Optical Alignment
Strap the empty tube in its saddle and clamp that to the workbench so that it cannot be moved. Set up a lamp or other light source about 48" from the eyepiece end of
the tube, and on its extended axis. Then stand a white cardboard screen, having a 1/8" hole in it, directly in front of the lamp. Make two cardboard disks, each with a 1/8" center hole, and fit one into each end of the tube. By sighting through the holes, adjust screen and lamp to bring all three holes in line.
Into each end of the adapter tube fit a wooden plug with a 1/8" center hole. Then a length of 1/8" rod is inserted through the holes in the plugs. Square the rod exactly with the tube longitudinally by means of the spring adjustments on the blocks, checking with a square and rule or dividers. Then push the rod in until it has gone past the center of the telescope tube, and, by sighting through the end of the tube, see if the rod has cut off the light.
The adapter must be adjusted until the light is cut off by the rod, then again square the rod with the tube longitudinally, as this first adjustment will no doubt have been disturbed.
Repeat the tests until you are certain that the adapter is square in both planes, after which remove the rod and plugs from the adapter, and also take the cardboard disk from that end of the telescope tube. Now put in the spider, being careful not to
disturb the position of the tube, and center it by sighting through the other end of the tube. When the spider is centered, remove the diaphragm from the mirror end and put in the cell containing the mirror. An image of the hole in the cardboard screen will probably be seen somewhere on the screen, and by manipulating the adjusting nuts on the cell make this image fall directly back on the hole. The axes of tube and mirror have now been made coincident and at right angles to the axis of the adapter tube.
All that remains is to insert the diagonal and to bring the deflected axis of the mirror coincident with the axis of the adapter. Fix a small diaphragm of some sort, having a 1/16" hole at its center, over the eyepiece end of the adapter. Placing your eye
close to this opening, you will see the walls of the adapter tube, a reflection of the mirror in the diagonal, and in this a reflection of the spider and diagonal, and also a reflection of the hole through which you are peering. These reflections must all be brought concentric with each other, and if the preliminary work has been carefully done, the three adjustments that are provided on the diagonal will be sufficient for the purpose. This last operation is most easily performed outdoors with the telescope pointed at the daylight sky.
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