Definitions for "Cassegrain"
Dual-refiector antenna geometry using a convex hyperboloidal subreflector and paraboloid main reflector.
Telescope using two mirrors, in which image is passed back through the primary. Bears a superficial resemblance to the Schmidt-Cassegrain, but without the correcting lens. Usually expensive, and relatively rare. Sometimes referred to as a Classical Cassegrain.
Some telescopes, particularly at microwave and shorter wavelengths, have a second reflector near the focus of the larger, primary mirror. This translates the focal point to a position near the apex of the primary where it is more accessible, and where practical antenna feeds are less responsive to radiations arriving from very wide angles relative to the nominal pointing direction.
Cassegrain is a lunar impact crater that is located on the far side of the Moon, beyond the southeastern limb. It lies to the southeast of the larger Lebedev crater, and to the northeast of the comparably-sized Priestley crater.