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     6.  Slide the light-path marker for the secondary fixture until it is at the calculated distance from the mirror-marker (center of secondary).

     With the rod of the primary fixture passing through the centerline of the light-path running from the secondary mirror to the focal point and passing directly in front of the center of the primary, the principal plane of the optical system is now defined by this rod (a straight line) and the center of the secondary mirror (a point).

     7.  While sighting along the centerline of the eyepiece tube adjust the three collimating screws on the secondary mirror mount until the light-path marker on the eyepiece axis and the two mirror-markers appear to fall one behind the other on a single straight line. When this has been accomplished, the secondary mirror has been adjusted to the proper tilt-angle and its tilt-line must be accurately perpendicular to the principal plane.

     8.  Rotate secondary fixture about the axis of the secondary mirror until secondary rod appears to be parallel to - and lie on top of - the primary fixture rod. This then places the light-path marker of the secondary fixture in the principal plane of the instrument.

     9.  Adjust the three collimating screws of the primary mirror until the light-path marker of the secondary fixture appears to fall in line with the others. This, then places the primary mirror at the proper angle of tilt and leaves its tilt-line perpendicular to the principal plane. Remove both collimation fixtures from the telescope.

     10.  With the telescope pointed at a bright star high in the sky and a high-power eyepiece, adjust tension and rotation of the warping harness until a perfect star image is obtained. Follow the procedures as described under the heading of "Shop-Test of Warping Harness."