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Re: C9.25 to a C11

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  • Roger Hamlett
    ... Er. Area og 11 primary = pi* (5.5^2) = 95 square inches. Area of 9.25 primary = 67 square inches. Increase is over 41% (actually very slightly more,
    Message 1 of 9 , Sep 1, 2004
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      > Assuming the same optical performance the C11 should
      > gather 2.419354838709% more light, but still not get
      > you to magnitude 15. What's the additonal cost and
      > weight penalty to get those additional photons?
      >
      > =====
      >
      > Geo. Cushing, Delanson, NY, US
      >
      > http://www.georgecushing.net
      Er. Area og 11" primary = pi* (5.5^2) = 95 square inches. Area of 9.25"
      primary = 67 square inches. Increase is over 41% (actually very slightly
      more, since the secondary on the 9.25, is a little larger in proportion,
      than the one on the 11" scope). The 'plus' of the 9.25, is that it has a
      flatter field. However to get this, it is heavier for it's size (and
      longer), than a 'normal' SCT. The 11", only weighs about 7lbs more than the
      9.25.
      Remember 'magnitudes', use a logarithmic scale. It takes a change in light
      gathering power, of 251%, to gain one magnitude. So the change in limiting
      magnitude quoted for the scopes (0.3 mag), is a much larger change than it
      may appear.

      Best Wishes
    • gnowellsct
      Actually what is important is whichever is bigger, the CO or the hole in the primary. The celestron line of scts is not consistent on this point. I actually
      Message 2 of 9 , Sep 1, 2004
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        Actually what is important is whichever is bigger, the CO or the hole
        in the primary. The celestron line of scts is not consistent on
        this point. I actually have the data in a spreadsheet and have been
        meaning to post it to the files section.

        I'll try to get to that.


        regards Greg N


        --- In sct-user@yahoogroups.com, "David" <Ginahoy@a...> wrote:

        > Although this isn't necessarily the size of the hole
        > in the primary (which is really what's important for
        > your question), the difference is small and the
        > proportions similar.
        >

        > David Butler
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