What is Principal Focus?

Answer: The principal focus is generally related to physics, and to be more precise, and it is related to the lens. The principal focus of a lens is generally defined as the point at which the rays passing parallel to the principle converge in the case of a convex lens and appear to diverge virtually in the case of a concave lens. After refraction through the lens, the light rays moving parallel to the principal axis pass through this point which is called the principal axis.

Convex lens: In the case of a convex lens, the rays passing parallel to the principal axis converge to a given point. That given point is termed as the principal focus of a convex lens.

Concave lens: In the case of a concave lens, the light rays which diverge from the point appear to meet at the point virtually, which is known as the principal focus of a concave lens.

This point is usually helpful in drawing the optics diagram and the ray diagrams. This principle focus point is a very important point as all the light rays converge to this point or diverge from this point, and this point is essential for drawing the ray diagrams of physics.