Question: what is the difference between double convex and biconvex lens?
Answer: A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave). ... A lens with one convex and one concave side is convex-concave or meniscus.