Pentax 6×7

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 105 mm 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 35 mm 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 the name implies, the 6×7 is a medium format camera and the negative produced is approximately 6 cm by 7 cm (actual format 56 mm × 70 mm, aspect ratio 5:4 = 1.25 ), and additionally the successors 67 and 67 II remain the same format. The Pentax 6×7 is able to use either the 120 or 220 film rolls, which produce 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 match a change to the 120 or 220 position of the film pressure plate: The pressure plate keeps the film flat during exposure, aiding sharpness across the entire image (when the lens focal plane is also flat). 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 f/2.4 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.

Over time the problematic advance mechanism was modified to increase reliability of the overall transport system. A phasing in of key replacements such as the replacement of the rubberized Counter Roller for a smooth metal roller, the internal Transport Control Wheel was replaced to reduce the number of frames and also requiring the Counter Control Cam to be replaced at the same time. The introduction of the improved parts also meant the ceasing of original first generation parts, inventory of stock parts would quickly become exhausted and the newly issued non-backward compatible of the parts would make remaining unmodified bodies requiring full upgrades to continue working. The improved parts would become standard replacements after the early 1974 for bodies coming in for servicing of the transport mechanism and would later be summarized and identified by the issuing of the parts catalogs in late 1974 and 1975 in the fall of 1986 for the Pentax 6×7 service bulletin as well as standard parts in the introduced 67 version launched in 1990.

Changes to the advance lever angle from a tipped out to a curled inward and the trim shroud at back of the finder bay had a matching scallop for the new lever design to rest upon, this appeared about late 1972. As well were changes to the spool release mechanism, where it was an improvement from a checkered friction operated surface to a more convenient flip handled method and the center posts that held the film spools lost their angled profile for a more controversial straighter angle that improved film feed accuracy, but caused some difficulty in speed of spool placement during film reloading and also to prompted some to seek services to custom grind the posts.

In 1976, to address the issue of induced camera vibrations caused by the 6×7's large mirror swing and suddenly stopping, a mirror release mechanism was introduced. By sliding upwards the mirror-up switch on the right hand side of the mirror housing, it allowed a bypass of the mirror release from the shutter trip cycle. This allowed the mirror to fully raise and then hold, allowing then the shutter release cycle still be separately at the ready. Unfortunately, this also activated the main power switch that was mechanically tied to the mirrors' main gear action and until the depressing of the shutter release to completes the exposure, the power to the circuits remain on and would drain the battery over time. Even with this one negative aspect to the mirror lock-up modification, it would still become a standard feature in later productions.

The introduction of the mirror lock-up (MLU) feature appeared at about the same time as other critical changes, as with the counter components and other key components in the advance mechanism. Pentax slowly phased out the parts compatible with the first released version, in favor of improved and more durable parts. The exhausting of parts also meant that later new production bodies had all the new parts installed at the factory and would later become standard in the 67-badged models officially by and after 1990.

Other changes were to the frame counting cam that shortened the 220 film frame count from 21 to 20 exposures, but the 120 mode otherwise remained the same. This reduction was necessary when the new version of the 'clutch' plate to improve durability was released. The change also tied to the switching from rubberized "counter roller" to an all-metal smooth version.

Lesser known for the later original 6×7 and 1990-era 67 cameras was a special factory modification that would allow the bypassing of part of the frame counter mechanism ("duality-prevention lever") for deliberate double exposures, though not many were made with this feature, and estimate of only a few hundred may exist. The camera could also be returned to a Pentax service facility to have the multiple exposure facility installed at owner's expense. That modification may often be found on some Polaroid/Foscher-equipped bodies.

Another modification was a non-powered bulb exposure. This was a popular request from astronomers that needed the camera to expose for times greater that the batteries could allow. The demand for this modification was reduced when the availability of a third-party adapter plate that could override the need for a battery, and mimic the cycle of the mirror release and shutter opening by a simple plate that employed two shutter release cables.

