In a ray diagram, a concave lens is drawn as a vertical line with inward facing arrows to indicate the shape of the lens.

Galileo played with this formula until, by the late fall of ... and blurriness caused by the curvature of the "objective" lens—the convex lens at the far end of the telescope—Galileo ground ...

Convex and concave lenses can both be used to correct defects of vision. The most commonly occurring defects of vision are ‘short sightedness’ and ‘long sightedness’. People who are ...