Pentax K-mount
The Pentax K-mount, sometimes referred to as the “PK-mount", is a bayonet lens mount standard for mounting interchangeable photographic lenses to 35 mm single-lens reflex cameras. It was created by Pentax in 1975, and has since been used by all Pentax 35 mm and digital SLRs and also the MILC Pentax K-01. A number of other manufacturers have also produced many K-mount lenses and K-mount cameras.
Mounts
The Pentax K-mount has undergone a number of evolutions over the years as new functionality has been added. In general, the term K-mount may refer to the original K-mount, or to all its variations.Originally designed by Zeiss for an alliance with Pentax, it was intended to be a common lens mount for a proposed series of cameras and lenses. However, the plan failed to work out and the two firms parted company amicably, but Pentax retained the lens mount and at least one Zeiss lens design for its own use.
K-mount
The original K-mount is a simple bayonet connection with three tabs. It was introduced with the K series of cameras. The lens is locked into the camera with an approx. 70° clockwise turn.The only linkage with the camera is mechanical and involves the aperture. A slot between two of the bayonet tabs on the lens allows the stop-down coupler from the camera to sense the aperture setting on the lens and adjust the light meter display accordingly. Opposite this is the diaphragm release from the lens which extends into the camera body and holds open the spring-loaded diaphragm of the lens. When setting up a shot this keeps the diaphragm fully open. When the shutter is released, so is this lever. It allows the diaphragm to close to the desired setting while the film is being exposed, and opens it again after the shutter closes.
Both of these linkages are arranged so that they are aligned and spring-loaded by the act of inserting the lens and turning it until it locks.
Bodies equipped with the original K-mount include the K series, the M series except the ME F, and the LX. Lenses that support it include those labelled 'SMC Pentax', 'SMC Pentax-M' and 'SMC Pentax-A'. These K-mount bodies cannot use lenses that lack an aperture ring, such as FAJ or DA.
K-mount lenses can be used on all Pentax bodies, but are restricted to stopped down mode when used with “modified" KAF-mount bodies.
KF-mount
The KF-mount was Pentax's first attempt at an autofocus system. This autofocus system used sensors in the camera body and a motor in the lens. The two were connected via five new electrical contacts on the bayonet mount itself. One permitted the lens to turn on the camera's metering and focus sensors, two focused the lens and two appear to have been unused and may have been reserved for future functionality.The KF-mount was largely a failure. Only one camera and one lens ever used this mount, the Pentax ME F and SMC Pentax-AF 35-70/2.8. The lens was somewhat large and cumbersome since it had to enclose both the focusing motor and batteries to power it. KF and the ME-F are similar in many ways to the system used by Canon in the ill-fated Canon T80, introduced several years later.
The ME F can use all Pentax K-mount lenses which feature an aperture ring. The 35–70 mm lens can be used on all other Pentax K-mount bodies in manual focus mode, but it must be used stopped down on “modified" KAF bodies.
KA-mount
The KA-mount is derived from the original K-mount. It allows the lens's aperture to be set by the body, and thus permits shutter priority and program auto exposure modes. It was introduced in 1983, and is supported by A-series and P-series bodies; Pentax lenses that support it are marked 'SMC Pentax-A'. It is completely backward-compatible with the original K-mount.The aperture on the lens is set from the body by the same stop-down lever found on the original K-mount, but on KA-lenses this lever is proportional to the area of the aperture opening, rather than the diameter as on previous lenses. This allows the body to easily set a specific aperture, since the relationship to F stops is linear. The lenses add an 'A' setting on the aperture dial, which gives the body control of the aperture. Other, numeric settings are used for manual aperture modes—aperture priority and full manual mode.
Six electrical contacts are added to the bayonet ring. One is slightly recessed and allows the lens to indicate whether the aperture ring is set at 'A' or not. If it is, a pin on the lens extends slightly and makes contact, while if the lens is at any other setting the pin is retracted and does not make contact. The other five contacts are used to encode the lens's aperture range. Each contact on the lens is either conducting or non-conducting, providing a binary 1 or 0, respectively. Two contacts encode the lens's minimum aperture—,, or ; although no Pentax K-mount lens has ever had an minimum aperture, OEM lenses often have. The other three contacts encode the lens's maximum aperture; their meaning is dependent on the minimum aperture indicated by the lens.
