Final answer:
Reflecting telescopes are the type of telescopes with a concave mirror in the aperture. They use a concave mirror to focus light, allowing the construction of larger and more cost-effective telescopes compared to those using lenses.
Step-by-step explanation:
Telescopes that utilize a concave mirror in their aperture are known as reflecting telescopes. A concave mirror, with a shape similar to the inner surface of a sphere, reflects and focuses incoming light to a single point. This primary mirror is usually coated with a reflective metal like silver, aluminum, or sometimes gold, to maximize its reflectivity. The concave mirror, therefore, is able to produce images just as a lens can. In particular, a common design that uses this principle is the Cassegrain telescope which incorporates a convex secondary mirror and a primary concave mirror with a hole, allowing light to be directed to an eyepiece or a detector.
Reflecting telescopes, using mirrors, offer advantages over refractors, which use lenses. Mirrors only require polishing on one surface and can be made much larger than lenses, allowing them to capture more light and thus be more suitable for viewing distant astronomical objects. This makes reflectors more cost-effective, especially for larger apertures.