Minolta SR mount
See also the category Minolta SR mount for cameras accepting these lenses
The Minolta SR mount is the original bayonet for all Minolta 35mm film SLR camera bodies using manual-focusing lenses. Subsequent MC and MD mounts added increasing communication between lens and camera body.
All generations of lenses for these bayonets are interchangeable between older and newer Minolta manual-focus 35mm SLRs. (There are exceptions, such as: the lenses before 1961 feature a slightly different aperture lever, and thus the automatic diaphragm may not work correctly on post-1961 cameras; later MC/MD tabs may hit the pentaprism housing on one earlier camera.)
The basic design is fairly simple: a three-lobed bayonet mount that locks by twisting the lens clockwise. In terms of internal mechanism, the automatic-aperture SR lenses are similar to the Nikon F-mount in that the aperture linkage is spring-loaded to close the diaphragm when the camera releases pressure on the internal lever. Many competitors' lens mounts, such as Canon FL and FD and most automatic-aperture M42 lenses, have the opposite design, in which the resting position of the aperture is wide open, and the camera pushes on a linkage to stop it down.
Four design enhancements, all forwardly inclusive and backwardly compatible, are:
- SR - 1958-1966: Plain SR-bayonet featuring automatic diaphragm. Lenses are labelled Rokkor (pre-set) or Auto Rokkor (automatic diaphragm)
- MC - 1966-1977: These lenses (often called MC bayonet) added a small tab connected to the aperture ring, which pushes on a rotating ring on MC-capable cameras, communicating the aperture setting relative to full aperture. This mechanism allows full-aperture TTL exposure metering and potentially aperture-priority auto-exposure. Lenses are labelled MC Rokkor.
- MD - 1977-1983: second MD tab added, which allows the reporting of the lens being set to its smallest available aperture, allowing shutter-speed priority auto-exposure. Lenses are labelled MD or MD Rokkor (or MD Rokkor-X in North American markets.)
- X-600 - 1983-1998: X-600 mount reporting the lens maximum aperture design from the lens to the camera body which then engaged different sensitivity auto focus confirmation sensors in the camera body.
SR - The SR models from 1958 to 1967 featured the initial design implementation of the SR bayonet. These were simple mechanical cameras without TTL metering or automatic exposure. The SR-7 was the only one with a built-in CdS meter, mounted on the side of the camera body and thus had the same metering capabilities as the external clip-on meters available for SR-1 and SR-3.
MC - The introduction of the SR-T 101 in 1966 featured a meter coupling between a selected aperture on lens and camera body. The camera had two CdS cells inside the prism and metered the exposure through the lens (TTL). The later X-1 and XE models added an aperture-priority automatic exposure mode, and is also incorporated in X-700, X-500-series, and X-300-series camera bodies and variants (X-7, X-9, and so on).
MD - In 1977, the XD series introduced an additional tab on the lens which reported to the XD-series and later X-700 camera body when the lens was set to its smallest available aperture (f/16, f/22, or f/32), confirming for the photographer (and the camera) that the entire range of lens apertures may be used during auto exposure:
- S (shutter priority automatic exposure) mode on XD models
- P (programmed automatic exposure) mode on the X-700.
However, regardless of MD tab presence, or setting any lens to minimum aperture or not, auto exposure modes function using the remaining range of lens apertures between full open and the set aperture, if any. In other words, auto exposure will use whatever range of apertures the photographer chooses to make available, including the reduced range of an MC or MD lens that is not set to its minimum aperture.
Note that Minolta cautioned that non-MD lens aperture blades my be too sluggish to fully adjust and settle down before exposure, suggesting that MD lenses were optimized for this capability. The XD-series cameras delayed exposure to take a second metering after closing the lens down to taking aperture. The X-700 did not incorporate a delay or second metering.
X-600 - On the 1983 Minolta X-600 camera, intended for Japanese-only distribution, there is also a focus assist and confirmation feature. The Minolta X-600 sensors need a clue from the lens as to the lens's maximum aperture so that the camera body can use its appropriate range of light sensitivities from which to asses subject contrast for judging focus accuracy. There is a tang inside the lens that identifies either
- f/2.8 or larger maximum lens aperture, or
- f/3.5 or smaller maximum aperture.
The lens tang operates a switch inside the body of the X-600. There is no MD Auto Exposure feature on the X-600.
Notwithstanding the subtleties above, colloquially the term "MD mount" is the one most commonly encountered (e.g. in eBay listings). It is among the 35mm SLR lens standards with a shorter flange focal distance, although Canon FD mount measures slightly less. These necessitate a slightly longer lens barrel, meaning that users wanting to use Minolta lenses e.g. on modern DSLRs cannot get an adapter which permits infinity focus (unless the adapter includes optics—a weak teleconverter—which may degrade sharpness). Evidently this has slackened demand for MD-mount lenses, as they remain plentiful and relatively affordable on the used market. This may be of interest to digital mirrorless camera users (where the shallow flange distance easily allows for MD-lens adapters).
Brands of SR mount SLR bodies
- Pearl River