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6922Re: H-alpha filters

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  • mbendaniel
    Apr 1, 2002
      --- In ccd-newastro@y..., "remi lacasse" <rmi.lacasse@s...> wrote:
      > 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?

      Yes. It's due to different thickness of the glass.

      > - Is it possible to use (find) a guide star and if so what is the
      > magnitude through the filter? Or will I need an external way to
      > when using the filter?

      You'll need at least one of the following:
      * a very bright guide star (use TheSky or similar)
      * long guiding integrations (e.g. 10 seconds)
      * a guide scope or OAG with separate autoguider (expensive)
      * the SBIG TC-237 upgrade (expensive)
      * more aperture

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