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Re: manual rotator options?

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  • Mike Dodd
    ... Hi, Daniele. I understand your space restrictions. My only remaining question is, can you put an extension tube between the OTA rear cell and the camera
    Message 1 of 10 , Sep 4, 2013
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      daniele malleo wrote:
      > Mostly I'm
      > concerned about making the rotator fit in my optical train, and I
      > figured a non-motorized unit might be a little nimbler. Currently I
      > have Celestron EdgeHD 8" SCT --> SXV-AO-LF --> QSI583 WSG. Because of
      > backfocus considerations, I can only place the rotator between the
      > SCT and the AO, where really there isn't much space:
      > https://dl.dropboxusercontent.com/u/8823779/photo.JPG

      > If I read the diagram on the pyxis manual
      > correctly (page 10), the pyxis 2" is 5.79" in diameter and 1.68" deep
      > (i.e. 42mm). I would imagine mine isn't an unusual scenario (my
      > equipment is hardly exotic), so I wonder if a solution for me is out
      > there. Thanks for the input!

      Hi, Daniele.

      I understand your space restrictions. My only remaining question is, can
      you put an extension tube between the OTA rear cell and the camera
      provide more clearance for a rotator?

      I'm not familiar with the 8" EdgeHD, but I once had a C9.25 with an IFW
      filter wheel, a TCF crayford focuser, _and_ a Pyxis rotator between the
      rear cell and an ST-8 camera. See
      <http://astronomy.mdodd.com/files/cge_imaging.jpg>

      Even with the camera that far away, I was able to achieve focus. The
      mirror had plenty of range.

      I notice you have an SCT/T-thread adapter between the OTA and the
      camera. Would a longer one help? This one is 55mm long.
      <http://agenaastro.com/antares-sct-t-thread-adapter-55.html>

      This 1/2"-long SCT extension tube screws onto the SCT rear cell, and has
      male SCT threads on the other end.
      <http://www.scopestuff.com/ss_scet.htm> Maybe you could stack one or
      more of these to move the equipment back from the focuser.

      Also search for a T-thread male/female extension tube.

      I think that moving the camera back a couple of inches would let you use
      a Pyxis or other motorized rotator. You just have to figure out how to
      do it, and there appear to be several options.

      Hope this helps.
      --
      Mike

      Mike Dodd
      http://astronomy.mdodd.com
      Louisa County, Virginia USA N37.58.23 W77.56.24
    • daniele malleo
      Mike (and all who pitched in), your input is very valuable, thanks. This is my current setup (pardon the horrible quality, my garage is poorly lit):
      Message 2 of 10 , Sep 4, 2013
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        Mike (and all who pitched in), your input is very valuable, thanks.

        This is my current setup (pardon the horrible quality, my garage is poorly lit): https://dl.dropboxusercontent.com/u/8823779/opticaltrain.jpg

        I could place the rotator at the end of the T-thread adapter (and then follow with AO and camera) but that would push the CCD plane way beyond the recommended distance. Celestron recommends 133.35mm (or 5.25"), and I'm already 20mm over, at 155mm. 
        My current CCD sensor is a small one (KAF-8300), at just 22.5mm diagonal, so I haven't noticed much degradation - but this graph (http://downloads.celestron.com/KB_images/EdgeHD11-backfocus-vs-spotsize.pdf) although published for the 11" OTA would suggest pretty punishing penalties for pushing the sensor another 2" past the optimal distance.

        I suppose I could simply test the degradation by placing a 2" tube where rotator would sit  and decide whether the results are acceptable or not.

        In the meantime I have ordered the manual rotator ring suggested by Mark Striebeck, and will test that out too...


        Thanks,
        Daniele




        Hi, Daniele.

        I understand your space restrictions. My only remaining question is, can 
        you put an extension tube between the OTA rear cell and the camera 
        provide more clearance for a rotator?

        I'm not familiar with the 8" EdgeHD, but I once had a C9.25 with an IFW 
        filter wheel, a TCF crayford focuser, _and_ a Pyxis rotator between the 
        rear cell and an ST-8 camera. See 
        <http://astronomy.mdodd.com/files/cge_imaging.jpg>

        Even with the camera that far away, I was able to achieve focus. The 
        mirror had plenty of range.

        I notice you have an SCT/T-thread adapter between the OTA and the 
        camera. Would a longer one help? This one is 55mm long. 
        <http://agenaastro.com/antares-sct-t-thread-adapter-55.html>

        This 1/2"-long SCT extension tube screws onto the SCT rear cell, and has 
        male SCT threads on the other end. 
        <http://www.scopestuff.com/ss_scet.htm> Maybe you could stack one or 
        more of these to move the equipment back from the focuser.

        Also search for a T-thread male/female extension tube.

        I think that moving the camera back a couple of inches would let you use 
        a Pyxis or other motorized rotator. You just have to figure out how to 
        do it, and there appear to be several options.

        Hope this helps.
        -- 
        Mike

        Mike Dodd
        http://astronomy.mdodd.com
        Louisa County, Virginia USA N37.58.23 W77.56.24
      • Mike Dodd
        ... I think testing would be worthwhile. My ST-8 has a slightly smaller chip than yours, but at one time it was installed on an AO-7 -- the one with the
        Message 3 of 10 , Sep 5, 2013
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          daniele malleo wrote:
          > This is my current setup: <https://dl.dropboxusercontent.com/u/8823779/opticaltrain.jpg>
          >
          > I could place the rotator at the end of the T-thread adapter (and then
          > follow with AO and camera) but that would push the CCD plane way beyond
          > the recommended distance. Celestron recommends 133.35mm (or 5.25"), and
          > I'm already 20mm over, at 155mm.

          > I suppose I could simply test the degradation by placing a 2" tube where
          > rotator would sit and decide whether the results are acceptable or not.

          I think testing would be worthwhile.

          My ST-8 has a slightly smaller chip than yours, but at one time it was
          installed on an AO-7 -- the one with the mirror, where the camera was
          orthogonal to the OTA axis.

          The info on this image shows a lot of stuff in the optical path:
          <http://astronomy.mdodd.com/galaxies-08.html> It lists the IFW filter
          wheel, the TCF focuser, _and_ the Pyxis rotator, all in front of the AO-7!

          That's quite a distance from the C9.25 rear cell to the CCD chip. Stars
          are slightly elongated at the corners, but not too bad for my purposes.

          Hope this helps.

          --
          Mike

          Mike Dodd
          http://astronomy.mdodd.com
          Louisa County, Virginia USA N37.58.23 W77.56.24
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