Pentax 6×7

Description

The Pentax 6×7, designated product model number of 23400 by Asahi Pentax, is similar to any traditional 35mm SLR camera except in size. The 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 × 6.5inches / 18 cm × 14.5 cm × 17 cm. Users familiar with the diminutive cousins would find the Pentax 6×7 an easy transition due to the layout of the camera. Differing only in the location of the shutter speed knob as it is located on the left hand top. Location of the lens release is on the left side of the mirror housing, the shutter release and film advance lever are located on the right-hand side of the top. 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 56mm X 70mm) 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 respectively (twenty-one for the 1969 version). A small slotted selector on the right-hand side next under the film advance lever of the camera selects the film type (properly operated when film door is opened prior to selecting), and also the film pressure plate inside has positions for either type, the thickness of the films being different as it passes the 'main roller' towards the 'take-up' spool. The pressure plate also maintains film flatness in this horizontal design during exposure, aiding the extreme sharpness across the entire image for which the camera is renowned. 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 synonymous or standard equipment includes the Super Takumar and later the Super-Multi-Coated TAKUMAR/6×7 1:2.4 f=105 lens and the pentaprism finder that allows for the 'through-the-lens actual image (90% of actual area) of what is being composed.

Mechanical details

While the camera is almost completely battery dependent (small exception)—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 capacitors routed by the speed setting determine the length of time the magnet remains engaged. Also, the operation of the shutter is not normally possible without film being properly 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. The frame counter is incremented only while there is film passing through 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 a battery must power the timing, the loss of adequate voltage means the camera halts after the mirror is allowed to rise, and therefore the curtain release will not disengage. To drive the mirror 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. Depressing the shutter release once more will release the cycles. The shutter release button is standard threaded for bulb or cable releases or the use of a large accessory 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 to the 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”. 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 of the start marks for 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 (returns it to start) whenever the back is opened and also sets the regulating of the next frame.

Later improvements

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 rubberized Counter Roller for a smooth metal roller, the 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 6x7 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 control the induced camera vibrations caused by the upward movement of the large mirror to a sudden stop, 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 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-up or 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 1990.

Lesser known for the later original 6×7 was a special factory modification that would allow the bypassing of part of the frame counter mechanism (Duality-Prevent lever) for deliberate double exposures, though not many were made with this feature have been reported. (Not verified)...this modification may have often found on 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 force the shutters to lock open and release by simple using two cable releases.

Polaroid Back/Foscher adapted bodies were a non-factory modification and was usually applied by authorized service centers. A familiar tool for studio photographers for lighting tests. There would be later versions of this modification to give users an ability to make both back interchangeable for users. This special modification allow 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 reattaching the leatherette.

Other changes were to the frame counting cam that shorten the 220 film frame count from 21 to 20 and the 120 mode remained the same. This reduction was necessary as the new version of the 'clutch' plate to improve durability was released. This change also tied to the switching from rubberized "Counter Roller" to an all-metal smooth version.

A minor change of color lens release switches from chrome to black as found on the 67 model (designated model number of 22401). Due to these changes over time, some reports of mixed and matched factory release bodies also existed as well as mix matching as a result of authorized servicing mandating the exchange of the older advance system for the newer version.

Lenses and accessories

A wide range of lenses is available for this camera. The first lenses made available had a standard multi-coating and named "Super-Takumar", and, after the release of the improved 7-layer coating, they were first known with the engraved "Takumar Super-Multi-Coated" and eventually the latest would abandon the Takumar in favor of Pentax and consolidate the coating name to SMC. Most of the lenses are "Auto-Aperture" type to allow for the brightest viewing and focussing of the lens for composition of the subject. The "Auto-Aperture" linkage of the lens couples to the indexed sliding ring of the body. In turn the ring has a chain connected and running up into the finder bay and linked to a spring. 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" are: The 75mm 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 120mm Soft Focus due to its dual aperture system. The 600mm & 800mm due to their "Rach and Pinion" focus that it is not possible to have linkages to the Auto-Aperture. The 1000mm being a catadioptric lens that it is not possible to have an aperture.

