Question

what are the devices used in the convex as well as the concave lens

Answer 1

There are two main types of lenses: convex and concave. Convex lenses often get all the credit. They are the type of lens responsible for magnification and are the most common lens used in photography and other common applications. Concave lenses, though, serve an important role as well. A concave lens is any lens that has an inward curve in the middle. In other words, the edges of the lens are thicker than the middle. This causes light that enters the lens to spread out, or diverge. In effect, this makes images appear smaller when viewed through a concave lens.

Answer 2

A lens with one convex and one concave side is convex-concave or meniscus. It is this type of lens that is most commonly used in corrective lenses. If the lens is biconvex or plano-convex, a collimated beam of light passing through the lens converges to a spot (a focus) behind the lens.