A New Interferometric Test and its Application to the 84-in. Reflecting Telescope at Kitt Peak National Observatory
The 84-in.-aperture Cassegrainian-type telescope at Kitt Peak National Observatory was tested with a wavefront-shearing interferometer. This test provided the optical path differences between 538 uniformly spaced rays in the annular beam of light transmitted by the telescope. Independent tests were made from photographs taken on each of two consecutive nights. The following results were obtained from this test: (a) the coordinates of the points of incidence of each of the 538 rays on the focal plane (a spot diagram); (b) a measure of primary astigmatism; and (c) the deviation of the wavefront, at 538 uniformly spaced points, from a sphere that is centered on the ideal image point. A description of the mathematical operations is given with the results. The results show a measurable change in the waveform during the test periods (approximately 30 min) each night and a larger difference from one night to the next.