convex lens

A convex lens is a lens that's thicker in the middle than at its edges.

• Held close to an object, a convex lens shows it erect and enlarged; move the object farther away, and the image flips to inverted, first still enlarged and then gradually shrinking — behaviour that closely mirrors a concave mirror's.
• A convex lens converges parallel beams of light passing through it to a point, which earns it the alternate name "converging lens."
• Because it converges light, a convex lens can concentrate sunlight into a small enough area to burn paper, exactly like a concave mirror does with reflected light.
• The lens inside the human eye is a convex lens — and a remarkable one, since it can actually change its own shape to bring both nearby books and distant scenery into sharp focus.