A rare look at NASA’s next sharp-eyed space telescope
The central feature of the telescope is an exquisitely polished, concave primary mirror, 2.4 meters (7.9 feet) in diameter.
PBS3y
Two Types of Telescopes
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 ...