Finish instrument assembly

 To finish assembling the instrument, feed the clear plastic nitrogen tube through the cable boot box and fit it over the plastic nozzle-like connector on the etalon. The tube should have a pair of small nuts near the etalon end of the hose; these serve to block light where the hose enters the boot box. Then disconnect the tube a couple of feet from the etalon, so that when you eventually turn on the nitrogen, dust in the tube is not blown into the etalon.

  

Figure 12: A close-up of the cable boot box installed on the side of the Fabry-Perot instrument tube. The etalon cable and nitrogen hose emerge from two holes in the cover panels on the front of the box. A piece of black tape covers up the hole between the cable and the hose.

Next, attach the small cable boot box to the Fabry-Perot tube with four small hex screws, enclosing the etalon cables and nitrogen hose. Attach the two small cover panels to the front of the boot box with four very small hex screws. The anodized ring and rubber insert on the etalon cable should slip into the large hole between the panels, while the nuts on the nitrogen tube should slip into a smaller hole. You may have to push a slight amount of cable into the boot box to get the cover panels in place; the ensures against excessive strain on the etalon connections. There is an additional small hole in the joint between the cover panels; it, as well as any other gaps, should be covered with black tape to reduce light leakage. The end result should look like Figure 12.