How Do Lens Refract Light

How does a Lens Refract Light?
Different Lenses refract light in different ways. First, we will look at a double convex lens. Several light rays will approach the convex lens in a parallel manner. After they approach the lens, each ray will refract towards the normal. The light is passing from an optical less dense medium (Air) into a more dense medium (such as plastic or glass) at this boundary. Since the light rays are passing the boundary from a less dense medium in which light travels fast (optically less dense) into a more dense medium in which light travels slowly (more optically dense), light will refract towards the normal line. This is demonstrated by the two incident rays in the diagram above about the refraction by a converging lens. Once light refracts from the boundary and
The incident rays will, rather, diverge upon refraction within the lens. Because of this, double concave lenses cannot reveal real images, but images that are virtual (not real). But if we backtrack the refracted rays, the rays will then intercept at a point; this is the focal point. The concave lens will have a negative focal length since the rays that travelling parallel as it enters the front of the lens to the principal axis, will diverge as it exits the lens.
Now let’s assume that the light rays are travelling towards the focal point of the lens. Light rays will approach the focal point from the opposing side of the concave lens, this is due to the negative focal length of the lens. As we already know, the light rays will refract as they enter the lens and refract again as they exit the lens. Because the light is entering a more dense medium, refraction occurs towards the normal and as they approach the less dense medium, refraction occurs away from the normal. These rays will then travel parallel to the principal axis.

Refraction