Davies-Cotton telescope

A Davies-Cotton telescope is a type of visible light telescope which can be made with a sizeable collecting area at low cost, if angular resolution requirements are very low. It is used in imaging atmospheric Cherenkov telescopes (IACTs), Cherenkov detectors consisting of arrays of telescopes that are not designed to individually produce fine-grained images, but to detect incoming gamma-ray photons through the Cherenkov radiation produced by the resulting air showers. They sense the rough direction of the Cherenkov light source. Then, triangulation and timing of observation-data from a number of such individual telescopes is used to determine the trajectory of the particle that produced the Cherenkov light.

The telescope's basic concept is prime focus using a segmented primary mirror of relatively-easy-to-produce segments. As I understand the design, spherical segments of various radii are used, those of each radius arranged in a ring around the axis so together they approximate a large paraboloid mirror. It is much easier to construct a number of small spherical mirrors than a large parabolic mirror. With the design, a telescope with a primary mirror more then 10 meters across can be built at a relatively low cost, due to elimination of the ultra-precise grinding of a monolithic mirror or of sizeable non-spherical segments. The telescope-type name credits the design to a 1950s concept for a solar furnace, a device for concentrating sunlight in order to heat something. I would not be surprised if the general notion has been independently re-invented.