Definition of Cassegrain telescope
: a reflecting telescope that has a paraboloidal primary mirror and hyperboloidal secondary mirror, is equivalent in its optical effects to a telephoto lens, and usually has the light brought to a focus through a perforation in the center of the primary mirror
From the M-W Editors
Origin and Etymology of cassegrain telescope
after Laurent Cassegrain †1693 French priest and teacher credited with its invention
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