Lens mounts sizes and registers

You may find yourself  wanting to use a lens belonging to a particular photographic system on a camera made by another manufacturer and then not compatible (in the digital world it happens quite often, especially with mirrorless cameras); this is the typycal situation in which help comes from the adapter rings, which are today quite popular and promise interchangeability between systems, almost complete at least among the major ones.

The adapter ring has two main functions: the first is the physical connection, means securing connection between mounts (lens and camera body) which differ between them in diameter and often in electrical / mechanical contacts. Often the automatics present on a system cannot be replicated on the other and are lost, while still allowing you to work in manual mode. The second function is to adapt the lens register distance to make them compatible. Lens register distance or registration means in photography the distance between the focal plane of the film (or sensor) and the plane of the lens mount on the camera body and is typical of any system (SLR and otherwise) in trade now or in the past. Here lies a major problem: as the register is characteristics of each lens mount, this will be designed to focus on that particular floor and no one else thus making it impossible to use on bodies with different registration distance. The adapter rings to make up for this in two ways: if the register of the body is lower than the lens one, the difference will be offset by the sheer size of the adapter while in the opposite case, there are additional lenses that will correct the focus mistake due to insifficient registration distance, at the expense of quality which rapidly decays.

The table below summarizes the dimensional characteristics of the main mounts&bayonets systems for 16mm, 35mm, medium format and movie formats: all of them, in some way, can be used in both mirrorless and in modern digital SLR but, it is not unusual to find even adapters rings for film cameras even for less known mounts.  

MANUFACTURER MOUNT DIAMETER (mm) REGISTER (mm)
Aaton A bayonet 50 40
Alpa Alpa bayonet 42 37,8
Altix BL 34 42,50
Argus C bayonet 33 44,45
Arri Arriflex 41 52
Arri PL 54 52
Arri Maxi PL 62 52
Bolex standard 25,40 23,22
Bolex H8RX 25 15,31
Bronica S 57 101,70
Bronica ETR 69
Bronica GS
Canon EF 54 44
Canon FL/FD 48 42,10
Contarex standard 46
Contax RF dual  34,85
Contax C/Y (Yashica) 45,50
Contax G 29
Contax N 48
Eclair standard 48
Exacta Topcon standard 44,70
Exacta 66 74,10
Fujica X 43,50
Hasselblad standard 82,10
Hasselblad V 74,90
Hasselblad XP 34,30
Icarex 35 standard 48
Kiev 60 74,10
Kiev MST 88 82,10
Kodak Retina 44,70
Konica AR 40,70
Konica F 40
Konica HRF 39 28,80
Kowa Six 79
Leica M 27,95
Leica R 47
Leica V 39 28,80
Mamiya 7 59,95
Mamiya 645 63,30
Mamiya RB 112
Mamiya RZ 105
Mamiya ZE 45,50
Minolta AF 44,60
Minolta SR 41 43,70
Miranda standard 44 41,50
Mitchell BNCR 68 61,47
Nikon F 44 46,50
Nikon S 49 34,85
Panavision PVM 49,50 57,15
Pentacon Six 74,10
Pentax 67 84,95
Pentax 645 70,87
Pentax A110 27
Pentax K 45,46
Vari C Mount 25,40 17,53
Vari D Mount 15,88 12,29
Vari M39 39 28,80
Vari M42 42 45,50
Vari T/T2 42 55
Zenit MST 74,10

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