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74060Re: [ccd-newastro] Light Pollution filter as luminance?

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  • Audie Hickey
    Apr 20, 2014
    Hi Mark,

    I use the LPS with OSC and Mono Cameras with LRGB Filters.  The only time I don't use it is when doing Narrow band work.  Lately I've been using a HyperStar with an ST10.  LRGB when the moon isn't blazing and Narrow band when it is. It is normal for me to get 9+ hours of data to use per target over many nights.  I try not to image below about 45 Degrees from Zenith.  I attached a quick auto stretched (DDP Auto in CCD Stack) image of the LUM from M33 I'm working on.  About 4 hours of LUM with ST10 and HyperStar.  Imaged in my backyard.  I probably won't stretch it this hard because I can see some artifacts from the flats starting to show.  Flats are important when you have light pollution.

    Audie
    On Sunday, April 20, 2014 6:50 PM, Ron Wodaski <rwodaski@...> wrote:
     
    You’re dealing with fundamental physics here. Signal and noise.

    Combining red, green, and blue images is going to be nearly the same as using a luminance filter - you will have about the same spectrum coming through either way. I don’t think there’s anything to be gained that way. 

    If you want to use a light pollution filter, then success depends on whether or not it filters out the specific wavelengths that are a problem for you. On the one hand, you could attempt to study the wavelengths, but that’s a sophisticated effort. You can also buy one and try it, or borrow on from a friend.

    It’s tough to get good results from a light polluted area. You needs a LOT of signal to be able to clean up the unwanted signal. There’s no tricks or secrets. It just takes a lot of time on sky and developing the skills to get rid of that unwanted signal.

    Ron Wodaski




    On Apr 20, 2014, at 5:44 PM, Mark Striebeck <mark.striebeck@...> wrote:

    Hi,

    Now, where galaxy season is upon us, I have to put my narrowband filters aside for a little and try to improve my RGB imaging skills. I am imaging from near downtown San Jose, CA. Light pollution is pretty bad!

    My main struggle is with luminance - using a luminance filter is useless under these conditions.

    I tried to do RGB imaging only (all binned 1x1). With that, I get relatively good object data, but it's hard to get out details and to reduce background noise.

    I am trying right now to create a synthetic luminance image and use that - but so far with mixed results.

    I also took some Ha subs to be used as a luminace layer (and to boost the red signal) but their SNR is still pretty bad (low background noise, but also low signal).

    I wonder if it would be possible to use a light pollution filter to take a luminance image?

    Or any other methods that people use?

         MarkS




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