# Lens bayonet

Lens bayonet of a camera system with manual focusing (Minolta MC / MD)
A lens with mechanical transmission elements for aperture control (Nikon AI-S)
Camera side:
above: cam for bayonet locking,
below: lever for controlling the lens aperture (Minolta MC)
A bayonet with electrical contacts for lens data and mechanical transmission elements for autofocus and aperture (Pentax KAF)
Bayonet adapter FTZ on the camera side

A lens bayonet is the most common lens connection for interchangeable lenses in photo technology . It is designed differently depending on the manufacturer and is based on "noses" around the rear lens of the objective, which engage in corresponding recesses in the flange ring on the camera housing.

The advantage of a bayonet connection compared to screw connections is that it is easy to use: The attachment position is usually marked with a colored point on the camera housing and lens. With a turn (usually by 60 to 90 degrees), the lens and camera are coupled with one another and you don't have to change your grip. It only requires precise positioning and turning to lock it into place; when the correct coupling is achieved, the lens engages. The lens can be unlocked again using a button on the camera housing or lens.

The distance between the film or sensor and the lens support on the bayonet is known as the flange focal length , it differs depending on the manufacturer and is often around 45 mm for 35 mm reflex cameras, and usually less than 20 mm for mirrorless systems of the same image format .

In addition to the pure fastening function, elements of the sensors and actuators are usually integrated in the bayonet:

• The camera housing is informed (by means of a lug or electrical contacts) by how much the incidence of light will be reduced during the exposure process when the open aperture of the lens closes to the preselected value for exposure.
• Shortly before the exposure process, the housing instructs the lens to close the aperture: usually by relieving a pretensioned spring of the lens by a certain distance.
• With autofocus cameras, the lens groups in the lens are shifted in order to focus using a motor. Depending on the model and manufacturer, this motor can be located in the camera housing and is coupled to the lens via a shaft in the lens bayonet, or the entire drive is located in the lens, and only an electrical transmission of control information takes place.
• Modern bayonets for digital cameras transmit a great deal of additional information between the camera electronics and lens, such as the set focal length or information relating to anti-shake mechanisms. Some of them are saved in the Exif data.

## Current bayonets in digital photography

The maximum aperture angle on the image side results from the diameter of the exit pupil and the flange focus as follows: ${\ displaystyle \ omega _ {max}}$${\ displaystyle A}$${\ displaystyle a}$

${\ displaystyle \ omega _ {max} = 2 \ arctan {\ frac {A} {2a}}}$

The Abbe sine condition can be used to determine the minimum f-number at which theoretically no image errors must occur on the image axis: ${\ displaystyle k_ {min}}$

${\ displaystyle k_ {min} = {\ frac {1} {2 \ sin {\ frac {\ omega _ {max}} {2}}}}}$
bayonet Sensor size Back focus ${\ displaystyle a}$ diameter ${\ displaystyle A}$ Maximum opening angle on the image side
${\ displaystyle \ omega _ {max}}$
Minimum f-number ${\ displaystyle k_ {min}}$ Camera type Camera series
Canon EF Full format 44 mm 54 mm 63 ° 0.96 (D) SLR Canon EOS
Canon EF-M APS-C 18 mm 47 mm 105 ° 0.63 DSLM Canon EOS M
Canon EF-S APS-C 44 mm 54 mm 63 ° 0.96 DSLR Canon EOS
Canon RF Full format 20 mm 54 mm 107 ° 0.62 DSLM Canon EOS R
Fujifilm G. Medium format 26.7 mm 65 mm 101 ° 0.65 DSLM Fujifilm GX
Fujifilm X APS-C 17.7 mm 44 mm 102 ° 0.64 DSLM Fujifilm X
Leica L Full format and APS-C 20 mm 51.6 mm 104 ° 0.63 DSLM Leica CL, SL , TL2; Panasonic Lumix S; Sigma
Leica M Full format 27.8 mm 44 mm 77 ° 0.81 Rangefinder / DSLM Leica M
Leica S Medium format 53 mm 66 mm 64 ° 0.95 DSLR Leica S
Micro Four Thirds 4/3 ″ 19.25 mm 38 mm 89 ° 0.71 DSLM Olympus Pen, OM-D; Panasonic Lumix G
Nikon 1 1" 17 mm 40 mm 99 ° 0.66 DSLM Nikon 1
Nikon F Full format and APS-C 46.5 mm 44 mm 51 ° 1.17 (D) SLR
Nikon Z Full format and APS-C 16 mm 55 mm 120 ° 0.58 DSLM Nikon Z 6 , Z 7 , Z 50
Pentax K Full format and APS-C 45.46 mm 44 mm 52 ° 1.15 (D) SLR
Pentax Q 1 / 2.3 ″, 1 / 1.7 ″  9.2 mm 31 mm 119 ° 0.58 DSLM
Pentax 645 Medium format 70.87 mm 61.2 mm 47 ° 1.26 (D) SLR
Sigma SA Full format 44 mm       (D) SLR / DSLM
Sony A Full format and APS-C 44.5 mm 49.7 mm 58 ° 1.03 (D) SLR Sony α
Sony E Full format and APS-C 18 mm 46.1 mm 104 ° 0.63 DSLM Sony α (also known as NEX)

SLR = analog single-lens reflex camera, DSLR = digital single-lens reflex camera, DSLM = mirrorless system camera

## Historical and classic bayonet connections

Well-known historical and classic bayonet connections for 35mm cameras are u. a.

A well-known bayonet connection for medium format cameras is the P6 bayonet originally developed for the Praktisix , but widely used by the Pentacon Six and the Kiev 60 .