Leitz introduced LEICAFLEX, their first SLR, in 1964. It was an all-mechanical camera with external CdS cell built into the pentraprism. The LEICAFLEX SL (1968) introduced a TTL ("Selective Light") open-aperture metering (and removed the mirror lock-up feature that was available on the predecessor). The LEICAFLEX SL2 (1974) was a minor upgrade: it offered an additional split-image rangefinder for positive focusing, and a more sensitive exposure meter, as well as an additional accessory-shoe contact.
In order to offer automatic exposure, Leitz teamed up with the Japanese company Minolta. The new LEICA R series cameras were based on Minolta electronics but produced by Leitz in Germany or Portugal. The R3 ELECTRONIC (1976) was the first auto-exposure (aperture-priority) SLR by LEICA based on the XE, the R4 (1980) was a more compact XD-based model which also offered shutter-priority and programmed auto-exposure modes, while the R5 (1986) also added TTL flash exposure metering. The R-E (1990) was an economy version of the R5 with reduced set of features, the all-mechanical R6 (1988) had no auto-exposure, while the R7 (1992) was a redesign of the R5.
The R8 (1996) became a totally new in-house design with new line of accessories. The R9 (2002) was a slight modification of the R8. A 10MP digital back called DIGITAL-MODUL-R transformed these analog cameras into digital.
Leica R lenses combined high resolving power with high image contrast to provide exceptional picture sharpness. The focal lengths ranged from a 15mm wide-angle to a 800mm telephoto. Anti-reflection coatings on highly refractive glasses assured almost 100% light transmission within the entire visible spectrum. The additional ultraviolet light was further absorbed by means of Absorban cement layers. This also assured that all lenses maintained the same color transmission, regardless of focal length. Even at full aperture, the residual aberrations were corrected so well that in practice they did not affect the performance even at full aperture.
There were several variations of the Leica R bayonet mount:
- 1 cam - introduced with the LEICAFLEX (Standard); has a single sloped cam that transmits the aperture value to the external exposure meter. 1-cam lenses can be used on SL/SL2 and R-series bodies in stop-down metering mode only and not recommended on R8/R9 because of possible damage to the camera's ROM contacts.
- 2 cam - introduced with the LEICAFLEX SL; has two sloped cams; the second cam transmits the aperture value to the TTL exposure meter. 2-cam lenses are fully compatible with the LEICAFLEX (Standard). On R-series bodies, the limitations are the same as for the 1-cam lenses.
- 3 cam - introduced with the LEICA R ELECTRONIC; has two sloped cams and a third stepped R-cam that transmits both maximum and set apertures to the TTL exposure meter. 3-cam lenses are compatible with all LEICAFLEX and LEICA R bodies.
- R only - only has the third stepped R-cam. R-only lenses were made for LEICA R bodies and will not fit LEICAFLEX bodies.
- ROM - only has the third stepped R-cam plus electrical contacts transmitting the focal length to the body. Even though the data exchange is only supported on the R8/R9 (the information is used in flash metering and also transmitted to the DIGITAL-MODUL-R), mechanically ROM-lenses are fully compatible with all LEICA R bodies. Like R-only lenses, they will not fit LEICAFLEX bodies.