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RE: [Telescopes] Collimating a Newtonian Refractor Telescope

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  • Julian Shull
    Is what you are calling a collimating cap a Cheshire eyepiece of something similar with a small hole centered on a bore scope built into a 1.25 eyepiece?
    Message 1 of 3 , Jan 4, 2013
      Is what you are calling a "collimating cap" a Cheshire eyepiece of something
      similar with a small hole centered on a bore scope built into a 1.25"
      eyepiece? That would be the correct tool. This tool should snugly fit into
      the focuser and not have any appreciable play. If not, wrap a few turns of
      electrical tape around it until it is snug and repeat the process.



      In addition to adjusting the pitch of the secondary mirror with the 3
      collimation screws, you may need to center the secondary on the eyepiece by
      moving all 3 screws in or out together. Also, you need to make sure the
      focuser is perpendicular to the optical path. This is done by carefully
      measuring the center of the focuser and making a mark on the opposite wall
      of the tube/secondary cage the same distance. This should be as exact as you
      can make it. Then use the bore scope or Cheshire and level the focuser with
      its leveling screws (or add shims if there are no screws) to center the
      mark. THEN begin the rest of the collimation.



      Collimation is very important to the basic performance of a telescope. If
      you have great optics, they will not perform if you are not in good
      collimation. The faster the optics, the more critical this becomes.



      JS in BC



      _____

      From: telescopes@yahoogroups.com [mailto:telescopes@yahoogroups.com] On
      Behalf Of keithhfinelli
      Sent: Friday, January 04, 2013 3:08 PM
      To: telescopes@yahoogroups.com
      Subject: [Telescopes] Collimating a Newtonian Refractor Telescope





      Im having a slight issue with getting the Secondary mirror lined up. I have
      all steps correct (I think). The main issue is when looking through the
      viewer with a collimating cap in place. The mirrors are slightly off in that
      I cannot see all 3 points that are around the circumference of the mirrors.
      When I adjust it with the screwdriver I can get all 3 in the viewer but when
      I adjust the cap viewer to be centered, it moves it to where only 2 of the
      points are in the viewer. This is the only issue Im having. Is this going to
      cause a major problem? Will it just take finesse on my part to get it right?
      Should I take it somehwere? Or is this a non issue to worry about.

      Any help would be greatly appreciated.

      Its not far off center just enough to not see all 3 points. I hope you know
      to what Im referring when I mention these parts.





      [Non-text portions of this message have been removed]
    • Geoff Gaherty
      ... 1. Make sure the focuser is square to the tube by removing the secondary, marking the spot directly opposite the focuser, and sighting through the focuser.
      Message 2 of 3 , Jan 4, 2013
        On 04/01/13 6:07 PM, keithhfinelli wrote:
        > Im having a slight issue with getting the Secondary mirror lined up.
        > I have all steps correct (I think). The main issue is when looking
        > through the viewer with a collimating cap in place. The mirrors are
        > slightly off in that I cannot see all 3 points that are around the
        > circumference of the mirrors. When I adjust it with the screwdriver
        > I can get all 3 in the viewer but when I adjust the cap viewer to be
        > centered, it moves it to where only 2 of the points are in the
        > viewer. This is the only issue Im having. Is this going to cause a
        > major problem? Will it just take finesse on my part to get it right?
        > Should I take it somehwere? Or is this a non issue to worry about.
        >
        > Any help would be greatly appreciated.
        >
        > Its not far off center just enough to not see all 3 points. I hope
        > you know to what Im referring when I mention these parts.

        1. Make sure the focuser is square to the tube by removing the
        secondary, marking the spot directly opposite the focuser, and sighting
        through the focuser. A crosshair collimator like Orion's helps.

        2. Make sure the secondary is directly under the focuser by adjusting
        its position.

        3. Make sure the primary is centred in the secondary by adjusting the
        secondary (in and out, then tilt). This is where you should see all
        three mirror clips.

        4. Adjust the primary so that the secondary is centred on it. Again a
        crosshair in the collimator helps, as does a centre spot on the primary.

        5. Go back to step 2, and repeat the sequence until all is concentric.

        There are good instructions here:

        http://www.backyardastronomy.com/Backyard_Astronomy/Chapter_15__Polar_Alignment,_Collimation,_Cleaning_and_Testing_of_Telescopes_files/Appendix%20B-Collimation.pdf

        Geoff

        --
        Geoff Gaherty
        Foxmead Observatory
        Coldwater, Ontario, Canada
        http://www.gaherty.ca
        http://starrynightskyevents.blogspot.com/
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