KAF-mount
The KAF-mount was Pentax's second and much improved attempt at adding auto-focus to lenses. It adds a small drive shaft to the KA-mount, allowing the body to adjust the focus of the lens. This makes the lenses less bulky than the earlier KF-mount, which had both a motor and batteries inside the lens.It also adds a seventh electrical contact, this one carrying digital information from the lens to the camera. It carries the following information: focal length, distance to the subject, exact absolute f-stop value, and lens size. This information is used to make better exposure decisions, along with the multi-segmented metering that was introduced in cameras using the KAF-mount.
The MZ-30/ZX-30, MZ-50/ZX-50, MZ-60/ZX-60, the *ist series and the K100D/K110D lack the mechanical stop-down coupler/indicator. In these cameras – in aperture priority mode – the aperture is set by a dial on the camera body, and no longer on the lens. Pre-A lenses can only be used in manual stop down metering mode and manual flash mode.
KAF2-mount
The KAF2-mount is the same as the KAF-mount except that it adds two extra power contacts to the inside of the mounting ring and transmits modulation transfer function data through the digital seventh contact. The power contacts were originally used for power zooming. Since the introduction of the K10D digital SLR model, they are mainly used for powering Silent Drive Motor and DC motor lenses.The K10D/K100D Super and later cameras do not have a mechanical stop-down coupler/indicator and thus can only use stop-down metering on pre-A lenses.
KA2-mount
The KA2 is identical to KAF, but lacks the autofocus drive shaft. Another way of looking at it is that it adds the seventh contact for digital information to the KA-mount.KAF3-mount
The KAF3-mount is used on Pentax lenses that solely rely on SDM or DC autofocus motors. It is identical to the KAF2, but lacks the screw-drive autofocus drive shaft. Another way of looking at it is that it adds the power zoom/in-lens autofocus motor contacts to the KA2 mount.KAF4-mount
The KAF4-mount was introduced in June 2016 with the HD Pentax-DA 55-300mm F4.5-6.3 ED PLM WR RE lens. It is identical with KAF3, apart from the missing aperture control lever. Instead, aperture control information is transmitted digitally through the data pin and the aperture is stopped down through a motor built into the lens. It also introduced a new type of autofocus motor, designated PLM or Pulse Motor. At the time of its introduction, the following Pentax DSLR bodies were compatible with the new mount: K-70, K-50, K-S2, K-S1, K-1, K-3 II, with all but the K-70 requiring a firmware update. Also after a recent firmware update the original K3 can use the new mount.K-mount without aperture simulator coupling
All digital K-mount Pentax SLR bodies as well as some lower-end film cameras lack the ability to read the position of the aperture simulator. This means that lenses that lack the lens information contacts introduced with the KA-mount do not support open-aperture metering on these bodies. Instead, stop-down metering must be carried out by pushing the “green button” on the camera before taking a shot. This variation of the mount is commonly referred to as the “modified“ K-mount.R-K-mount
The R-K-mount is a variation on the original K-mount by Ricoh. It supports Ricoh's own implementation of shutter priority and auto exposure modes, similar to the KA-mount but much simpler. The only addition to the original K-mount is a small pin, commonly dubbed Ricoh pin, at the bottom which tells the body when the aperture ring has been set to the “P" setting. The 'P' setting is not compatible with the 'A' setting as the 'P' pin is in a different location than the 'A' contact on Pentax 'A' lenses and the flange on Pentax bodies.The R-K-mount is used on Rikenon P lenses, Ricoh bodies that include the letter 'P' in their model number, and some non-Ricoh lenses. It is compatible with all other K-mount cameras and lenses when in manual or aperture-priority exposure modes, however the extra pin needs to be removed for safe use on autofocus Pentax cameras, as it can otherwise become locked within the autofocus shaft. Lenses locked to the camera body this way are difficult to remove and may require complete dismantling.