Abstract
Several modifications of the Cassegrainian-type telescopic system using a spherical secondary mirror are discussed in terms of the effect of such modifications on the image quality at moderate apertures and focal lengths. Both third-order and trigonometric methods are used to compare the various systems. It is found that an f/11 true Cassegrainian system of EFL 130 inches gives excellent image rendition over a field of approximately 1.7 degrees, while a more easily manufactured modified system of the same optical dimensions using a spherical secondary mirror and an ellipsoidal primary mirror gives equivalent image rendition over a field of approximately 0.42 degree.
Published Version
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