The Complete Handbook of Camera Lenses

Chapter 1: Understanding Camera Lenses

The Lens as an Optical System

A camera lens is, at its core, a precisely shaped piece of glass (or sometimes plastic or crystal) that projects an image onto a light-sensitive surface. It takes the chaotic, multi-directional light reflecting off a scene and bends it into an orderly, focused two-dimensional representation of that scene. This simple physical action is the foundation of all photography and cinematography. The camera body, with its sensor or film, is merely a light-tight box that records the projected image. The lens is the brain that determines the perspective, the depth of field, the luminosity, and ultimately the character of that recorded image.

Understanding how a lens forms an image is fundamental to using it effectively. The oldest and most basic lens design is the single convex element, like a magnifying glass. When light rays from a distant object pass through a convex lens, they are refracted, or bent, and converge at a point behind the lens. This point, where the rays from an infinitely distant source meet, is called the focal point. The distance from the optical center of a lens to its focal point is the focal length, measured in millimeters. This single parameter, focal length, is the single most important descriptor of a lens's field of view and magnification. A 50mm lens has a specific angle of view; a 200mm lens has a narrower angle of view, magnifying the subject; a 16mm lens has a wider angle of