A letter signed L. Cassegrain described a concave primary and a convex secondary that sends the beam back through a hole in the primary. The tube is short for its focal length. Newton published a sharp reply about spherical aberration; the name still stuck.
Who Cassegrain was is still a bit thin. The layout is not: Hubble’s main optics are a Cassegrain cousin. This bench stops the return beam on a meter just ahead of the primary.