M42 lens mount
Encyclopedia
The M42 lens mount
is a screw thread
mounting standard for attaching lenses to 35 mm
cameras, primarily single-lens reflex
models. It is more accurately known as the M42 × 1 mm standard, which means that it is a metric
screw thread of 42 mm diameter
and 1 mm thread pitch. It was first used in Zeiss' Contax
S of 1949; this East German branch of Zeiss also sold cameras under the Pentacon
name; after merger with other East German photographic manufacturers, the name Praktica
was used. M42 thread mount cameras first became well-known in Japan
under the Praktica brand, and thus the M42 mount is known as the Praktica thread mount there. Since there were no proprietary elements to the M42 mount, many other manufacturers used it; this has led to it being called the Universal thread mount or Universal screw mount by many. The M42 mount was popularized in the United States
by Pentax
; thus, it is also known as the Pentax thread mount, despite the fact that Pentax did not originate it.
The Tamron T2 mount
also uses a 42mm thread, but the pitch is finer at 0.75 mm, and the T-mount is further from the film plane
. The two lens mounts are not interchangeable, and attempting to mount an M42 lens on a T2 mount — and vice-versa — will damage the thread of both the lens and the mount.
The first lenses were plain stop-down design but many manufacturers extended the M42 lens mount to provide extra features. The first innovation was the pre-select type, which allowed an aperture value to be pre-selected without actually closing the aperture, with a separate ring to close down the aperture quickly to the chosen value. This gave the user the benefit of comfortable framing and focusing with a bright viewfinder and clear focus separation, and then closing the aperture without the need to remove the eye from the eyepiece. A further development followed with "auto" lenses, which have a pin in the mount which closes the aperture against a spring to the chosen setting when it is pushed. This was adopted as a common standard by virtually all lens manufacturers. Cameras designed for these lenses have a bar in the bottom of the mount which depresses the pin when the shutter is released. The first cameras, such as the Praktica Nova range, used physical finger pressure on the shutter button to operate the bar and close the aperture, allowing a stopped-down preview of the depth of field before the shutter fired. However, this function was removed in later Praktica models because some users found it was possible, with longer exposure times, to release the shutter button and open the aperture before the shutter had closed. The bar on Pentax Spotmatic
cameras is operated by spring pressure with timing linked to the shutter, but these cameras also had a separate switch for the light meter circuit which closed the aperture and gave the depth of field preview in this way. To allow auto lenses to be used on earlier cameras without the bar, many lenses were provided with a switch or button to put the lens into stop-down mode, commonly referred to as the Auto-Manual or A/M switch.
The last development of M42 lenses was the introduction of a link between camera and lens to transmit the lens aperture setting, which allowed light metering with the aperture remaining wide open. The means of doing this was not standardised, Praktica's method was to use an electrical connection which transmitted a variable resistance value to the camera's metering circuit. Asahi Pentax developed an additional lever on the lens which operated a variable resistor in the camera mount. These mechanisms spurred the use of electronic shutters linked to the metering circuit, allowing for automated shutter speed selection by the camera (aperture priority
). M42 cameras with wide open metering facility include:
or automated selection of aperture (shutter priority
) for
Forward and backward compatibility was maintained so that the newer lenses could be used on older cameras, and old standard lenses could be used on the newer cameras, but of course without the advanced automation.
Chinon
used a different system to provide aperture priority mode with standard Auto-M420097 lenses with the CE Memotron (1974), CE-II Memotron and CE-3 Memotron bodies. A similar system was used in the Cosina
Hi-Lite EC. These cameras retained the facitlty of closing the aperture with finger pressure on the release button so that the image could be framed and focussed normally with the lens wide open. As the shutter button was depressed the lens would firstly be stopped down to the selected aperture, then the meter would be switched on and a reading taken. Chinon used a then-modern Silicon (Si) metering cell with fast reaction time compared to the then-standard CdS cells, which made it possible to close the aperture, meter the light and set the shutter speed automatically in one full press of the button. While this method did not offer the same sensitivity advantage of true open-aperture metering, it was much more versatile as it did not require specially-equipped proprietary lenses. Both Cosina and Chinon sold their cameras to various other companies for rebranding
, which increased the number of almost identical cameras considerably.
Compatibility problems have been experienced when mounting lenses with aperture transmission levers (e.g., SMC Takumars) on older bodies such as Zenit-E or Mamiya DTL. The aperture lug or a pin can interlock with the screwheads affixing the mount, which then impedes lens removal.
