Question

Write three distant advantages of reflecting type over refraction

Answer 1

1. A pure reflecting telescope does not suffer from chromatic aberration. A lens, on the other hand, bends different colors of light at different angles. (You can compensate for this with more lenses and optic coatings, but that drives the price up and decreases the light transmission.)

2. Light bent by a reflector interacts with a single surface (the mirror). Light passing through a lens interacts with two surfaces (going in and coming out); each interaction attenuates the light slightly.

3. Very large lenses are very heavy. In contrast, there are various techniques for making very thin mirrors or even segmented mirrors, which allow for larger reflectors at much lower weight (and cost). This is why all sufficiently large optical telescopes are reflectors.