Zooms

Zooms refer to the ability to change the focal length of a camera lens, thereby altering the magnification and field of view without moving the camera. In common usage, “zoom” describes either optical zoom produced by a zoom lens or digital zoom created by image processing. Optical zoom preserves image resolution because it re-frames the scene with lens elements, while digital zoom crops and enlarges the image, which reduces sharpness and detail.

A zoom lens contains groups of glass elements that extend or contract relative to one another as the user turns the zoom ring or activates a motor. The zoom ratio is the ratio of the longest focal length to the shortest. Lenses are categorized by their focal-length range, such as standard zooms (roughly 24–70 mm), wide-angle zooms (16–35 mm), and telephoto zooms (70–200 mm). Some designs offer a constant maximum aperture across the range; others vary, becoming slower at longer focal lengths.

Focus behavior varies: parfocal zooms tend to maintain focus during zooming, while many everyday zooms are not perfectly parfocal and require refocusing when zooming. Image stabilization and coatings affect performance across the range. In video work, zooms are often motorized to provide smooth, controlled changes in focal length with minimal operator input.

Applications include photography of landscapes, events, wildlife, and cinema; zooms enable versatile framing and a single lens to cover multiple focal lengths. Limitations include potential drops in sharpness, color, and contrast toward the extremes of the range, increased size and weight, and higher cost relative to prime lenses. Digital zoom should be avoided for quality unless cropping is impractical.