The Pentax LX  Index Publications
Late in 1979 the Pentax LX camera system was released in-line with the 60th anniversary of the founding of Asahi Optical Co. Ltd., Pentax Corporation's parent company. The Pentax LX System was well publicised at its release and drew instant accolades however over the following decade its market profile faded, due in part to scant advertising, ill timed complementary lens releases and the introduction of "full-program" auto exposure and auto-focus camera systems. In appreciation of the continued popularity of the LX Pentax released (Japan only) the LX Titanium with metal parts clad in a chrome coloured titanium finish and leather body covers, in 1994, 1000 were made, then in 1996 they released the LX Limited (Japan only) with black titanium body panels with the word 'Titanium' engraved below the shutter speed dial and leather body covers, only 300 of these were made. In defiance of the competition the Pentax LX apparently still remains available in Japan, however most Pentax distributors external to Japan (excluding Germany) generally claim that the LX is no longer available. The Pentax LX was Pentax Corporation's realisation of a professional 35mm camera system using their accumulated knowledge combined with the best available technologies; it is a robust full-frame 35mm single lens reflex design and the lightest, most compact camera system in the Pro 35mm class. It offers automatic or metered manual exposure; TTL integrated flash and an exceptionally wide metering latitude provided by an accurate "real-time" direct off-the-film metering system. The ability of Pentax to design robust compact systems was epitomised in the austere stylised design of the LX which provides superb balance, ease of handling and low vibration operation. The LX system peripheral components are modular and faithfully extend the body design rationale. Pentax boasts that the LX offers high reliability and provides environmental resistance to dust and moisture and tolerance to temperature extremes due to the implementation of specialised construction materials and techniques, including gaskets, foam seals and sealed ball bearings at all susceptible junctions. The physical construction of the Pentax LX is based on a light but durable die-cast machined aluminium alloy chassis featuring a removable prism system. Other notable features are the rugged film transport and precision titanium horizontal run Electro-mechanical shutter that provides limited shutter operation in the event of battery failure. Index Body: The precision-machined chassis of the Pentax LX is finished with a black alumite coating or brushed titanium while some areas of the body are clad with vinyl or leather trim (depending on the version). The LX features a removable prism system, mechanical access ports and electrical contacts for peripherals such as data backs, bulk film back, compact motor drive and winder with power pack options. The LX body is fitted with three well anchored special accessory lugs (similar to those on the Pentax 67 and 645) provided to facilitate the attachment of various combinations of quick release carry straps and auxiliary grips. The positioning of the accessory lugs allows for vertical or horizontal attachment of the carry strap and the design of strap lugs allows unimpeded strap rotation. The Pentax LX uses a "K" type bayonet lens mount therefore providing compatibility with a wide range of lenses from pre and post 1980. The body weight including the standard FA-1 finder is a meagre 565 grams and remains amazingly small even when housed in the Pentax LX soft case. The Pentax LX houses a precision horizontal run electro-mechanical shutter which provides limited but entirely mechanical shutter operation from 1/75s to 1/2000s and has been engineered to provide resilience to extremely low temperatures. The shutter is constructed of two extremely thin, flexible, black coloured titanium foils which are almost "paper like" in appearance. The film transport mechanism employs ball bearings and the proven Pentax Magic needle film-loading system on the film take-up spool. When loading a film the shutter dial is best set to a high manual shutter speed otherwise the auto-exposure system may select a lengthy shutter speed making advance to the first frame cumbersome. A multiple exposure mechanism and precision two-way additive film counter allows the film to be wound back to any frame with some registration accuracy (there is an audible click per frame during film rewind), the two-way counter text is marked in red at each standard film length and has frame markings through to 38 frames. All optical surfaces in the viewfinder system (excluding the reflex mirror and finder screen) have been subjected to the exclusive Pentax SMC coating process providing optimum contrast and visibility. The viewfinder provides shutter speed and mode information down the right side of the window via coloured LEDs and reflective text printed on the condensing lens, manual shutter speeds and exposure mode are indicated by a translucent blue flag which can be seen behind the text. A translucent red flag visible at the top right edge of the frame indicates that exposure compensation is active but does not indicate polarity of the exposure compensation. Several finders also provide a view of the lens aperture selection at the top of the finder screen (aperture information is not available regardless of the prism in use if extension tubes, tele-convertors, bellows or medium format adaptors are in use). The shutter speed text and meter LEDs are difficult to see if the prism is removed for overhead viewing whilst in a brightly illuminated environment and when in a very dark environment the text can not be seen (unless light is available to illuminate the reflective text through the rear of the finder). However the LED meter colours provide a vague indication of exposure status, red for over and