Install camera lens

 There are two camera lenses available for use in the Fabry-Perot: a 58 mm lens and a 105 mm lens. The 105 mm lens and 306 mm collimator is the most commonly used combination. The 58 mm lens should theoretically allow for a larger field of view, however the limiting factor is the optics of the instrument. The result is that the 58 mm lens simply compresses a field the same size as the 105 mm lens onto a portion of the CCD chip only half as large. Unless you are using a CCD with small pixels, e.g., 12 µm, and/or an etalon with lower resolution than the Palomar ET-50, the 58 mm lens should probably not be used. (More information is available in Appendix B and on the Fabry-Perot instrument web page.) Table 2 gives the relevant statistics for the 105 mm lens with the two available collimators.

   

18.9 43.3

First place the camera focus ring on the camera lens. This ring and its attached arm are used to control the focus of the camera lens from outside of the assembled instrument. Note that there is a different ring for each lens: the focus ring for the 58 mm lens has a bend in its arm; the focus ring for the 105 mm lens has a straight arm. The ring should press down firmly, seating around the lens over the rubber grip ring. You may adjust the small screw in the ring to tighten or loosen the ring as necessary. The focus ring should be flipped such that its arm attaches to the side of the ring closest to the bayonet mount on the camera lens. If the ring is installed upside down, you will not be able to insert the mounted lens and camera plate onto the end of the instrument - the arm of the focus ring will not protrude from the tube in the proper position.

  

Figure 4: The proper orientation of the camera lens focus arm on the 105 mm camera lens. The left panel illustrates the proper position for the focus arm with CCD #15, i.e., with the left edge aligned on the ``70 foot'' focus indicator. The right panel illustrates the proper position for the focus arm with CCD #16, i.e., with the left edge aligned on the ``30 foot'' mark.

The exact position of the ring on the camera lens is crucial, in order that the allowed range of focus on the final assembled instrument will include the position for the best camera focus. For the case of the 105 mm lens and CCD #15, the ring should be installed such that the left edge of the arm is centered over the ``70'' on the lens focus scale. For the case of the 105 mm lens and CCD #16, the positioning is slightly different (see Figure 4).

After the arm has been properly positioned, fasten the camera lens to the inner side of the camera lens plate, using the bayonet mount. If the camera lens is properly mounted, the focus ring arm will align roughly with the pen markings on the inner face of the camera lens plate. These markings indicate the position of the slot in the instrument tube for the focus arm; it is close to the position of the guide pin on the camera plate. Next look through the lens, open the shutter if necessary, and adjust the camera lens F/stop to the lowest setting, so that the aperture is all the way open. Check again to verify that the lens is securely affixed in the bayonet mount. Leave the lens cap on the camera lens during the next step, for protection.