Pentax 6x7 on the bench.

Pentax 6×7 on the bench.

The Pentax 6×7 (known as Pentax 67 after 1990) is a SLR medium format system film camera for 120 and 220 film, producing images on the film nominally 6 cm by 7 cm in size, made by Pentax. It originally debuted in 1965 as a prototype dubbed the Pentax 220. Since then and with improvements, it was released in 1969 as the Asahi Pentax 6×7, as well as the Honeywell Pentax 6×7 for the North American import market. In 1990, it received a number of minor engineering updates and cosmetic changes and was renamed as the Pentax 67.

The camera resembles a traditional 35 mm SLR camera with interchangeable viewfinder and lens, but is considerably bigger and heavier, weighing 2.3 kilograms (5.1 lb) with the plain prism and standard (105 mm f/2.4) lens. It is perhaps inspired by the 1957 East German 6×6 KW Praktisix and its successor, the Pentacon Six, although the horizontal SLR concept can be traced back to the 1933 Ihagee VP Exakta.

The Pentax 6×7 has a dual bayonet lens mount, and a wide range of interchangeable Takumar and later SMC Pentax 67-designated lenses exist. More than forty years after the original camera introduction a wide selection of lenses is still available, together with the latest Pentax 67II variant.

The following models have been issued:

  • Asahi Pentax 6×7 – the original model, launched in 1969 (first generation)
  • Asahi Pentax 6×7 (MLU) – with a mirror lock-up mechanism, launched in 1976 (second generation)
  • Pentax 67 – with minor cosmetic changes, launched in 1990 (third generation)
  • Pentax 67II – the fourth generation model, launched in 1999

The Pentax 6×7, designated product model number 400XXXX by Asahi Pentax, is similar to any traditional 35 mm SLR camera except in size. The Pentax 6×7 is an electromechanical design and shares much in concept with its smaller 135 format cousin the “Pentax Electro Spotmatic”, however, is not equipped with an internal meter. Users familiar with the diminutive cousins in the 135 format would find the Pentax 6×7 an easy transition due to the layout of the camera. This hefty camera with a general dimension body of 7.25 inches × 4.5 inches × 3.75 inches (18 cm × 11 cm × 9.5 cm), and with the standard prism and 105mm lens, would bring it to 7.5 inches × 5.75 inches × 6.5 inches (18 cm × 14.5 cm × 17 cm).

The most obvious difference with common SLRs is the location of the shutter speed knob being at the left hand top. Other small controls are easily located such as the lens release is on the left side of the mirror housing, the shutter release and film advance lever are located on the familiar right-hand side of the top. Because it uses 120 film, there is no provision for manual rewinding of film, as there would be for 35mm film cameras.

At the front of the mirror housing is the pentax 6×7 dual lens mount that allows for both “inner” as a familiar 3 flange proprietary arrangement and “outer” four flange symmetrical arranged bayonet. The latter (outer) was provided for use with larger and heavier telephoto lenses and allowed the body to rotate and lock in any of the four positions. Because of the rotatable mounting, an “outer” mounted lens would not have “automatic aperture” linkage rendering the use of the aperture as a stop-down method of operation.

Another versatile feature is the removable prism. By pressing in the two locking buttons on either side of the finder bay, access allows for an assortment of finders that can be fitted into the bay.

As naming conventions implies, the 6×7 indicates that this is a medium format camera and the negative produced is 6 cm by 7 cm (actual format 56 mm × 70 mm), and additionally the successors 67 and 67II remain the same format. The Pentax 6×7 has the ability to use either the 120 or 220 roll film, which produces ten or twenty frames respectively (twenty-one for the 1969 version). A film roll format selector on the right-hand of the camera permits quick selection between 120 and 220 format film. Additionally, a change to the setting of the film selector must also be reflected in a change to the 120 or 220 position of the film pressure plate. The pressure plate also maintains film flatness in this horizontal design during exposure, aiding sharpness across the entire image. Other systems use film tension alone, or against rails at the film’s edge, in more compact vertical-feed magazines found in 6×6 or 6×4.5 formats.