M42 mount cameras fell out of general production during the late 1970s and early 1980s, with the exception of the Russian Zenit
range. Pentax moved to the Pentax K mount
from 1975 onwards, whilst Praktica adopted the electronic B-Mount in 1979. It was briefly revived with the Cosina
-made Voigtländer Bessaflex TM launched in 2003 but this was discontinued in 2007. M42 lenses are still in production at KMZ and at Cosina (under the Voigtländer brand and the ZS line for Carl Zeiss).
line of SLRs from the USSR and Russia (some models)
Praktica
SLRs from East Germany (not the B-Series)
Pentax
SLRs from Japan (some models)
Zeiss Ikon Icarex TM and SL-706
Voigtländer Bessaflex TM (2003–2007)
less than or equal to M42's flange depth, which includes the popular Canon EF
-mount, the Pentax K-mount, the Minolta/Konica Minolta/Sony A-mount
, the Sony E-mount and the Four Thirds System
including the Micro Four Thirds system. This allows the lens to be mounted the correct distance from the film or sensor, retaining the original focus range of the lens.
For some M42 lenses, the rear element extend too far into the camera body, causing clashes with the mirror mechanism, sometimes breaking it. This problem is known to occur with Takumar lenses and Canon bodies. Sony bodies are immune to this problem.
On bodies with a flange focal distance
greater than that of M42, most notably Nikon, three options are available. A simple mechanical adaptor allows the lens to be mounted, but the effect is similar to the introduction of an extension tube, reducing the minimum focus distance at the expense of losing infinity focus. Alternatively, an adaptor with an optical element can be used to retain the original focus range of the lens, at the expense of some image quality. Finally, it is possible to replace the M42-mount on some lenses with a Nikon F-mount, or to perform the reverse change on a Nikon camera body. The latter process will, of course, render the camera unable to use the F-mount lenses it was originally designed for.
The level of functionality available from a modern body when an M42 lens is mounted may vary. Some bodies may be operated in aperture-priority mode, others will only allow full manual control in this circumstance. Focus confirmation may not be available. Mounting an M42 lens on a digital SLR with a sensor smaller than 35 mm film results in FOV crop
.
Lens mount
A lens mount is an interface — mechanical and often also electrical — between a photographic camera body and a lens. It is confined to cameras where the body allows interchangeable lenses, most usually the single lens reflex type or any movie camera of 16 mm or higher gauge...
is a screw thread
Screw thread
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...
mounting standard for attaching lenses to 35 mm
135 film
The term 135 was introduced by Kodak in 1934 as a designation for cartridge film wide, specifically for still photography. It quickly grew in popularity, surpassing 120 film by the late 1960s to become the most popular photographic film format...
cameras, primarily single-lens reflex
Single-lens reflex camera
A single-lens reflex camera is a camera that typically uses a semi-automatic moving mirror system that permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to pre-SLR cameras where the view through the viewfinder could be significantly...
models. It is more accurately known as the M42 × 1 mm standard, which means that it is a metric
Metric system
The metric system is an international decimalised system of measurement. France was first to adopt a metric system, in 1799, and a metric system is now the official system of measurement, used in almost every country in the world...
screw thread of 42 mm diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
and 1 mm thread pitch. It was first used in Zeiss' Contax
Contax
Contax was a camera brand noted for its unique technical innovation and a wide range of Zeiss lenses, noted for their high optical quality. Its final incarnation was a line of 35 mm, medium format and digital cameras engineered and manufactured by Kyocera, and featuring modern Zeiss optics...
S of 1949; this East German branch of Zeiss also sold cameras under the Pentacon
Pentacon
Pentacon is the company name of a once-important camera manufacturer in Dresden, Germany.The name Pentacon is derived from the brand Contax of Zeiss Ikon Kamerawerke in Dresden and Pentagon, as a Pentaprism for Single-Lens Reflex cameras was for the first time developed in Dresden...
name; after merger with other East German photographic manufacturers, the name Praktica
Praktica
Praktica is a brand of camera manufactured by Pentacon in Dresden in eastern Germany, formerly within the GDR prior to reunification. Pentacon is the modern-day successor to Dresden camera firms such as Zeiss Ikon, and for many years Dresden was the world's largest producer of cameras...
was used. M42 thread mount cameras first became well-known in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
under the Praktica brand, and thus the M42 mount is known as the Praktica thread mount there. Since there were no proprietary elements to the M42 mount, many other manufacturers used it; this has led to it being called the Universal thread mount or Universal screw mount by many. The M42 mount was popularized in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
by Pentax
Pentax
Pentax is a brand name used by Hoya Corporation for its medical-related products & services and Pentax Ricoh Imaging Company for cameras, sport optics , etc. Hoya purchased and merged with the Japanese optics company on March 31, 2008. Hoya's Pentax imaging business was sold to Ricoh Company, Ltd...
; thus, it is also known as the Pentax thread mount, despite the fact that Pentax did not originate it.
