Shape:
Convex lenses are typically shaped like a double-convex lens, where the middle is thicker than the edges. In contrast, concave lenses are typically shaped like a double-concave lens, where the middle is thinner than the edges.
Effect on Light:
Convex lenses converge parallel light rays to a focal point, making them called converging lenses. Concave lenses diverge parallel light rays, making them called diverging lenses.
Image Formation:
Convex lenses can form both real (inverted and smaller or larger than the object) and virtual (erect and magnified) images, depending on the object’s position relative to the lens. Concave lenses always form virtual, upright, and smaller images.