What does "focal length" refer to in optical calculations?

Focal length is defined as the distance from a lens to the point where light rays that are parallel to the optical axis converge after passing through the lens. This point is known as the focal point. The significance of the focal length lies in its role in determining the lens's power; shorter focal lengths indicate more powerful lenses that bend light more sharply, while longer focal lengths correspond to weaker lenses.

In optical calculations, understanding focal length is crucial as it directly influences the magnification and imaging properties of lenses. For instance, in photography, the focal length dictates how much of a scene can be captured and the level of detail rendered in images.