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To collimate the telescope (see attachment Coll1.jpg):

1) Set the sextant at zero and lay it down so the frame is horizontal.

2) Place a sighting vane (diopter)each end of the arc parallel to the axis of 
the telescope at about 0 and 120 degrees and look at a distant (<1000 
metres) object so that the object and the tops of both vanes coincide. Better 
still, align them with a distant horizon. Wedge the sextant as necessary to 
align with  the object. 

3) Look through the x 6 telescope. The chosen object should be in the centre 
of the field in the vertical axis. If it is not, make it so by using the 
adjusting screws.

Do not overtighten the screws. The telescope mount is easily distorted.

This is a fundamental method that does not need any measuring.


To place the index mirror perpendicular to the frame (see attachment Perp3 jpg)):

1) With the instrument horizontal, set the index arm to about 40 degrees

2) Place a vane at 0 and 120 degrees, so that they face the axis of the instrument.

2) Look past the lower (right) edge of the index mirror at the vane set at 
zero. You should be able to see the other vane reflected in the mirror at the 
lower right) edge. You may need to adjust the position of the index arm 
slightly. The tops of direct and reflected images should be in a straight 
line. If they are not, make them so.

If you have your eye 80 to 100 mm from the mirror, the line appears to be 
continuous through the frame of the mirror. This method makes the adjustment 
at the approximate height of the viewing axis of the instrument though is of 
no importance when the apparent reflective surface of the index mirror lies 
on the axis of the index arm. Even when it does not, as in instruments like 
the SNO-T, which has a first surface mirror, the error is small, as long as 
you view the images close to the plane of the frame.

Bill Morris
Pukenui
New Zealand
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