Many articles and books on observing refer to small, medium, and large telescopes, but what are the borderlines in objective size that define small, medium, and large?

I can’t speak for every reference to small, medium, or large telescopes, but here at Astronomy, when we refer to a “small” scope we specifically mean a telescope with an aperture less than 4 inches. The type of scope doesn’t matter, and neither does the quality. Many small telescopes manufactured today are high-quality instruments that I am proud to use.

“Medium” size telescopes have apertures from 4 to 10 inches in diameter. This category contains the most popular telescopes used by amateur astronomers, a large percentage of which are 8-inch Schmidt-Cassegrain telescopes.

Finally, any telescope that uses a lens or mirror larger than 10 inches across we designate as “large.” More large telescopes are in use today than ever before, due in large part to the “Dobsonian revolution.” Newtonian reflectors coupled to relatively simple altitude-azimuth Dobsonian mounts dramatically reduced the price and weight of large telescopes from what they would have cost had they been attached to a motor-driven, equatorial mount. — MICHAEL E. BAKICH, ASSOCIATE EDITOR