Mount instrument on telescope

 Before mounting the instrument on the telescope, it is useful to lay the Fabry-Perot on its side and look through the optical path. Remove the cardboard covers on the field lens end of the instrument and on the outside of the dewar plate. Using a flashlight if necessary, confirm that the optical path is clear.

  

Figure 7: The Fabry-Perot instrument, as it appears mounted on the 200-inch telescope. Note the 45° angle between the F/9 base and the Fabry-Perot mounting plate. Visible near the filter access hole is the mounting bolt that has been relocated for use at the 200-inch telescope.

The Fabry-Perot mounts on the telescope with four large bolts. These bolts attach through the holes in the base plate of the instrument, into the corresponding holes in the base of the telescope. On the 60-inch telescope, there are two possible orientations for the instrument; it is usually mounted on the telescope such that the etalon cable connectors are on the north side of the instrument. On the 200-inch telescope, one bolt hole has been shifted to accommodate the F/9 guider base, and the instrument therefore has only a single possible orientation (see Figure 7). This is not a real limitation, since the 200-inch telescope has a ring by which the entire instrument base can be rotated. It's best to have three people to help mount the instrument on the telescope - two to hold the instrument and one to fasten the bolts. Inserting two bolts in opposite corners with your fingers should be enough to hold the instrument in place while you insert the rest of the bolts. Make sure all of the bolts are thoroughly tightened.