Lens mount
Pentax K mount
Pentax K is the 1975 bayonet that replaced M42 while keeping its 45.46mm register, and it remains in use on Pentax DSLRs today.
- Type
- bayonet
- Flange distance
- 45.46 mm
- Introduced
- 1975, Pentax K2, KX, and KM
- Status
- Still current. Pentax DSLRs such as the K-3 Mark III and KF use the KAF4 evolution of the same bayonet.
About the Pentax K mount
Pentax introduced the K bayonet in 1975 on the K2, KX, and KM bodies to replace the M42 screw mount. It deliberately kept the 45.46mm flange distance of M42 so a thin adapter lets screw-mount Takumars reach infinity on K bodies. The mount evolved without breaking compatibility: KA (1983) added electrical contacts and an A aperture position for program exposure, KAF (1987) added the autofocus drive coupling, and the KAF2, KAF3, and KAF4 revisions added power zoom, in-lens motors, and electromagnetic diaphragm control. Every manual-focus K lens still mounts and meters on current Pentax DSLRs.
The SMC Pentax (1975) and SMC Pentax-M (1977) lines are the manual-focus glass most often adapted. SMC is Super-Multi-Coating, Pentax's seven-layer coating that remains one of the reasons Takumar and Pentax glass resists flare so well. On mirrorless, K-mount lenses need only a plain ring adapter and keep infinity focus everywhere. The one habit to keep is leaving Pentax-A lenses off the A position, which otherwise parks the diaphragm at minimum aperture when no body is telling it what to do.
Aperture control
Automatic diaphragm. Pentax-A and later lenses add an A position on the ring that hands aperture control to the body; leave it off A on an adapter.
Adapting it
Plain adapter ring. Because K keeps the 45.46mm M42 register, M42 lenses also mount on K bodies with a thin adapter and keep infinity.
Pentax K lenses in the catalog
| Lens | Focal length | Aperture | Years | Used value |
|---|---|---|---|---|
| Pentax SMC Pentax 50mm f/1.2 | 50mm | f/1.2 | 1975-1990s | $300 to $800 |
| Pentax SMC Pentax-M 50mm f/1.4 | 50mm | f/1.4 | 1977-1984 | $60 to $210 |
Adapting Pentax K to a modern body
Frequently asked
Can Pentax K lenses be adapted to mirrorless cameras?
Yes. Pentax K has a 45.46mm register, longer than any mirrorless mount, so a plain mechanical adapter reaches infinity on Sony E, Fuji X, MFT, Canon RF, Nikon Z, and L-mount. Plain adapter ring. Because K keeps the 45.46mm M42 register, M42 lenses also mount on K bodies with a thin adapter and keep infinity.
What is the flange distance of the Pentax K mount?
The Pentax K flange distance is 45.46mm. It is a bayonet introduced in 1975 on the Pentax K2, KX, and KM. Still current. Pentax DSLRs such as the K-3 Mark III and KF use the KAF4 evolution of the same bayonet.
How much do Pentax K lenses cost used?
The 2 Pentax K lenses in the LensVault catalog range from $60 to $800 used. The least expensive is the Pentax SMC Pentax-M 50mm f/1.4 at a typical $110. Values are estimates from recent sold listings and dealer pricing, not appraisals.