Focal Length and Angle of view

Focal Length and Angle of view

The focal length of the lens is the distance between the lens and the image sensor when the subject is in focus, usually stated in millimeters (e.g., 28 mm, 50 mm, or 100 mm). In the case of zoom lenses, both the minimum and maximum focal lengths are stated, for example 18–55 mm.

The angle of view is the visible extent of the scene captured by the image sensor, stated as an angle. Wide angle of views capture greater areas, small angles smaller areas. Changing the focal length changes the angle of view. The shorter the focal length (e.g. 18 mm), the wider the angle of view and the greater the area captured. The longer the focal length (e.g. 55 mm), the smaller the angle and the larger the subject appears to be.

An AF-S DX NIKKOR 18–55 mm f/3.5–5.6G VR lens

Lens with a short focal length (wide angle of view)

The illustration is an artist’s conception.

Lens with a long focal length (small angle of view)

The illustration is an artist’s conception.

Lenses with a wide angle of view are referred to as wide-angle lenses, lenses with a small angle of view as telephoto lenses.

A zoom lens with a focal length of 18–55 mm offers the widest angle of view at 18 mm and the smallest angle of view at 55 mm. If the only lens available is an 18–55 mm zoom lens but you want wider angles—say, for landscape shots—you should buy a lens that offers focal lengths shorter than 18 mm, for example, a 10–24 mm lens. If, on the other hand, you want to photograph at greater distances, you should choose a lens that offers focal lengths longer than 55 mm, for example 55–200 mm.

Angle of view

Focal length: 12 mm	Focal length: 24 mm	Focal length: 50 mm
Focal length: 70 mm	Focal length: 135 mm	Focal length: 200 mm

The shorter the focal length, the greater the extent of the scene captured by the lens. On the other hand, the longer the focal length, the smaller the extent captured by the lens. If the same subject is photographed from the same distance, its apparent size will decrease as the focal length gets shorter and increase as the focal length gets longer.