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Re: SCT eastward drift

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  • Mike Dodd
    ... Two questions: 1. Once it starts drifting eastward does it continue drifting forever, where does the drift eventually stop? 2. Does the drift occur
    Message 1 of 3 , May 31, 2009
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      alex wrote:
      > I posted this on other forums but no replies so far...I have an SCT
      > scope on the wedge drift aligned (no star movement for at least 5
      > minutes due south or west), however when I am trying to image an
      > object due north about 50 degrees declination everything starts to
      > drift eastward within 30 seconds.

      Two questions:

      1. Once it starts drifting eastward does it continue drifting forever,
      where does the drift eventually stop?

      2. Does the drift occur regardless of which way you slew to the target,
      or does it occur only if you slew eastward?

      Is the answer to #1 is that the drift eventually stops, and the answer
      to #2 is that the drift occurs only after an eastward slew, it sounds to
      me like the problem is lash in the RA drive. After an eastward slew, the
      RA drive motor spends its time winding out the lash, and the mount does
      not move westward until the lash is completely wound-out.

      Just a theory, but I've seen this behavior on two mounts I've owned.
      Hope this helps.

      Mike
      -----

      Mike Dodd
      Montpelier, VA USA
      http://astronomy.mdodd.com
    • JoeMize
      Alex, as someone has already mention you might be seeing the classic SCT Mirror Flop even if it is locked down. Bust since you use a Tripod I m wondering if
      Message 2 of 3 , Jun 1, 2009
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        Alex, as someone has already mention you might be seeing the classic SCT
        Mirror Flop even if it is locked down. Bust since you use a Tripod I'm
        wondering if you've tested your tripod/wedge?

        Orient your camera exactly E-W by taking very short images continuously
        while adjusting the camera's orientation so a star follows the E-W line of
        the crosshairs on the image as you manually move the star with your
        handcontroller.

        Next point your SCT to the area where you see drifting, now turn off the
        drive and make a 5-10mins test image. If you're correctly polar aligned the
        stars will make straight lines along the E-W crosshairs. Wait 15-20mins and
        try again. If the stars now don't follow the crosshair lines there's
        slippage of the wedge or tripod, maybe the tripod is sinking into the
        ground...joe :)


        "May You Go Among The Imperishable Stars"
        Joe Mize www.cav-sfo.com
        Chiefland Astronomy Village, Fla.

        ----- Original Message -----
        From: "alex" <shurik0001@...>
        To: <undisclosed recipients:>
        Sent: Sunday, May 31, 2009 5:04 PM
        Subject: [ccd-newastro] SCT eastward drift


        >
        > I posted this on other forums but no replies so far...I have an SCT scope
        > on the wedge drift aligned (no star movement for at least 5 minutes due
        > south or west), however when I am trying to image an object due north
        > about 50 degrees declination everything starts to drift eastward within 30
        > seconds.
        >
        > Scope is balanced on all axes and tripod is leveled.
        >
        > Any ideas what is causing this and how to fix it ??
        >
        > thanks, Alex
        >
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