Curved outward on both sides; describing a lens or surface that bulges outward on each of its two faces.
From 'bi-' (two) + 'convex' (curved outward), from Latin 'convexus' meaning 'vaulted.' The term became standard in optics during the 17th century when lens-making became scientifically studied.
Magnifying glasses and camera lenses are usually biconvex because the double curve focuses light rays together more powerfully than a single curve—it's the shape that helped Galileo see Jupiter's moons and changed astronomy forever.
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