Fixed focal length refers to a camera or lens system in which the focal length is set at a single, unchanging value and cannot be adjusted or substituted for a lens of a different focal length. In the context of a camera system, it describes a camera whose lens is permanently attached and cannot be removed or exchanged, limiting the photographer to the single angle of view and perspective provided by that lens. In the context of an individual lens, the term describes a prime lens - one that offers a single fixed focal length rather than a variable zoom range.
Cameras with fixed focal length lenses are most commonly found among compact and point and shoot cameras, where a single lens of a moderate wide angle focal length - typically equivalent to around 28mm to 35mm in 35mm format terms - is permanently built into the camera body. While this limits compositional flexibility compared to interchangeable lens systems, it allows the camera to be made smaller, lighter, and more affordable, and removes the need for the photographer to carry and manage multiple lenses.
Fixed focal length lenses, or prime lenses, used on interchangeable lens camera systems offer a number of optical and practical advantages over zoom lenses. Because the optical design does not need to accommodate a range of focal lengths, prime lenses can be engineered to deliver superior sharpness, contrast, and optical quality, often at wider maximum apertures than equivalent zoom lenses. This makes them particularly valued for portrait, street, low light, and reportage photography where image quality and maximum light gathering ability are priorities.
Many photographers also argue that working with a fixed focal length encourages a more considered and disciplined approach to composition, as the photographer must physically move closer to or further from the subject rather than relying on a zoom control, leading to a more intimate and engaged relationship with the scene being photographed.