Install camera and dewar plates

 To prepare to install the camera lens and dewar plates, remove the plastic cover from the top side of the etalon, using the metric hex wrench. Be sure to return the wrench to the ET-50 etalon box afterwards. Remove the camera lens cap. Using dry nitrogen, blow off the upper surface of the etalon and the camera lens. (You may then turn off the nitrogen flow.) Check one more time that the camera lens aperture has been set all the way open.

Lift the camera plate and attached lens, flip it over, and align it on the end of the instrument tube. If you are using the internal shutter, reach in and thread the cable from the shutter through the small (~1-inch) round hole in the tube. As you lower the camera lens plate onto the tube, you will have to tip it slightly, so that the arm of the camera focus ring fits into the small slot in the side of the tube. There is also a guide pin in the camera lens plate that must mate with its guide hole in the instrument tube or extension ring. You may have to rotate the position of the camera lens in the bayonet mount, in order for the arm of the focus ring to align with its slot, the guide pin to align with its hole, and the screw holes in the camera lens plate to align with those in the end of the instrument tube or extension ring. It may take some effort to get this right. See Figure 5 for an illustration.

  

Figure 5: The camera plate being installed on the end of the Fabry-Perot instrument tube. Note the focus ring arm and the slot into which it must be aligned, below the extension ring. There is also a guide pin on the camera plate which must be mated to its hole in the extension ring.

When the camera lens plate is properly in place, position the dewar plate on top of the camera lens plate, and attach both tightly to the instrument tube, using the six long silver hex screws. There is no preferred orientation for the dewar plate. Make sure that the camera lens and dewar plates are flush together, with no tape or other obstruction between them.

Finally, attach the small curved focus plate to the slightly protruding end of the camera lens focus arm, using the two tiny hex screws. You should then be able to adjust the camera lens focus by sliding this plate along the outer surface of the instrument tube. It should not be so loose as to allow light leaks. You probably do not need to attach the small guide screw in the focus plate. Set the focus lever to the middle of its range of movement.

  

Figure 6: The assembled Fabry-Perot instrument tube, just prior to its mounting on the telescope. Note the installed etalon, extension ring, camera plate, and dewar plate. Note also the shutter control cable, which has been threaded through a small round hole in the tube.

The assembled instrument should resemble that seen in Figure 6, with the possible exception of the shutter cable, which will not be present at the 60-inch telescope.