Fixed Lenses

Lenses that have a fixed or one focal length are known as prime lenses and these comprise a small but important segment of the market because they are generally used by more seasoned camera users and professional photographers. The name prime has come to be used as the complete opposite of zoom; that is, a prime lens is a fixed focal length, or unifocal lens, whilst a zoom lens has a varying focal length.

A prime lens of a given focal length is even less convenient than a zoom whose range incorporates that focal length, but it is frequently of much better optical quality, lighter, smaller in bulk and lower price tag. In comparison with a zoom lens, a prime lens contains less moving parts and optimisation for just one specific focal length. By using a less complicated lens system they are afflicted by a lower number of issues associated with chromatic aberration.

Prime lenses usually have a larger maximum aperture (smaller f-number) than zoom lenses. This enables photography in reduced light and with a shallower depth of field.