Cassegrain (c. 1650-1700)

French inventor of the system of mirrors used within many modern reflecting telescopes and sometimes used in large refraction telescopes.

Nothing is known for certain about Cassegrain's life - not even his first name. Believed to have been a professor at the College of Chartres, he is variously credited with having been an astronomer, a physician, and a sculptor at the court of Louis XIV.

Cassegrain's telescope, an improvement on a design by English scientist Isaac Newton, used an auxiliary convex mirror to reflect the image through a hole in the objective - that is, through the end of the telescope itself. One intention behind this innovation was further to increase the angular magnification. A century later it was noted that this also partly cancelled out the spherical aberration (see aberration, optical).

Cassegrain also submitted a scientific paper concerning the megaphone to the Academy of Sciences in Paris.