Konica's AR mount

From the outset, Konica’s engineers designed the AR mount as a platform to host a fully-automatic exposure control system coupled with full-aperture TTL metering. Konica’s initial bayonet mount – developed in the late 1950s and called the ‘F-mount’ – was ill-suited for such a system because its diameter (Ø = 40,5mm) was far too narrow to accommodate the necessary couplings. In order to enable fully-automatic exposure with full aperture metering, Konica needed an entirely new lens mount and was the first SLR maker to build one with AE operation in mind. The new mount – the ‘AR mount’ (Ø = 47mm) – was the element around which a whole new SLR system was conceived.

The AR-mount turned out to be one of the most successful designs in the industry. It has several characteristics which don't appear together on most SLR lens mounts and which make it technically very stable and ‘user friendly’. Those characteristics are:

1. A relatively large diameter, which assures stability between lens and body,

2. The angle of rotation required to lock the lens in place (~60°) is neither too narrow nor too wide,
. The design of the mount’s release mechanism allows for easy single-hand lens changing,
. The coupling tab and cam are found within the mount's throat, without protrusions on the lens barrel.

Taken together, these traits can only be found on Olympus' OM mount. That mount, however, was introduced in 1972 and remained strictly manual, for Olympus never introduced a SLR with shutter-priority AE capability.

When the Konica’s AR-mount it was introduced it was arguably the industry’s most advanced lens-to-body coupling mechanism: On the lens side, it has a indexing flange next to the aperture-actuating cam of each automatic Hexanon AR lens. With the introduction in 1965 of the Auto-Reflex, a camera without TTL metering, this flange served no other purpose than to shield the aperture-actuating cam from physical damage. But with the introduction in 1967 of the Autoreflex T, Konica’s first body with TTL metering, this flange was provided with a cut-out whose length on any given lens corresponded to that lens’ maximum aperture value.

On the camera side, at the bottom of the mount there is a lever coupled to the camera’s automatic exposure system. As the lens is mounted on the camera, its indexing flange engages this lever and the extent to which it is shifted is determined by the length of the cut-out on the lens’ indexing flange. In this manner the camera's automatic exposure system is set to the largest aperture opening of any lens.

Other makers devised similar indexing mechanisms. Minolta's tab on the aperture ring and Nikon's "rabbit ears" served the same purpose, but were located on the outside of the lens barrel. Canon and, in due course (1975), Pentax, placed their indexing tabs within the mount 's throat. In the case of all those makers, such mechanisms were coupled to the camera’s light meter. What was different with Konica is that its indexing mechanism coupled the lens to the camera’s automatic exposure system and calibrated that system for AE operation with the lens mounted on the camera.

The Konica AR lens-to-body coupling mechanism makes for a highly-flexible exposure management system that allows the user to choose between three exposure modes, all based on full-aperture TTL metering:

1. Manual aperture priority (the user turns the shutter speed dial until the needle in the viewfinder points to the desired aperture value,

2. Manual shutter priority (the user chooses a shutter speed then, using the lens' aperture ring, lines-up the needle in the viewfinder with an index mark, and
. Fully automatic shutter-priority exposure (the user chooses a shutter speed and the camera’s AE system selects the appropriate aperture value).

Just how advanced Konica’s AR-mount was at the time can be seen in the fact that it was the only mount among the big-six OEM mounts which provided shutter-priority automatic exposure using automatic lenses and which remained unchanged until 1988. With the exception of Olympus – the only SLR maker whose lens-mount remained unaltered for the duration of the OM system’s production – all of Konica’s principal competitors had to upgrade their mounts when they decided, in the second half of the 1970s, to offer shutter-priority exposure. Most went through several such upgrades:

Canon - FL (1964-71), FD (1971-79), and New FD (1979-87),

Minolta - Pre-MC (prior to 1969), MC (1966-77), and MD (1977-85),
 - F (since 1959), AI (1977-83), and AIS (from 1983), and
- M42 (until 1975), K (from 1975), and KA (from 1983).

When Konica introduced its first TTL metering SLR in 1967 with the Autoreflex T, all the elements necessary to take advantage of this feature and integrate it with the automatic exposure system had already been part of the AR-mount for 3 years. As a result, all Konica AR-mount lenses except the very first ones made for the Auto-Reflex, which did not have TTL metering, are fully functional on all Konica SLRs made from 1965 to 1985. After the introduction of the Autoreflex T in 1967, Konica modified all the earlier lenses free of charge so they could be used in TTL mode on the Autoreflex T and subsequent Konica SLRs. The modification in question consisted in replacing the flange on the back of the lens with one that had a notch of the appropriate length. As lenses of this vintage that have not been so modified are quite rare, the issue of backward or forward compatibility between various Konica AR bodies and lenses is virtually non-existent.