Prime lens

In film and photography, a prime lens is either a photographic lens whose focal length is fixed, as opposed to a zoom lens, or it is the primary lens in a combination lens system.

Confusion can sometimes result due to the two meanings of the term if the context does not make the interpretation clear. Alternative terms "primary" and "fixed focal length" or "FFL" are sometimes used to avoid ambiguity.

As alternative to zoom

The term "prime" has come to be used as the opposite of "zoom;" that is, a prime lens is a fixed-focal-length lens, while a zoom lens has a variable focal length. [cite book | title = The Super 8 Book | author = Lenny Lipton | publisher = Simon andSchuster | year = 1975 | isbn = 0879320915 | pages = p.61 | url = http://books.google.com/books?id=uOdTAAAAMAAJ&q=zoom+prime+fixed-focal-length++date:0-1980&dq=zoom+prime+fixed-focal-length++date:0-1980&lr=&as_brr=0&ei=x-KvR93nGaeGtgPl3pmIBg&pgis=1 ] [cite book | title = Filming for Television | author = A. Arthur Englander and Paul Petzold | publisher = Hastings House | year = 1976 | url = http://books.google.com/books?id=sFgFAAAAMAAJ&q=%22zoom+or+prime%22+date:0-1980&dq=%22zoom+or+prime%22+date:0-1980&lr=&as_brr=0&ei=kuCvR-fLLIXasQO1y9WLBg&pgis=1 ] [cite book | title = Effective TV Production | author = Gerald Millerson | publisher = Focal Press | year = 1993 | isbn = 024051324X | url = http://books.google.com/books?id=mjkB1hMZZtoC&pg=PA32&dq=%22prime+lens%22+%22zoom+lens%22+fixed+focal-length&lr=&as_brr=3&ei=6duvR9zgLZGOswPUrImgAw&sig=evtOHziEGHRTBWdbOXgypNLhNMk ]

A prime lens of a given focal length is less versatile than a zoom whose range includes that focal length, but is often of superior optical quality, lighter weight, smaller bulk and lower cost. This is because prime lens designs are simpler (fewer moving parts), and can be optimized for one particular focal length, whereas zoom lenses must function at a variety of focal lengths. Also since they sport a less complicated lens formula, these lenses won't suffer problems related to chromatic aberration as much as a zoom lens (lenses sporting from 7x and above are very prone to this phenomenon)Fact|date=March 2008.

Prime lenses usually have a larger maximum aperture (smaller f-number) than zoom lenses. This allows photography in lower light (with the same shutter speed) as well as achieving a shallower depth of field.

In 35mm photography a "normal" prime commonly refers to a prime lens with 50mm focal length, though that is somewhat longer than the film format diagonal of 43.3 mm, which is typically taken to define a normal focal length. Small sensor digital cameras will require shorter focal lengths (in the ratio of their crop factor) to have the same angle of view.

Traditional meaning as primary lens

An alternate and apparently somewhat older meaning of the term "prime lens" is the main lens in a combination lens system. [cite book | title = The British Journal of Photography | publisher = Liverpool Photographic Society | year = 1967 | edition = v.115 | url = http://books.google.com/books?id=ZIAqAAAAMAAJ&q=prime-lens+date:0-1950&dq=prime-lens+date:0-1950&lr=&as_brr=0&ei=M-WvR5rJJ5aytgOZsuSDBg&pgis=1 ] When the camera lens is used with some other optical device, such as a close-up lens or tele converter, the camera lens itself is properly called the "prime lens". "Prime" is here used in the sense of primary, chief, original, first in order, etc.

Lens manufacturers such as ARRI Media, [cite web|url=http://www.arrimedia.com/productlist.php?catalog_id=193 |title=ARRI Variable Prime Lenses |accessdate=2007-11-19 |work=ARRI Media ] ISCO Precision Optics, [cite web|url=http://iscoprecisionoptics.com/Downloads_new/Product_information/ISCO_PL_VP_System_US_02_2007.pdf |title=Variable Prime System for 35 mm Film |accessdate=2007-11-19 |work=ISCO Precision Optics ] Schneider, [cite web|url=http://www.schneideroptics.com/ecommerce/CatalogSubCategoryDisplay.aspx?CID=67 |title=Variable Prime |accessdate=2007-11-19 |work=Schneider Optics ] Zeiss, [cite web|url=http://www.oscars.org/scitech/1998/winners.html |title=1998 Scientific & Technical Awards Winners |accessdate=2007-11-19 |work=Academy of Motion Picture Arts and Sciences ] Canon, [cite web|url=http://wwwdb.oscars.org/ampas/plsql/ampas_award.detail?primekey_in=1999070715:59:34802212511 |title=AMPAS Award |accessdate=2007-11-19 |work=Academy of Motion Picture Arts and Sciences ] and others still make variable focal length cine and video lenses regularly catalogued as "variable primes". A variable prime is sometimes distinguished from a "true zoom" in that the latter maintains focus as the focal length is varied.

This use of the term "prime lens" is an example of a retronym. Early in photography only primary camera lenses were available, and were merely called "lenses" or "objectives". Later, "auxiliary" lenses were available, which usually fit in front of the front element of the primary, or "prime" lens.

References

External links

* [http://photonotes.org/cgi-bin/entry.pl?id=Primelens Photo Dictionary definition]
* [http://www.the-digital-picture.com/Canon-Lenses/Zoom-Vs-Prime-Lens.aspx Zoom vs. Prime Lenses]