under, yellow between 4 and 1/15 seconds and green between 1/30 and 1/2000 seconds. The top deck houses most of the controls, there is a rotary dial for the film speed setting and the exposure compensation, a lock is provided to prevent the film speed from being changed accidentally. A small combination lever and button are used to release the prism and to enable exposure compensation respectively and in some bodies depressing this button also enables the light metering system. The shutter button and lock are quite conventional, the shutter action is smooth and satisfying, partially depressing the shutter button enables the metering for a short period. The shutter lock takes the form of a rotating collar surrounding the shutter button that is easily disengaged via a flick of the poised shutter release finger. The rapid wind lever is a 120-degree single stroke design with a 25-degree stand-off position. The film advance action feels smooth, light and positive. The other main control item is the Multi-function lever; it is a short black plastic wedge with a button in its centre mounted on the front of the body beneath the shutter. It provides a variable self-timer function (can be set from 4 to 10 seconds delay), Depth of Field preview and mirror lock-up which significantly reduces reflex mirror induced vibrations. Normally under limited use the paint on the Multi-function lever release button invariably peels away to reveal bare brass. The self timer and mirror lock functions cannot be used simultaneously. Exposure System: The Pentax Integrated Direct Metering (IDM) system controls the shutter opening period during the actual exposure "real-time" by integrating the volume of light reflected off the film and closing the shutter when it has determined that sufficient light has reached the film to provide the desired exposure. The viewfinder meter display is enabled by applying slight pressure to the shutter release (only if the shutter is not locked), the meter will then stay active for approximately 25 seconds after which it will shut down so that very little current is drawn from the batteries. The IDM exposure system provides accurate exposure readings and step-less shutter automation from as low as 125 sec to 1/2000 second and there have been LX user reports stating that the metering system has proven accurate for automated exposure duration beyond 45 minutes. The LX exposure system is extremely capable in both very low or dynamic light. Exposure metering is via a silicon photo diode (SPD) and lens assembly mounted in the floor of the mirror box and angled towards the film plane. When the reflex mirror is in the rest position (ie. the viewfinder is not blanked) the some of the incoming light passes through a semi-silvered area in the centre of the reflex mirror and is reflected into the SPD by a small secondary mirror behind the main reflex mirror. The amount of light falling on the SPD, the shutter speed dial, the ISO selector/exposure compensation dial and aperture indication are simultaneously analysed by a fast exposure computer which in turn indicates a suitable shutter speed. Exposure compensation is generally easy to guess as the IDM exposure system has a predictable centre weighted average response (biased slightly towards the base of the finder frame). Another significant advantage of the IDM system is that automatic exposure measurements remain unaffected by any light transmission differences between the various focusing screens or by changing viewfinders or by stray light entering the viewfinder. When used with the Pentax "T" flash units or compatible dedicated flash units the Pentax LX IDM exposure system allows automated TTL flash exposure operation for combinations of natural light, flash and multiple flash. Synchronisation is automatically enabled as soon as the flash is fully charged and some Pentax flash models (AF-280T and AF-400T) provide an auto exposure check in the viewfinder (using a flash test button on the flash rear) plus flash exposure confirmation in the viewfinder. The Pentax IDM system offers other interesting and useful capabilities, since the exposing light falling on the film plane is integrated to provide the correct exposure the light that is present during the exposure need not be constant. The light may be "painted" over the subject via a torch or may consist of multiple short duration flashes form various angles depending upon the ambient light and film etc. In situations where the mirror system needs to be locked up the IDM system can provide limited visual metering (full aperture only and the shutter mechanism must be advanced) however it will provide fully automated exposures with the mirror locked up at any aperture. When dry shooting the LX (without film loaded) there will be a significant difference between the meter indication and the actual shutter speed during exposure since the reflectivity of the bare pressure plate is significantly less than an average film emulsion so the IDM system appropriately compensates for the deficit by extending the exposure period. Exposure System Limitations: There is no provision for exposure lock on the Pentax LX therefor when using auto exposure mode the compensation dial is the only means by which to modify exposures. The exposure compensation dial lock is not well conceived since for many LX owners applying compensation is a two handed operation due to the position of the lock button. When using a polarizing filter on a lens fitted to the LX the photographer should note that a linear polarizing filter can lead to erroneous pre-exposure meter results, this inconsistency is caused by the summation of the polarizing effect of the secondary reflex mirror and the linearly polarized light passed by the filter. Auto exposure will not be affected by the use of a linear polarizer however if the camera is to metering is to be relied upon for manual exposures a circular polarizing filter