What is a Prime Lens?

Prime lenses as an alternative to zooms

There is a renaissance brewing among prime lenses as an alternative to zooms. The prime terminology has come into use as the reverse of zoom; meaning that a prime lens remains an optics system with a fixed-focal-distance, while an optical zoom lens encompasses a varying focal distance. Digital shooters are rediscovering prime lenses for the following reasons:

85mm Canon prime lens
Compact 85mm Canon prime lens with a maximum aperture of f/1.8

Nikon 35mm prime lens
This Nikon 35mm wide-angle lens is a small, light-weight and "fast" prime lens with a maximum aperture of f/1.8

A prime lens featuring a certain focal length is often of lighter weight, superior optical quality, lower cost, and smaller bulk, although less adaptable than a zoom lens whose span includes that same focal length, This is due to prime lens designs being less complex with less movable parts, and is specifically created for one specific focal length, while zoom lenses must operate at a wide variation of focal lengths. In addition as they encompass a less complex optical formula, these lenses do not suffer issues associated with chromatic aberration to the extent a zoom lens does (lenses ranging from 7x and higher are very likely to have this observable fact). Prime lenses generally feature a smaller f-number (larger maximum aperture) than zoom lenses do. This permits photography in lower luminance (using the same speed for the shutter) as well as realizing a more shallow depth of field.

Using 5 mm photography terminology, a "normal" prime lens customarily represents that it is prime with 50mm focal length, although that is a bit longer than the diagonal film format of 43.3 mm, that customarily defines a normal focal length. APS-C, small sensor DSLR cameras will necessitate smaller focal lengths (by their crop factor ratio) to achieve a similar angle of view.

Traditional meaning as primary lens

The traditional term for a a prime lens refers to one with an unchanging focal length and having a field of view that cannot be transformed unless a supplemental lens or teleconverter is added. In general, prime lenses are weigh less, are less expensive, sharper, and have higher quality optics than zoom lenses, Also prime lenses are easier to build than a zoom lens. By practice, traditional 35mm prime lenses have 28mm, 50mm, 85mm, 100mm and 135mm focal distances. Alternative labels of primary, fixed focal length and FFL are often employed to avoid uncertainty.

In an alternative and seemingly somewhat older connotation of the expression prime lens is that the core lens in a part of a camera/combination system. Once the lens is employed with some type of other optical device, like a teleconverter or close-up lens, the lens itself is appropriately labeled the prime lens. The word prime is used here in the implication of chief, crucial, original, principal, etc.

Lens makers such as ISCO Precision Optics, ARRI Media, Carl Zeiss AG, Schneider, Canon and other lens makers still manufacture variable focal length video and cine lenses and are repeatedly recorded as variable primes. The variable prime is often different than "true zoom" as the latter's focal length becomes varied, it stays focus This utilization of the label "prime lens" is a case in point of a retronym. In the early days of photography development only primary lenses existed (came with the camera), and were simply identified as "lenses" or "objectives". At a later time, "auxiliary" lenses became available, which were usually mounted on the front side of the front part of the principal, or "prime" lens. Updated Review Jan 28, 2011

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