Focal Length

Focal length is the primary specification of any camera lens, measured in millimetres. It describes the distance from the lens's optical centre to the focal plane when the lens is focused at infinity. A longer focal length narrows the angle of view and magnifies distant subjects. A shorter focal length widens the angle of view and captures more of a scene in a single frame. On Micro Four Thirds, the 2x crop factor means any focal length provides a narrower field of view than on a full-frame camera, so the full-frame equivalent is calculated by multiplying the M43 focal length by 2.

Focal length is associated with specific photographic uses. Wide-angle lenses at 7-14mm native on M43 (14-28mm full-frame equivalent) are used for landscapes, architecture, interiors, and environmental subjects. Standard focal lengths around 25mm native (50mm equivalent) approximate natural human perspective. Short telephoto around 45-85mm native (90-170mm equivalent) is used for portraits. Long telephoto from 100mm native and beyond (200mm equivalent and longer) is used for wildlife, sports, and distant subjects.

Prime lenses have a fixed focal length. Zoom lenses cover a range, such as 12-100mm. Zoom lenses offer compositional flexibility at the cost of maximum aperture width, optical quality at the extremes of the range, and physical size. Prime lenses at a single focal length typically achieve higher optical performance at wide apertures and in a more compact form than a zoom covering the same focal length.

Focal length affects the apparent depth compression of a scene. Telephoto lenses make objects at different distances appear closer together than they are in reality, a perspective effect that is useful in portrait photography for flattering subject compression. Wide-angle lenses exaggerate depth, making nearby objects appear large relative to distant ones. This is why portrait photographers use moderate telephoto focal lengths rather than wide-angle lenses, where shooting close enough for a headshot with a wide angle distorts facial proportions.