should be used. When using a flash unit with Pentax TTL dedication activated the flash operation will only be allowed at 1/60 second or less as determined by the IDM exposure system for the given aperture and ambient lighting, full flash exposure is only possible at a shutter speed greater than 1/60 second excepting when the mode is set to manually to the X position (1/75 second flash synchronisation). Even though the Pentax LX has an exceptional exposure system sensitivity (EV -6.5 to +20 @ 100ISO using f1.2 lens) is surprisingly not so well suited to use with the new generation of ultra-fast films. No over exposure compensation is available for films rated at 3200ISO and only one stop of over exposure compensation is available for 1600ISO films (for the 3200ISO LX variant, the 1600ISO variant is one stop slower). Accessories: Finder System: Pentax LX system supports a comprehensive set of interchangeable viewfinders and focusing screens, which are generally more compact and featured than current offerings from other manufacturers. All optical surfaces in the viewfinders have been treated with the exclusive Pentax SMC coating process providing optimum contrast and visibility. There are a total of eight interchangeable viewfinders, covering eye level finders, waist level, high magnification above-camera finder and a four-part multi-function system finder. The system finder group consists of a base prism unit with a small bayonet flange and lock button and three eyepieces. The finders couple with the base to provide 45 degree finder, 45 degree high magnification finder and the sports finder provides; high eye point position, extended eye relief combined with 180 degrees rotation in order to enable above camera or eye level viewing. All of the finders maintain the viewfinder display functions such as shutter speeds, flash ready signal/exposure warning and exposure compensation flag plus all the finders display a 98% horizontal and 95% vertical view of the actual frame. The FA-1 and FA-1W eye level finders and the FB-1 System Finder base coupled with the FC-1 Action Eyepiece also allow the lens aperture ring setting to be viewed through the viewfinder. The FE-1 Magni-Finder and FF-1 Waist-Level finders each present the finder image and viewfinder information flipped left to right. The FA-1, FA-1W and FA-2 eye level finders have built-in dioper correction which is continuously variable and is easily set via a screw at the base of the finder. The LX FA series finders can be coupled with a variety of slip-on accessories such as the Magnifier-M, Refconvertor-M, Eye Cup-M, Correction Lens Adapter-M and a series of SMC Correction Lens Adapter-M in the range of +3 to -5 diopters. Finder models and details:
Index
Focusing Screens:
2000 Focusing Screens:
The Pentax LX Interchangeable Focusing Screens are very susceptible to damage, the Fresnel lens and finder surface can even be damaged by the slightest finger pressure or any attempt to remove skin oils or any other foreign matter, damage to the screen is usually obvious and distracting so extreme caution should be taken during screen changes. The Focusing Screens are supplied in a neat protective flip-top case which also houses a special spring loaded pincer designed to securely hold the screen (via a small protruding tab on the edge of the screen) plus it has a flat tool at one end shaped to aide in the release and replacement of the screen retainer frame. The screen case also provides a small slot designed to stand the replaced screen during the exchange so as to prevent damage. Check this link for More on Pentax LX Focusing Screens. Any LX finders can be used in conjunction with any one of the 12 user interchangeable focusing screens in order to provide optimal viewing conditions for any situation. MX screens will also readily fit the LX however due advances in screen design the finder image will appear less bright. There are also some special purposes third party screens produced to fit the LX, some manufacturers claim that their screens can provide a brighter image than the original Pentax screens.
Motor Drive LX System and Winder LX:
The Motor Drive LX and Winder LX for the Pentax LX both mount on the base of the LX camera body via a single thumb-screw in the tripod socket, electrical and mechanical interconnection of the body to the drives is automatic.
The covers on the camera transport access ports need to be manually removed for either drive to be added, the covers are not convenient but they do ensure that the Pentax LX has better than average protection against moisture and dust ingress. Warnings are provided in the manuals stating that loaded film may be damaged if the access ports are exposed to bright light whilst the covers are removed and a drive unit is not fitted, it is also advisable to ensure that the units are switched to the off position whilst adding or removing any components.
The Motor Drive and Winder film advance systems differ as follows;
The Motor Drive provides a higher maximum frame rate of 5 frames per second, the rate is continuously variable to 0.5 frames per second and it has a port for power and remote operation. The Motor Drive battery pack options are separate from the Motor Drive unit, there is a rechargeable Ni-Cd Battery Pack M which mounts along the base of the Motor Drive or the replaceable cell Battery Grip M which is a tall vertical grip.
The Ni-Cd Battery Pack M has an auxiliary shutter release button positioned for ease of use whilst the camera is in portrait orientation and the Battery Grip M has a trigger style shutter release button, both battery packs can be used as a remote release when attached to the Motor Drive via the 3m or 10m Power Cord M.
The Winder allows up to two frames per second continuous or single shot, the power source is integrated in the base of the Winder and consists of four standard AA cells, there is a port for a Pentax Remote Control Cord.
