... A concave lens will refract light inwards, thus creating a smaller image while a convex lens will do the opposite, creating a larger image. All lenses have an optical centre, where light can pass without being refracted and the principal axis of the lens passes though this point. At this point on the lens, the glass (or other material) is flat on both sides of the lens. When light passes through the lens anywhere except the optical centre, the rays are refracted, either towards the principal axis, in the case of a convex lens, or away from it, in concave lenses. Lenses also have a focal point, which is the point at which the refracted rays converge with one another. In a convex lens this is on the opposite side of the lens to the object, but in a concave lens, where the refracted rays are directed away from the principal ...

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