The standard Pentax 6×7 outfit comprises the Super Takumar and later the Super Multi-Coated Takumar/6×7 105 mm f2.4 and the pentaprism finder that allows for the through-the-lens actual image (90% of actual area) of what is being composed.

The camera is completely battery dependent. Power is provided by a 6 volt PX28 (originally Mercury-specified 1968, and Silver Oxide 1971), but equal substitutes PX28S/4SR44.

As with many systems of the era, the mirror and cloth curtains are mechanically-driven, the timing of the shutter being electrically governed by transistors and a magnet. The combination of resistors routed by the speed setting determine the length of time the magnet remains engaged.

The large cloth curtains as well as the size of the exposure area limits the maximum flash synchronizing speed to 1/30th of a second. Also, the operation of the shutter is not normally possible without film being loaded. However, one can test the shutter by rotating the counter dial away from the empty position while the film door is open and then by closing the film door while still holding the dial, thus facilitating the unlocking of the advance mechanism and operation of the shutter. It was also possible to check the shutter with a bypass key that was inserted in the frame counter engagement slot and allow for inspection of the shutter while the film door was open.

The frame counter is incremented only while there is film passing over the “main roller” or “counter roller” next to the take-up spool in the camera. The camera disengages the “transport system” when the counter dial (connected to the frame counting control cam) has reached the last frame, or when the counter has returned to the “empty” or start position. The automatic frame counter resets only if the shutter is released before opening the back.

Because of the electromagnetic operation of the shutter, a battery is required to power the timing as well as the holding of the curtain release mechanism when the release button is pressed. When there is a loss of adequate voltage, the camera cannot complete the operation cycle. In this state, the mechanically actuated mirror is allowed to rise, however, the curtain release mechanism would continue past the cycle and not fully disengage the curtains from the primed position. Therefore, the reset procedure will be necessary to bring the mirror back to finish the cycle. A small button located flush on the right-hand camera front, just below the shutter-release button, is provided for restarting of the mirror/shutter cycle and depressing the shutter release once more will release the cycle. In a situation where the shutter fails to fully operate, the frame is lost.

The shutter release button is standard threaded for pneumatic bulb/cable releases, an accessory timer or the use of a larger accessory (‘soft touch’) button.

The fingernail-operated latch to the left lower side releases the film door for loading. The film spools are secured by the pins and slot shaped opening at either end of the film spool. The camera has two twist-lock cams that turn and pull out to open, the left side for the unexposed roll and the right side, known as the “take-up” spool. Because of the arrangement differences of the 120 and 220 start length of paper, the indicated starting points are marked above the film plane for lining-up the START mark on the film.

The film advance system is a tension/friction type, the film source side being a tension brake and the take-up side torque/slip clutch.

A counting cam governs the frame count and interacts with the friction system to allow enough slip and movement to accurately space each frame from the beginning of the roll to the end. The counting cam also allows the system to regulate a lock to open and close, allowing the shutter to fire. This slip system has brought criticism of durability in early models, as it would slip more over time, causing frame spacing issues as well as disengaging the shutter. The frame counter system, tied to the counter roller, operates the automatic reset of the counter (i.e. returns it to start) whenever the back is opened, and also sets the regulating of the next frame.

Pentax has one of the widest range of lenses available for a medium format camera. The first generation of lenses available had a standard multi-coating and were named “Super-Takumar.” After the release of the improved 7-layer coating, they were labelled “Takumar Super-Multi-Coated”. Later lenses would abandon the Takumar branding in favor of “SMC Pentax 67” and include modifications to optics, functional and cosmetics.

Most of the lenses are “Auto-Aperture” type to allow for the brightest viewing and focusing of the lens for composition of the subject. The lens also has an aperture tab that couples to the indexed sliding ring found under the mount ring of the body. In turn the ring has a chain connected and running up into the finder bay and linked to a tab under spring tension. Operation of the aperture ring would operate the ring and feed the chain back and forth to move an indexing tab. This was only utilized by the TTL meter prism, and was not needed for any other finder available.

