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24418RE: [ccd-newastro] H-alpha filters

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  • Wodaski - Yahoo
    Mar 1, 2004
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      Both of those are fairly wide-band filters. They will let in Ha, but they
      will also let in light that is near Ha. This will reduce the contrast of the
      Ha features, and it will also make all of the stars brighter.

      Personally, I prefer a narrowband filter, maybe in the 3-5nm range. This
      cuts out other bandwidths and provides better contrast, and stars are
      greatly reduced which allows the nebula to stand out. But a narrowband
      filter comes at some cost: it also lets in somewhat less Ha, too. A narrow
      filter might allow 70-80% of the Ha through; a wider filter will allow
      80-95% through.

      To me, the drop in Ha (say from 90 to 75 on average) is well worth the drop
      in non-Ha.


      Ron Wodaski
      The New CCD Astronomy Book
      http://www.newastro.com/ipb


      -----Original Message-----
      From: David Morris [mailto:dmorris99us@...]
      Sent: Monday, March 01, 2004 8:58 AM
      To: ccd-newastro@yahoogroups.com
      Subject: [ccd-newastro] H-alpha filters

      Can anyone tell me the practical differences
      between a 10nm bandpass H-alpha filter and a 13nm
      bandpass one? What are the pros and cons, or is there
      really much difference?
      I'm imaging with an ST-8E through anything from an
      Orion Short-tube 90 to a 10" LX200.
      Thanks for any comments,
      David M.

      =====
      http://www.homestead.com/STVphotography

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