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Collimating a Newtonian Refractor Telescope

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  • keithhfinelli
    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
    Message 1 of 3 , Jan 4, 2013
      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.
    • 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 2 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 3 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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