The Cassegrain telescope was invented in about 1672 by Sieur Guillaume Cassegrain, a sculptor and metal founder employed by the King of France. The mirrors were probably made of speculum or some similar metal which could take a polish. Cassegrain communicated his design to Monsieur de Bercèe who took it to the French Academy and by May of that year the idea had appeared in Journal des Sçavans and Philosophical Transactions. Almost immediately a dispute erupted concerning the relative qualities of the Cassegrain and two English telescope types, the newly invented Newtonian telescope and the older Gregorian design. Battle lines among scholars and their scientific academies were drawn along national boundaries – in this case down the middle of the English Channel. Even Sir Isaac Newton himself joined the fray and published dissertations establishing his claims.

The Gregorian telescope is composed of a concave parabolic primary mirror with a concave elliptical secondary. The Cassegrain uses a similar concave parabolic primary with a convex hyperbolic secondary. The Newtonian has a concave parabolic primary with a plane secondary. All three designs had the advantage of no color aberration since they used mirrors instead of lenses. The invention of the achromatic lens was a half century in the future at the time. The Gregorian design was popular because it produced an erect image and it was free from spherical aberration – theoretically.