Evidence suggests ancient civilizations, including the Greeks, may have had early optical knowledge and devices like ...

Instead of a concave lens near the eye ... This was the first working reflecting telescope. Other designers proved unable to grind mirrors with a regular curvature, so the reflector remained ...

As [Huygens Optics] explains, mirrors ground to each of these shapes have different properties, which makes it hard to build telescopes that work at astronomical and terrestrial distances.