Both units provide a film rewind function that is manually actuated plus secondary tripod sockets in their bases. There is also bulk film option, mains powered Motor Drive power unit with integrated period timer and a variety of interconnect cable options.
It should be noted that when the camera body, Motor Drive and rechargeable battery pack is stacked on a tripod with lenses heavier than about 500 grams there is a considerable degree of undesirable vertical flexure in the assembly, also no automatic film advance functions can be used successfully using any auto-film advance component in conjunction with the built-in self timer.
Data Backs:
The Pentax LX system has two accessory data backs, the Dial Data LX and Data LX, these backs allow data to be included on the exposure in a variety of means including hand written notes. The standard LX back and data backs can be easily exchanged since each has a sprung quick release pin on the hinge does not require special tools to operate.
Grips:
There are two auxiliary grips available for the Pentax LX system which greatly enhance grip and comfort, Grip-B is a shapely pre-moulded grip (65mm x 24mm x 20mm HxWxD) which clips neatly onto the left hand accessory lug and is affixed via a small screw with to the threaded lug below the accessory grip lug.
The LX Grip A comes supplied as a large block (80mm x 25mm x 22mm HxWxD) with a circular cut-out to accommodate the swing of the multi-function lever, it is fabricated of chocolate coloured plastic. The Grip-A is designed to be shaped by the user to suite themselves, the plastic material can be readily whittled with a sharp blade and sanded in order to achieve the desired contours. It attaches to the body similarly to the Grip-B but it extends about 15mm further downward than the Grip-B making it more suitable to be customised for use with the Motor Drive LX or Winder LX.
Miscellany:
In extremely cold weather applications the LX battery may become unreliable as the minimum operating temperature for the battery may be exceeded, to overcome this problem the Pentax Battery Cord LX/A will allow the camera battery to be kept warm under the photographers clothing.
Production Variants:
The Pentax LX body has remained virtually unchanged throughout its production life discounting the special edition limited production Pentax LX versions, however as expected there were many minor design revisions (300 unconfirmed).
The obvious variations include; a re-designed shutter release lock, the addition of a film roller next to the pressure plate, an extension of the flange around ISO selector lock button, an ISO selector range extension to 3200ISO, a revised shutter curtain (indicated by the omission of two dots from the regular reflective dot pattern array on the first shutter curtain) and a modification which causes the prism release lock button to activate the light metering (this modification makes assessing exposures whilst using a Motor Drive LX or Winder LX far more convenient).
Common Faults:
"Sticky Mirror", this problem seems to occur in older LX bodies, and is indicated by a prolonged or incomplete mirror/shutter cycle the first time the shutter is tripped after the camera has been idle for weeks, days, or in some cases as little as a few hours.
Also the mirror rest may become compressed, if this occurs the mirror will be supported at a lower position which in turn slightly affects the finder view. This effect results in the actual plane of focus on the film lying behind the subject in focus as viewed through the viewfinder. For more detailed information check the page Pentax LX Problems.
Other Age Effects:
The reflex mirror may become contaminated by sticky black greasy material deposits from a deteriorating expanded foam gasket at the top of the mirror box.
Intermittent or erratic meter reading and/or unpredictable shutter timing may be resolved by rotating the ISO/exposure compensation dial but if not the assembly contacts may have been irreparably damaged by moisture, wear or the miniature ceramic circuit board may have developed an intermittent hair-line crack, the only solution then is repair.
On well used bodies the leatherette tends to eventually harden, curl and peel away from the body panels in the areas where they are subject to grease from fingers, cheeks and noses etc. however the leatherette is easily replaced.
An authorised Pentax repair centre should be able to resolve any of the problems mentioned above until the stocks of parts are exhausted.
Conclusion:
In conclusion the Pentax LX endures as a great tool for the exploration and realisation of many unique creative ideas, though dated by current standards it remains a most capable and enjoyable photographic instrument.
Other Pentax LX Web Resources:
The text contained in this document represents my opinions only, and as such I will not be held liable for detrimental consequences that arise from the application of any information within or relating to this document. All references to trade marks and or trade names are acknowledged as belonging to their respective owners.
Thanks to the many participants of the Pentax Discuss Mail List and particularly Roger Stockton for the continuous flow of valuable information, constructive criticism and assistance. This document is continuously being reviewed and refined, please let me know of any errors found in this text. Technical information was obtained from many Pentax manuals and marketing publications.
This complete document may be copied, re-posted, linked-to or used within other publications providing that permission from the author is sought and granted and that there exists a visible reference to Rob Studdert as author in any referring text. I am not a camera technician nor do I represent Pentax or their affiliates.
Rob Studdert
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