Polaroid back / Foscher-adapted bodies were a non-factory modification that was usually applied by authorized service centers, and was a popular enhancement used by studio photographers for lighting tests. There would be later versions of this modification to give users an ability to make both backs interchangeable. The special modification allowed switching in, out of the Foscher back, to a normal pressure plate for roll film without the need for a service technician to partially disassemble the hinge, as well as re-attaching the leatherette.

A minor change of color to the lens release lock from chrome to black is found on the 67 models (designated model number of 22401). Some reports of mixed-and-matched part factory release bodies also existed, as well as mix / match as a result of authorized servicing mandating the exchange of the older advance system for the newer version.

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 lens 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.

Listed below are current and earlier lenses (as indicated) for the cameras as of November 2011.[7]

Wide-angle

SMC Pentax 67	45 mm	f/4
SMC Takumar 6×7	55 mm	f/3.5	◊ ※
SMC Pentax 6×7	55 mm	f/4	◊
SMC Pentax 67	55 mm	f/4
SMC Pentax 67	75 mm	f/2.8	AL
SMC Pentax 67	75 mm	f/4.5

Standard

SMC Pentax 67	90 mm	f/2.8
SMC Pentax 67	105 mm	f/2.4	※

Telephoto

SMC Takumar 6×7	150 mm	f/2.8	◊ ※
SMC Pentax 67	165 mm	f/2.8
SMC Takumar 6×7	200 mm	f/4	◊ ※
SMC Pentax 67	200 mm	f/4
SMC Pentax 67	300 mm	f/4	◊
SMC Pentax 67	300 mm	f/4	ED IF M*
SMC Takumar 6×7	400 mm	f/4	◊
SMC Pentax 67	400 mm	f/4	ED IF
SMC Pentax 67	500 mm	f/5.6
SMC Pentax 67	600 mm	f/4	※
SMC Pentax 6×7	800 mm	f/4	◊ ※
SMC Pentax 67	800 mm	f/6.7	ED IF
SMC Pentax 6×7	1000 mm	f/8	Mirror

Special purpose

SMC Pentax 67	Fish-Eye	35 mm	f/4.5
SMC Pentax 6×7	Shift	75 mm	f/4.5
SMC Pentax 6×7	LS	90 mm	f/2.8	(leaf shutter)
SMC Pentax 67	Macro	100 mm	f/4	SMC Life-Size Converter
SMC Pentax 67	Soft	120 mm	f/4
SMC Pentax 67	Macro	135 mm	f/4
SMC Pentax 67	LS	165 mm	f/4	(leaf shutter)

Extension tubes for macro photography

Pentax	Helicoid Extension Tube
Pentax	(Auto) Extension   1, 2, & 3
Pentax	Extension (outer)   A, B

Zoom lenses

SMC Pentax 67	55–100 mm	f/4.5
SMC Pentax 67	90–180 mm	f/5.6

Teleconverters

Pentax 67	Rear Converter	1.4×	†
Pentax 67	Rear Converter	2×	†
Pentax 67	Rear Converter	T5 1.4	‡

Legend
◊	Older/original version (pre-updated optical design).
※	Also existing as first release version, Takumar (non-SMC or pre-SMC).
†	Not usable with the SMC Pentax 67 165 mm f/4 leaf shutter lens.
‡	Only for 800 mm telephoto.
AL	Aspherical Lens
ED	¿ ?
IF	¿Lens-internal focusing?
M*	¿Macro focusing feature?

• "Pentax 67 II home page". Ricoh Imaging. Japan.
• Krasnov, Sasha (1 September 2016). "Mirror stuck repair in Pentax 6×7 & 67 cameras [instructions]". Sasha Krasnov Photography (skrasnov.com). Pentax 67.
• "Repair of broken Pentax 6×7 / 67 TTL meter aperture-coupling chain". salzgeber.at. Austria.
• Hendrickson, Eric. "Repair of Pentax 6×7 / 67 cameras". pentaxs.com. Knoxville, TN.

Media related to Pentax 6×7 at Wikimedia Commons