The principal focus of a lens is the point on the principal axis where parallel rays of light, after passing through the lens, converge or appear to diverge from. For a convex lens, these rays converge to a point, while for a concave lens, they appear to diverge from a point on the principal axis.
What is the principal focus of a lens, and how is it related to the behavior of parallel rays of light?
Share
The principal focus of a lens is the point on the optical axis where parallel rays of light either converge or appear to diverge after passing through the lens. For a converging lens (convex), parallel rays converge at a real focal point, while for a diverging lens (concave), they appear to diverge from a virtual focal point. The behavior is described by the lens formula: 1/f = 1/u+ 1/v , where f is the focal length, u is the object distance, and v is the image distance. The principal focus is a key parameter in understanding lens behavior in optical systems.