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Re: manual rotator options?

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  • daniele malleo
    Mike, I take no offense, and in fact I appreciate any advice. The reason I was thinking of a manual option wasn t cost. Mostly I m concerned about making the
    Message 1 of 10 , Sep 3, 2013
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      Mike,
      I take no offense, and in fact I appreciate any advice.
      The reason I was thinking of a manual option wasn't cost. 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
      I have about 31mm of depth available, and as can be seen in the photo, the rotator cannot be more than 4" diameter or it will collide with the microtouch focuser.
      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!
      Daniele


      > On Sep 3, 2013, at 2:33 AM, ccd-newastro@yahoogroups.com wrote:
      >
      > I don't know of one, but I suggest you reconsider a motorized rotator.
      > If the website you linked is correct, the manual Zerotator costs $895,
      > discounted. Or did the one you were thinking of cost less?
      >
      > A 2" Optec Pyxis motorized rotator lists at $925 -- only $30 more.
      >
      > I have a 2" Pyxis. There are several distinct advantages to using a
      > motorized rotator:
      >
      > 1. Precise and repeatable framing. You can rotate the camera to an exact
      > angle. If you image over multiple nights or even with an EQ mount past
      > the meridian, you can rotate it to that exact angle each time.
      >
      > 2. Simplified planning. You can rotate the camera FOV outline in TheSky
      > (for example) to frame your target there, then rotate to that angle at
      > the start of the imaging session without any hassle.
      >
      > 3. Remote control. You can use a small "control panel" app to operate a
      > motorized rotator from the same PC you're using to capture images.
      > Rotate to the initial angle, take a quick test shot to check the
      > framing, make any adjustments, then start imaging.
      >
      > 4. Future capability. If you ever decide to upgrade to automation
      > software, your motorized rotator is ready to go. Not so with a manual
      > rotator.
      >
      > I hope you're not offended by my suggesting a motorized rotator. I think
      > it is worth considering, given its benefits and the unavailability of a
      > manual rotator.
      >
      > --
      > Mike




      [Non-text portions of this message have been removed]
    • 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 2 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 3 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 4 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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