Two leaf-shuttered lenses were also made available, first the 90mm 2.8 and later a 165mm 2.8 that both allowing 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.

The through-the-lens (TTL) metering pentaprism viewfinder and included a knurled 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 stopdown mode in the 'MAN' mode as found on many equipped lenses. In 'AUTO' is where 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 a electrical toggle inside the body and switches the current from body grounded to bay connector to activate the secondary circuit. The installation of the TTL-Meter into the finder bay requires first the removal or turning of the lens to remove tension on the aperture chain. When the lens is rotated to allow the index on the chain to properly match up with the tab under the meter, the finder can then be seated and firmly pressed until the locks on either side of the finder latch. Removal of the finder is the reverse by first removing the lens and then pressing in the locks on the sides of the finder and lifting out. The physical difference of the TTL-Meter to the regular prism is the bulky arm that extends to the shutter speed dial. The dial covers the body dial and is coupled via a spring loaded index to the shutter speed dial. The included knurled ring assists the reach of the shutter speed dial due to the bulk of the TTL-Meter prism. The stop-down mode or direct metering through 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 potenioment 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 did the body receiving improvements over time, so did the TTL-Meter have had 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 to improve 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' & 'OFF' marked switch and the meter needle starts from BOTTOM to top. The later model would also have the sole PENTAX badge by 1986.

Two waist-level finders are available; a collapsible model that compactly folds almost flush with the top of the body and a fixed or rigid finder often called the Chimney finder. Both finders provided a 100% view of the frame. A special viewfinder was available as well for the Pentax 6x7 Marine Housing for use in underwater applications.

Along with the standard micro-prism center focusing screen, four other focusing screens are available and could be refitted into the body (plain, grid, grid with micro-prism, split-image as well as the standard). Due to the fact that the installation of a screen required a qualified technician and then re-calibrate the new screen the camera, it is rare to find screens other than the standard version. The micro-prism screen is adequate or usable down to f4.5 lenses, however, the more desired split screen is capable of operating down to f5.6 before the center going black.

Another separately available accessory is the distinctive left-hand grip with accessory shoe. Many manufacturers offer accessory grip or "action grips" such as Kowa, Bronica, Mamiya and Hasselblad the Pentax grip is arguably an iconic accessory for the camera. It attaches to the two lugs/posts at the front of the camera and is secured by tightening a finger-operated bolt onto a stud found at center. The grip is removed by untightening and lifting the bolt to slide off in a downward direction to allow the lugs to clear the keyhole slots.

Quick-focus ring A & B were first list in 1971 for use with the two most common diameter focusing barrels ranging from 35mm to 200mm.

Magnifier is designed to be fitted under the eyepiece holder by the means of a metal plate under the rim of the eyepiece.

Rigid bayonet hoods were available for many of the lenses from 45mm to 200mm.

Pentax 6×7 lenses feature the ability to accept both standard threaded filters and also Pentax bayonet filters that are available in standard and SMC versions.

Pinch-on hoods were introduced at about the same time as the released of updated 6x7 lenses started to wear the 67 engraving. Some lenses would be offered the hood while most was an option.

Cold-weather battery holder was available from 1969 and minor changes were applied to the appearance. The cold-weather battery holder allowed the relocation of the battery by using a long cord with a dummy battery carrier and receptacle for the original battery holder to then be placed in a warm pocket to avoid battery failure due to cold.

Along with the availability macro lenses for close work, a selection of extension tubes and in both the standard bayonet and the outer bayonet were available as well. As well as a compact and convenient variable extension was also available. For more flexibility a bellows system was available as well as a slide copier accessory.

List of lenses

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

♣ Older/original version (pre-updated optical design); ♦ Also existing as first release version, Takumar (non-SMC or pre-SMC)

Wide-angle

Standard

Telephoto

Special Purpose

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

Zoom lenses

Tele converters