise can look bad too.

      Here is an image I am working on now. I have 24 x 5min Lum which gave me a great mono. But my RGB is only 6 x 4 min each and not enough to allow good clean colors. I plan on another hour at least for each channel. But still good considering I have 200,000 porch lights only a few miles to my north http://www.astrobin.com/55315/C/

      Dean

      From: Mark Striebeck
      Sent: Friday, September 06, 2013 1:23 AM
      To: ccd-newastro@yahoogroups.com
      Subject: [ccd-newastro] Removing background noise



      I continue to fight with the background noise (imaging from downtown San Jose). Even when I'm narrowband imaging. Most times, I end up clipping the image :-(

      I know that others on this list also image from light polluted areas. What techniques are you using to get rid of the noise?

      MarkS

      [Non-text portions of this message have been removed]


    • Tim Stone
      Mark, in nebulae where SII is not abundant, it results in a very low signal to noise ratio which must be accounted for. You can either take lot of subs, or
      Message 43 of 43 , Sep 22, 2013
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        Mark, in nebulae where SII is not abundant, it results in a very low signal to noise ratio which must be accounted for. You can either take lot of subs, or take longer exposures. Both approaches have their challenges. If you lengthen the exposure to get decent S/N ratio, you might have trouble with "overexposing" Ha, but a lot of subs can take a long time... Some of us just software noise reduce the heck out of the SII channel, but that can get ugly too... I'm always interested to learn how others deal with this.

        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        Tim Stone


        On Sun, Sep 22, 2013 at 11:53 AM, Mark Striebeck <mark.striebeck@...> wrote:
         

        So, I spent the last couple of nights to work on this:
        • Took 50 dark subframes to create a new master
        • Did 30 min exposures (which created new guiding challenges)
        • Dithered
        Overall, the results are great:

        I very much like the Ha and OIII stacked image - lots of detail and very little background noise. Only the SII image still looks noisy. I took these images over several nights, so there is the chance that the nights when I took the SII images had worse conditions then the others. Or is there something about SII that makes it more susceptible to light pollution or suboptimal seeing conditions?

        Thanks for all the help!!!

              MarkS


        On Wed, Sep 11, 2013 at 2:17 AM, <neil.hankey@...> wrote:
         

        I'm already doing this for a long time now. I certainly don't indeed to waste any of the precious clear nights taking DARKS and BIAS frames. The refrigerator is perfect for this, especial since we have two and one of them is in the utility room.


        I have have a video up on the youtube channel demonstrating this (insideastron0my). Thats a Zero in the name where the last 'o' should be...


        Clear Skies



        Neil.

        www.insideastronomy.com

        Hint for easily taking many darks: 

         

        Place the camera in a refrigerator and close the door.  This is a cool dark place that approximates night conditions (except some Southern summer sites <g>)

         

        Most astro cameras are NOT fully light tight and care must be taken when shooting darks in the daytime.

         

        Stan



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