Yoshiya Matsui

Fast camera for a spectrograph

The optical design and fabrication of a fast f/1.4 prototype camera for the JNLT are briefly described. The f/1 semisolid Schmidt-Cassegrain camera configuration (a corrector lens plus two aspheric mirrors) developed by Nariai and Yamashita (1987) on the basis of third-order aberration theory is adopted, but the design is modified to reduce the number of aspheric surfaces from four to two. Computer-controlled polishing achieved accuracy of 150 and 200 nm for the corrector plate and secondary mirror, respectively. The use of a constant-radial-shearing interferometer to test the Schmidt corrector plate is explained, and it is reported that the assembled camera had MTF of 55 percent for 100 lp/mm when imaging a 5-micron slit placed in the focal plane.