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Re: Rosette median combine

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  • mjchapa@aol.com
    Hey gang, Awesome images1 I have a question about median combining. My own personal experience is I get a much better image even with f2 FASTAR imaging by
    Message 1 of 2 , Nov 30, 2000
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      Hey gang,

      Awesome images1

      I have a question about median combining.  My own personal experience is I
      get a much better image even with f2 FASTAR imaging by summing, rather than
      median combining.  This enables more DDP or other processing.  I understand
      WHY median combining is desirable to get rid of pixel issues, but WHEN should
      it be applied?  The full well of my ST-237 isn't so deep with 4000 being the
      max high res dynamic range so with the quick FASTAR I often can only take a
      1-2min luminance exposures to avoid saturating the bright stars.  The ABG in
      the chip prevents blooming 99% of the time if I go longer, but then galaxy
      cores are "burned" in and unable to be processed.  Thanks in advance for any
      help on this matter.

      Mike Chapa

      8" Celestron FASTAR SCT/G-11/ST-237 astroimaging webpage @
      http://members.aol.com/mjchapa/astroimaging/main.html
    • Ron Wodaski
      My own experience has been that median combines usually offer me the best images. I use it almost all the time. Where you might run into problems with summing
      Message 2 of 2 , Dec 1, 2000
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        My own experience has been that median combines usually offer me the best images. I use it almost all the time.
         
        Where you might run into problems with summing is when the summed values exceed the bit-depth of your image. For example, if you are saving as 16-bit FIT files, you need to stay below 65,000. You can sum a lot of images from the ST-237 before you hit that limit. But if you are using an ST7/8, with a saturation level of about 40k, summing even two images can lead to problems.
         

        Ron Wodaski
        The New Astronomy Book Site - http://www.newastro.com

        -----Original Message-----
        From: mjchapa@... [mailto:mjchapa@...]
        Sent: Thursday, November 30, 2000 7:22 PM
        To: ccd-newastro@egroups.com
        Subject: [ccd-newastro] Re: Rosette median combine

        Hey gang,

        Awesome images1

        I have a question about median combining.  My own personal experience is I
        get a much better image even with f2 FASTAR imaging by summing, rather than
        median combining.  This enables more DDP or other processing.  I understand
        WHY median combining is desirable to get rid of pixel issues, but WHEN should
        it be applied?  The full well of my ST-237 isn't so deep with 4000 being the
        max high res dynamic range so with the quick FASTAR I often can only take a
        1-2min luminance exposures to avoid saturating the bright stars.  The ABG in
        the chip prevents blooming 99% of the time if I go longer, but then galaxy
        cores are "burned" in and unable to be processed.  Thanks in advance for any
        help on this matter.

        Mike Chapa

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