Install calibration filter

 The easiest way to verify the operation and parallelism of the etalon is through observations of a (usually Neon) calibration lamp, since it will provide a large number of sharp, bright emission lines. For the usual case of the Neon calibration source, the 6593Å interference filter should be installed in the filter wheel, in order to isolate the relatively strong 6598.95Å Neon line. The filter is a 3-inch square filter and can be found in the small wooden box marked ``Narrow-band Filters'', in the Palomar 60-inch observing floor equipment closet. If you are observing at the 200-inch telescope, this filter box may not have been brought over from the 60-inch dome; if so, you will need to retrieve it.

Be careful not to touch the surface of the filter. Before installing it, you may want to clean any dust off with dry nitrogen or a lens brush. Filter installation is slightly different between the two telescopes:

• 60-inch
  The filters should be left in their holders, since the 60-inch filter wheel contains slots for 3-inch square filters. First, a small access cover must be removed on the north side of the filter wheel, by loosening a pair of hand-tight screws. Each filter is then slid into one of the 12 spaces available on the wheel, using the spring-loaded pin to hold it in place. The wheel may be rotated manually using the knob on the filter wheel motor drive. Ask the Palomar crew to assist you in this procedure, should you have any questions. The reflective side of each filter should be oriented away from the instrument, i.e., towards the sky. Be sure to note the slot in which the filter has been installed. Verify that the filter wheel can be turned without catching on the filter, then replace the access cover.

• 200-inch
  The F/9 guider base contains the filter wheel for use at the 200-inch telescope. However, this filter wheel was designed for 2-inch square filters. A pair of 3-inch square filter holders have therefore been fabricated for use with the Fabry-Perot; these are kept in a small plastic bag. Each filter must be carefully removed from its current holder and fastened into one of these special holders, using a pair of the small white plastic screws also found in the plastic bag. See Figure 15. Be very careful not to touch, scratch, or otherwise damage the filter while transferring it to the alternate holder. The reflective side of each filter should be oriented face-up in the holders.

  
  

    

  Figure 15: The special filter holders used for mounting 3-inch square filters in the F/9 base filter wheel on the 200-inch telescope. Clockwise from the lower left are the standard filter holder, the lid for the standard holder, the 4 small screws and rubber stoppers from the standard holder, the filter resting in the special F/9 base filter holder, and one of the pair of white plastic screws used for fastening the filter into the special holder.

  
  
  

  Filters are installed in the F/9 guider base by lifting them through a small access hole just west of the telescope optical axis (see Figure 7). The filter holder is fastened into the F/9 base by a set of three screws integrated into the holder. Again, be careful not to damage the filter while screwing the holder into place above your head. Note the slot in which the filter has been installed.

Although you may be tempted to install other filters as well, it is recommended that you install only the calibration filter at this time, in order to expedite the setup process. However, since calibration lamp exposures are usually made throughout the course of observations, as a standard measure of the etalon response, you should install the calibration filter in a slot in which it may remain for the duration of the observing run.