K-Mount Evolution, Features and Operation

The term “K-mount” has two meanings:

• Strictly speaking, it refers only to the original K-mount, as introduced in 1975 by Pentax.
• More commonly, it is a collective name for all mount variations: from the 1975 original through the ones that are in production today.

The main reason for this double meaning is Pentax’s devotion to the K-mount — during the years they have extended the mount’s functionality with automatic exposure, auto focus, digital information exchange and other features but usually retaining compatibility between older and newer equipment. In fact, if we exclude the bodies and lenses featuring the K_F and the “crippled” K_AF mount, combining any body with any lens produces a correctly-operating combo that possesses all features common to both pieces of equipment. Bodies and lenses featuring the K_F mount are fully-compatible with each-other as are the bodies and lenses featuring the “crippled” K_AF mount.

Along with all positive effects of the mount’s evolution, there is also a negative to cope with — a serious naming confusion. Not only did Pentax change the equipment names every time they introduced a new mount variation, they also gave inconsistent names to each variation and its corresponding bodies and lenses. Thus it is a bit difficult to know immediately which lenses match the features of which bodies, and which mount variation is represented by which equipment. Furthermore, like other companies, Pentax sells identical equipment under different names in different parts of the world. For example, the PZ-series camera bodies sold in the USA are identical to the Z-series sold in the rest of the world. The same holds for the ZX- and MZ-series bodies. The exact reasons for this double-naming scheme are not known, but the following have been suggested: some names are offensive in some languages; certain names work better in certain languages; different names help distinguish grey-market items; different names help customs officers identify taxable equipment.

The following documents explain every mount variation in detail. The mounts are presented in chronological order, and each document assumes familiarity with all previous ones. The diagrams are courtesy of Dario Bonazza.

Manual-focus mount-variations: K, K_A, K_A2
Auto-focus mount-variations: K_F, K_AF, K_AF2, “crippled” K_AF, “crippled” K_AF2