Reflector

A reflector is a telescope that gathers and focuses light using a curved primary mirror at the back of the tube instead of a lens at the front. Light bounces off this mirror onto a smaller secondary mirror, which redirects it out to an eyepiece near the side or top of the tube, depending on the design. Because mirrors are cheaper to produce in large sizes than equivalent lenses, reflectors deliver more aperture for the same budget than a refractor of similar price.

The main tradeoff is maintenance. An open tube design lets air, and with it dust and moisture, reach the mirrors, and the mirrors can drift out of alignment over time, transport, or temperature changes. This means reflectors periodically need collimation, the process of realigning the mirrors, to keep images sharp, especially at higher magnifications used for planets and double stars.

Reflectors are the backbone of budget-friendly, large-aperture telescopes, particularly Dobsonian designs, making them a common first serious telescope for observers who want to see faint galaxies and nebulae. A frequent mistake is buying a reflector and never learning to collimate it, which leads to blurry, bloated star images that get blamed on the telescope's quality rather than a simple alignment issue that takes only a few minutes to fix.