You can take any lens shape and picture light going through it. Using the laws of refraction that you learned (FST and SFA), you can demonstrate the way the light will bend when it goes into the lens and out of it.

In the diagram below, you see some common lens shapes. The one on the left is known as a double convex lens, because both sides curve outward. The one on the right is a double concave lens.

CONVEX LENSES

Convex lenses are the most common type of lens. Look at the convex lens on the left of the diagram. When the light enters the lens, it bends. Since it’s going from a faster to a slower medium, it bends toward the normal line. Upon exiting the lens, it bends again, away from the normal line (remember, the normal line is the line drawn perpendicular to any point on the curve). Both bends cause the light ray to converge.

The illustration below is a wavefront after passing through a convex lens.