Lens mount

A lens mount is an interface — mechanical and often also electrical — between a photographic camera body and a lens. It is confined to cameras where the body allows interchangeable lenses, most usually the single lens reflex type or any movie camera of 16 mm or higher gauge. Lens mounts are also used to connect optical components in instrumentation that may not involve a camera, such as the modular components used in optical laboratory prototyping which join via C-mount or T-mount elements.

A lens mount may be a screw-threaded type, a bayonet-type, or a friction lock type. Modern still camera lens mounts are of the bayonet type, because the bayonet mechanism precisely aligns mechanical and electrical features between lens and body. Screw-threaded mounts are fragile and do not align the lens in a reliable rotational position, yet types such as the C-mount interface are still widely in use for other applications like video cameras and optical instrumentation.

Bayonet mounts generally have a number of tabs (often three) around the base of the lens, which fit into appropriately sized recesses in the lens mounting plate on the front of the camera. The tabs are often "keyed" in some way to ensure that the lens is only inserted in one orientation, often by making one tab a different size. Once inserted the lens is fastened by turning it a small amount. It is then locked in place by a spring-loaded pin, which can be operated to remove the lens.

Lens mounts of competing manufacturers (Nikon, Canon, Contax/Yashika, Pentax, etc.) are almost always incompatible. Many allege that this is due to the desire of manufacturers to "lock in" consumers to their brand. However, since there are other differences between manufacturers — specifically the flange focal distance from the lens mount to the film or sensor — one would not want to mount a lens which wasn't specifically designed for their type of camera, at least not without an adapter to correct the spacing.

In movie cameras, the two most popular mounts in current usage on professional 35 mm cameras are Arri's PL mount and Panavision's PV mount. The Panavision mounts are exclusively used with Panavision lenses, and thus are only available on Panaflex cameras or third-party cameras "Panavised" by a Panavision rental house, whereas the PL mount style is favored with most other cameras and cine lens manufacturers. Both of these mounts are held in place with locating pins and friction locking rings. Other mounts which are now largely historical or a minority in relation to current practices are listed below.

List of lens mount types

These types are organized by category; find details in the section that follows.

;Stills
* Canon EF
* Canon EF-S
* Canon FD
* Canon FL
* Contax N
* Contax/Yashica bayonet
* Four Thirds System
* Fujica X bayonet
* Konica original bayonet
* Konica AR 47mm bayonet
* Leica M mount
* Leica R bayonet
* M42
* Mamiya bayonet
* Micro Four Thirds System
* Minolta AF
* Minolta MD
* Miranda bayonet (all Miranda cameras had a dual bayonet/M42 screw mount)
* Nikon F
* Olympus OM
* Pentax K
* Sigma SA
* T-mount (T-thread)
* Yashica AF

;Cine
* Aaton universal
* Arri bayonet
* Arri PL
* Arri standard
* B4
* BNCR
* C mount
* CA-1
* PV (Panavision)

;Industrial
* C mount
* CS mount
* Front-plate mount

List of lens mounts

This list of lens mounts is ordered by flange focal distance, from shortest to longest. It includes both digital, still photography and movie lens mounts.

Legend

econdary lens mount

Secondary lens refers to a multi-element lens mounted either in front of a camera's primary lens, or in between the camera body and the primary lens.

(D)SLR camera & interchangeable-lens manufacturers offer lens accessories like extension tubes and secondary lenses like teleconverters; which mount in between the camera body and the primary lens, both using and providing a primary lens mount.

Canon PowerShot A and Canon PowerShot G cameras have a built-in or non-interchangeable primary (zoom) lens; and Canon has "conversion tube" accessories available for some Canon PowerShot camera models which provides either a 52mm or 58mm "accessory/filter" screw thread. Canon's close-up, wide- (WC-DC), and tele-conversion (TC-DC) lenses have 2, 3, and 4-element lenses respectively, so they are multi-element lenses and not diopter "filters".

Notes

4/3's published facts:
*"Size of the 4/3-type Sensor: The standard diagonal length of the sensor is Convert|21.63|mm|in. It is half that of 35-mm film format (Convert|36|mm|in x Convert|24|mm|in = Convert|43.27|mm|in) and suitable format for professional use in digital age. The image circle of the interchangeable lens is specified based on this diagonal length. The focal length is about a half that of a 135 film camera lens assuming the same angle of view." [Cite web
title=About Four Thirds, Standard, Whitepaper (Summary of Standard)
publisher=Four Thirds System
url=http://www.four-thirds.org/en/about/standard.html
format=HTML
accessdate=2008-08-11]
*"The foundation for the high picture quality of the Four Thirds system is the lens mount, which is about twice the diameter of the image circle." [Cite web
title=About Four Thirds, Standard, Benefits of Four Thirds
publisher=Four Thirds System
url=http://www.four-thirds.org/en/about/benefit.html
format=HTML
accessdate=2008-08-11]
*"Differences between Four Thirds System mount and Micro Four Thirds System mount: Mount diameter reduction; As a result of research aimed at facilitating the design of compact, lightweight lenses while maintaining the current strength, the outer diameter of the lens mount has been reduced by approx. Convert|6|mm|in. ... the Micro Four Thirds System ... specifies the optimum flange back length required to reduce camera size and thickness, assuming the omission of the mirror box. The flange back length has been reduced to about 1/2 that of the Four Thirds System." [Cite web
title=Micro Four Thirds, Standard, Whitepaper (Summary of Standard)
publisher=Four Thirds System
url=http://www.four-thirds.org/en/microft/whitepaper.html
format=HTML
accessdate=2008-08-11]

So:
*21.63mm * 2 = Convert|43.26|mm|in or ~44mm
*43.26mm - 6mm = Convert|37.26|mm|in or ~38mm
*(21.63mm)^2 = ( ( 17.3mm ^ 2 ) + ( 12.98mm ^ 2 ) ); See: Pythagorean theorem (5^2 = 4^2 + 3^2)

NOTE:Some published reviews of 4/3 instead cite the (female) "outside diameter" of the lens or mount as ~50mm (and micro-4/3 as ~44mm),Cite web
title = Olympus and Panasonic announce Micro Four Thirds
publisher = Digital Photography Review
url = http://www.dpreview.com/news/0808/08080501microfourthirds.asp
format = HTML] , and not the appropriate "major" diameter (D) ~44mm which is the camera body's female mount inside-diameter and the lens's male mount outside-diameter (micro-4/3 ~38mm).

References

General references

*Cite web |url=http://www.a1.nl/phomepag/markerink/mounts.htm |title=Camera mounts & registers |author=Markerink, Willem-Jan

See also

*ISO metric screw thread

External links

* [http://members.tripod.com/rick_oleson/index-99.html SLR Mount Identification Guide]
* [http://www.zenitcamera.com/qa/qa-gost10332-72.html Standard: GOST 10332-72 (in Russian) — M42×1/45.5, M39×1/28.8]
* [http://www.zenitcamera.com/qa/qa-gost10332-63.html Standard: GOST 10332-63 (in Russian) — M39×1/45.2 (aka «Z39»), M39×1/28.8, bayonet «C» (cameras: «Zenit-5», «Zenit-6», «Zenit-7»), bayonet «Zenit-7»]