A convex lens and a concave lens differ in that the convex lens makes parallel rays:

1. The two lens types are defined by opposite effects. 2. The concave lens is a diverging lens that bends rays away from its axis. 3. The converging lens takes rays entering parallel to its axis. 4. Those rays cross one another at a single point on the opposite side. 5. So the convex lens gathers where the concave lens spreads. _Source: OpenStax College Physics for AP Courses 2e (CC BY 4.0), Ch 25 'Geometric Optics', sections 25.1-25.7_