The largest reflecting
telescopes in the world are the pair of Keck telescopes in Hawaii, USA,
with a reflector of 10 metre in diameter Rationalised 2023-24
Ray Optics and
Optical Instruments
247
3 Cartesian sign convention: Distances measured in the same direction
as the incident light are positive; those measured in the opposite
direction are negative All distances are measured from the pole/optic
centre of the mirror/lens on the principal axis