The Spectrographic Equipment of the 200-INCH Hale Telescope.

The relationships between spectrograph speed and the various parameters entering into spectrograph design are discussed, and a description is given of the optical designs that have been worked out for the spectrographs of the Hale telescope to take advantage of these relationships. Three new optical features were introduced in the design of the coud6 spectrograph: (1) As dispersing element, a composite of four matched gratings is used; (2) cameras are of the Schmidt type, with the corrector plate placed practically in contact with the grating, the light passing through the plate twice, once before and once after reflection at the grating (this eliminates many of the vignetting problems present when the corrector plate is placed in the conventional position); (3) for the shortest focal-length camera an aplanatic sphere is combined with a Schmidt camera, thereby permitting a considerably higher camera speed than that attainable with the Schmidt camera alone. With the aid of these new features, a spectrograph has been constructed having a 12-inch aperture collimator beam and a series of five cameras with focal lengths ranging from 144 to 8.4 inches and yielding dispersions of 2.3 to 40 A/mm. For the study of the faintest objects a small spectrograph has been built for use at the prime focus. This has a 3-inch aperture collimator and cameras of focal length 1.4 and 2.8 inches.