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[William Optics] Re: Is anyone using an FLT-132 with a QSI-583wsg camera and Orion SSAG Autoguider?

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  • Bazarov
    My first reaction upon discovering the disparity between the quality of the SSAG images seen through the autoguider port, versus those obtained via the guide
    Message 1 of 4 , Mar 1, 2010
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      My first reaction upon discovering the disparity between the quality of the SSAG images seen through the autoguider port, versus those obtained via the guide scope, was similar to your thought; but I found out that people using the QSI-583wsg with other scopes (e.g. Takahashi FSQ-106) are getting much better results than I. It seems likely to me that the pickoff prism of the 583wsg is too far off at the periphery of the light cone coming through the field flattener. That is what the folks at QSI have suggested. Although I have arranged to borrow a Starlight Express Lodestar next time out from the aforementioned Takahashi owner to see whether a better autoguider will improve the view, I'm inclined to think it won't help much and that I'll be stuck with using the autoguider with the guide scope. Anyway, thanks to the people who responded to my post; best regards and clear skies to everyone.

      --- In William-Optics@yahoogroups.com, "Astro Huyps" <astro@...> wrote:
      >
      > Perhaps the explanation is simply that an off-axis guider only picks-up a fraction of the total light via the intercepting prism; the rest of the light is going to the main camera; In case you have a dedicated guide scope, all the light of the guide scope is going to the autoguider. The focal length (and the focal ratio) of the guide scope versus the main scope is I think only a secondary effect.
      >
      > regs
      > Ronald
      >
      >
      >
      > ----- Original Message -----
      > From: mackey
      > To: William-Optics@yahoogroups.com
      > Sent: Monday, February 22, 2010 12:03 PM
      > Subject: [William Optics] Re: Is anyone using an FLT-132 with a QSI-583wsg camera and Orion SSAG Autoguider?
      >
      >
      >
      >
      >
      > --- In William-Optics@yahoogroups.com, "Bazarov" <jlfloyd@> wrote:
      > >
      > > This is because only the brightest stars show up in the autoguider
      > > when it is mounted in the guide port; others are too faint to be
      > >recognized as guide stars or are not visible at all. However, when I
      > >remove the Orion SSAG from the QSI guide port and install it in a
      > >guide scope mounted on top of the FLT-132, star images are much
      > >brighter and more distinct, more stars show up, the SSAG has no
      > >trouble acquiring guide stars and calibration is generally successful.
      >
      > I *assume* that the focal length of your guide scope is shorter
      > than that of FLT-132 which has a focal length of 921mm.
      >
      > 921mm is quite long and it *distributes* the star image over
      > a larger area than the guide scope does. It means that each pixel
      > of Orion SSAG gets less light. Also a long focal length scope
      > simply gives your guide chip *smaller* field of view, which
      > usually means less bright stars.
      >
      > Orion SSAG is not a very sensitive guiding CCD, the same as
      > QHY5. I'd suggest you try a more sensitive guiding camera, like
      > Fishcamp Starfish. It is *much* more sensitive than QHY5.
      >
      > Hojong Lin
      >
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