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25167Re: H-alpha filters

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  • Don Goldman
    Mar 17, 2004
      I just wanted to mention that Astrodon Tru-Balance H-a filter is
      parfocal with the LRGBs and unblocked clear filters. It was designed
      at 6 nm FWHM, but provides ~90% optical throughput. The key for me
      was to provide an H-a filter that did not require a focus change.

      BTW, I have comparisons on my web site of the 9.5 nm (Schuler) vs the
      original 3.5 nm FWHM (Custom Scientific) H-a alpha in the emission
      filter page. In this FWHM range, I do not see any deleterious impact
      of the wider 9.5 nm filter letting more broadband light in other than
      the aesthetic issue of more and brighter/fatter stars that are
      actually a better match to the RGBs. Have you tried blending in H-a
      into the RGBs and see a tiny white bullet inside a larger colored
      star? The S/N is higher for the Schuler because it's throughtput is
      80% compared to 72% for the narrow 3.5 nm CS H-a. The S/N
      improvement simply comes from the throughput. Now, people have a
      choice between the more recent SBIG/CS 10 and 4.5 nm H-a filters and
      my Tru-Balance H-a that all have ~90% throughput.

      Don Goldman
      Tru-Balance Filters
      www.astrodon.com




      --- In ccd-newastro@yahoogroups.com, "Ron Wodaski" <ronw@n...> wrote:
      > 1. Yes, this is normal. The Ha filter is a pretty thick sandwich,
      and cannot
      > be parfocal with thinner, simpler filters.
      >
      > 2. I occasionally can find a guide star, but I use a guidescope
      because it's
      > much more flexible with an Ha filter.
      >
      > Ron Wodaski
      > author of The New CCD Astronomy
      > http://www.newastro.com
      >
      > -----Original Message-----
      > From: remi lacasse [mailto:rmi.lacasse@s...]
      > Sent: Monday, April 01, 2002 6:57 AM
      > To: ccd Newastro; SBIG user group
      > Subject: [ccd-newastro] H-alpha filters
      >
      >
      > Hi,
      > A few months ago I received my H-alpha filter from SBIG.
      > It is the Standard type and I would like to ask 2 questions to
      > the group or to those who have used the same type filter before:
      > - I am using an ST-10E with the filter installed in the empty slot
      > of the CFW-8 but the focus point is very different from the
      > other filters. Is this normal?
      > - Is it possible to use (find) a guide star and if so what is the
      minimum
      > magnitude through the filter? Or will I need an external way to
      guide
      > when using the filter?
      > Thanks in advance
      > Remi
      > RĂ©mi Lacasse et/ou Lise Charlebois
      > Observatoire"MIRABILIS"
      > Lat. 46 deg.
      > Long. 74 deg.
      >
      >
      >
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