The Leica R bayonet mount is a camera lens mount system introduced by Leitz in 1964. The R mount is the standard method of connecting a lens to the Leica R series of 35 mm single-lens reflex cameras.
History The mount is descended from those used for the Leicaflex (1964), Leicaflex SL (1968), and Leicaflex SL2 (1974) SLR cameras, but differs in the cams used to communicate lens aperture information to the camera. 3 cam lenses are compatible with all of the Leica SLR cameras, while R-only lenses have a slightly different mount shape that will not fit on the earlier cameras. On 5 March 2009, Leica announced plans to cease production of its R-Series manual focus SLR and lenses.
Technical
The flange focal distance between mount and film is 47 mm. Looking at the camera body from the front, the bayonet locking pin is at the 8 o'clock position alongside the stepped plunger button. At the rear of the lens, the corresponding locking slot is at the 4 o'clock position. The automatic diaphragm lever is next to the locking slot, Cam 1 is at the 12 o'clock position, and Cams 2 and 3 are at the 6 o'clock position.
R Mount camera bodies
Leicaflex
Leica R
R mount lenses R-mount lenses feature up to three mechanical cams which engage levers in the camera body. The earliest style of lens, also known as 1-cam or single cam, uses a single sloped cam which communicates the aperture setting to the camera, which is used by the original Leicaflex. Single cam lenses were discontinued in 1968 when the SL (and later SL2) were released; a second sloped cam was added to the lenses which communicated the aperture setting to the through-the-lens meter, while the first cam served to display the aperture setting in the viewfinder. 2-cam lenses were made until 1976. With the introduction of the R series cameras (R3, R4, etc.), a third stepped cam was introduced just inboard of the second sloped cam; usually, the lens had all three cams, but the R series cameras used only the third cam. 3-cam lenses were made until 1988, with the introduction of R-only lenses, and ROM contacts were introduced in 1996, which replaced cam 1 with a series of electrical contacts.
Use with other cameras The flange focal distance of 47 mm is fairly large, meaning that few other systems' lenses can be adapted to fit on a Leica R and retain infinity focus, but R lenses can be converted to other systems. The distance is only 0.5 mm larger than the Nikon F-mount, which is not sufficient to make a workable adapter, however, at least one Nikon camera has been modified with a Leica R bayonet mount to take R lenses, and at least two manufacturers make replacement mounts, allowing many Leica R lenses to be used directly on various camera systems, such as Nikon F mount cameras. For this purpose, the cams need to be removed, which is not always possible (e.g. early Elmarit-R f/2.8 35mm). The mounting flange may then need to be machined to allow free movement of the remaining cam. Sometimes, it is wise to refit the inner black anti-reflection ring, to avoid reflections within the focus mechanism (e.g. Elmarit-R f/2.8 90mm or Elmarit-R f/2.8 135mm). A further point of consideration is whether the protrusion on the rear lens block will engage with the mirror of the target SLR. For some Nikon cameras, this may be an issue. Chips can also be attached to provide focal length and maximum aperture recognition in the camera body, which provides Exif in digital cameras. A number of manufacturers have produced adapters to allow Canon EOS cameras to take R lenses, these operate only in stop-down metering mode but function well when rapid operation is not required.
See also
Leicaflex Leica R3 Leica R4-R7 Leica R8-R9 Leica M-mount Leica Camera Single-lens reflex camera
References
External links Leica R Lenses: Understanding Cams The Leicaflex: a review