The exceptions for “Auto-Aperture” or aperture linkage are: The 75 mm Shift due to the manner that the base must slide out of direct alignment to the forward elements that the linkages for the Auto-Aperture is not possible. The 120 mm Soft Focus due to its dual aperture system. The 600 mm and 800 mm due to their “rack and pinion” focus that it is not possible to have linkages to the Auto-Aperture. The 1000 mm being a catadioptric lens that it is not possible to have an aperture.

Two leaf-shutter lenses were made available. The 90 mm f/2.8 and 165 mm f/4 permitted flash sync at all speeds, thereby solving many mirror and shutter vibration problems, as well as allowing for fast shutter speeds for use with strobes and portable flashes while in bright shooting conditions where the 1/30sec synchronization speed is not ideal. Lenses are linked to the body by the operation of the aperture stop-down lever being tripped. The operation of the leaf shutter requires the camera’s native focal plane sync speed of 1/8 second to be set in order to synchronise correctly with the lens leaf shutter. Mirror lock-up, on cameras so fitted with this function, can be used in leaf shutter mode with the 90 mm LS lens, but should not be used with the 165 mm due to mechanical differences with the risk of jamming and damage to the camera. With either leaf shutter lens set to LS mode, the TTL meter on the Pentax 67 will not operate.

The through-the-lens (TTL) metering pentaprism viewfinder included a knurled shutter dial ring with fitted case. The TTL-metered pentaprism is the same coverage as the non-metered pentaprism, a coverage of 90% of frame and has a sensitivity pattern of 60% center-weight and 30% inner field sensitivity. The TTL Metering Pentaprism has no internal power of its own, instead, the operating power comes from one of the three contacts found in the finder bay of the body as well as grounding to the body. Only two of the three contacts are utilized and depending on the two modes: Normal as ‘AUTO’ mode and in an override to stop-down mode in the ‘MAN’ mode as found on many equipped lenses. The TTL metered prism has a 5-stop exposure range.

In ‘AUTO’, the lens is fully opened and adjustments are read from the coupled index from the lens—through the index ring of the body mount—to the chain and index shuttle, the TTL meter receives the position information via a protruding tab facing the finder bay. The tab operates a linear potentiometer.

In ‘MAN’ or manual mode with so equipped lenses, the sliding of the lens switch will move an internal lever that then presses down on the activating switch in the body. The switch is located inside the pin of the lens release pin. This inner pin is connected to an electrical toggle inside the body and switches the current from body grounded to bay connector to activate the secondary circuit.

The physical difference of the TTL meter to the regular prism is the coupling arm that extends to the shutter speed dial. The dial covers the body shutter speed dial and is coupled via a spring loaded index pin. The included knurled ring assists with the operation of the shutter speed dial which is otherwise difficult to operate by itself with the prism in-situ.

The stop-down mode or direct metering while the aperture is allowed to operate and change the amount of light is similar to the ‘MAN’ mode, but activates when a non-auto-aperture lens is mounted causing index ring to be positioned to place the meter’s linear potentiometer into a bypass mode to activate the secondary circuit in the meter. The lens is allowed to stop-down and the light is directly measured, however, the shutter speed dial link operates the same in ‘MAN’ mode.

As with the body receiving improvements over time, so did the TTL meter have some changes. Although the image coverage remained unchanged, the type of metering and the circuitry received some upgrades. CdS (cadmium sulfide) to Gpd (gallium photo diode) photo cells and a two part circuit to a single board improved response time and reliability. The early version is identified by the single marked ‘On’ switch and the meter needle starts from up to down and the later model has a ‘On’ and ‘Off’ marked switch and the meter needle starts from bottom to top. The later model would also have the sole “Pentax” badge by 1986.