The Tamron T2 mount
T-mount
T-mount is a standard lens mount for cameras and other optical assemblies.The T2 version is a screw mount using a male M42x0.75 metric thread on the lens with a flange focal distance of 55 mm, and a mating female thread on a camera adapter or other optical component. This thread form is referred...
also uses a 42mm thread, but the pitch is finer at 0.75 mm, and the T-mount is further from the film plane
Film plane
A film plane is the area inside any image taking device with a lens and a digital sensor or film; such as a camera. The film plane varies in distance from the lens focal point in each manufacturer...
. The two lens mounts are not interchangeable, and attempting to mount an M42 lens on a T2 mount — and vice-versa — will damage the thread of both the lens and the mount.
Evolution and automation
The M42 mount was first developed by Carl Zeiss at their Jena plant in 1938 at the request of the KW camera company for their Praktica line, which had previously used M40 (40 mm by 1 mm DIN).The first lenses were plain stop-down design but many manufacturers extended the M42 lens mount to provide extra features. The first innovation was the pre-select type, which allowed an aperture value to be pre-selected without actually closing the aperture, with a separate ring to close down the aperture quickly to the chosen value. This gave the user the benefit of comfortable framing and focusing with a bright viewfinder and clear focus separation, and then closing the aperture without the need to remove the eye from the eyepiece. A further development followed with "auto" lenses, which have a pin in the mount which closes the aperture against a spring to the chosen setting when it is pushed. This was adopted as a common standard by virtually all lens manufacturers. Cameras designed for these lenses have a bar in the bottom of the mount which depresses the pin when the shutter is released. The first cameras, such as the Praktica Nova range, used physical finger pressure on the shutter button to operate the bar and close the aperture, allowing a stopped-down preview of the depth of field before the shutter fired. However, this function was removed in later Praktica models because some users found it was possible, with longer exposure times, to release the shutter button and open the aperture before the shutter had closed. The bar on Pentax Spotmatic
Pentax Spotmatic
The Pentax Spotmatic is a range of 35mm single-lens reflex cameras manufactured by the Asahi Optical Co. Ltd., later known as Pentax Corporation, between 1964 and 1976. The original 1964 Spotmatic was one of the first SLRs to offer a through-the-lens exposure metering system, initially using...
cameras is operated by spring pressure with timing linked to the shutter, but these cameras also had a separate switch for the light meter circuit which closed the aperture and gave the depth of field preview in this way. To allow auto lenses to be used on earlier cameras without the bar, many lenses were provided with a switch or button to put the lens into stop-down mode, commonly referred to as the Auto-Manual or A/M switch.
The last development of M42 lenses was the introduction of a link between camera and lens to transmit the lens aperture setting, which allowed light metering with the aperture remaining wide open. The means of doing this was not standardised, Praktica's method was to use an electrical connection which transmitted a variable resistance value to the camera's metering circuit. Asahi Pentax developed an additional lever on the lens which operated a variable resistor in the camera mount. These mechanisms spurred the use of electronic shutters linked to the metering circuit, allowing for automated shutter speed selection by the camera (aperture priority
Aperture priority
Aperture priority, often abbreviated A or Av on a camera mode dial, is a setting on some cameras that allows the user to choose a specific aperture value while the camera selects a shutter speed to match. The camera will ensure proper exposure...
). M42 cameras with wide open metering facility include:
- Praktica PLC2, EE 2 and EE 3 (1975, 1977, 1979) (EE = Electric Eye)
- Fujica ST901
- Olympus FTLOlympus FTLThe Olympus FTL was a 35mm SLR sold by Olympus between 1971 and 1972. It was a transition model between the Pen F half-frame SLR and full-frame M-1.The FTL was a very traditional SLR with 42mm screw lenses.-Accessories:...
(1970) - Pentax Spotmatic F, Electro Spotmatic (Japan only), ES and ESII (1975, 1971-3)
- Yashica Electro AX (1972)
or automated selection of aperture (shutter priority
Shutter priority
Shutter priority refers to a setting on some cameras that allows the user to choose a specific shutter speed while the camera adjusts the aperture to ensure correct exposure...
) for
- Ricoh TLS-EE (1973)
- Petri-designed Exakta FE 2000 (1978)
Forward and backward compatibility was maintained so that the newer lenses could be used on older cameras, and old standard lenses could be used on the newer cameras, but of course without the advanced automation.
Chinon
Chinon Industries
was a Japanese camera manufacturer. Kodak took a majority stake in the company in 1997, and made it a fully owned subsidiary of Kodak Japan, , in 2004 . As a subsidiary, it continues to develop digital camera models....
used a different system to provide aperture priority mode with standard Auto-M420097 lenses with the CE Memotron (1974), CE-II Memotron and CE-3 Memotron bodies. A similar system was used in the Cosina
Cosina
is a designer and manufacturer of cameras and lenses, and a glassmaker, based in Nakano, Nagano Prefecture, Japan.-History:Cosina is the successor to Nikō , a company set up as a manufacturer oflenses in 1959...
Hi-Lite EC. These cameras retained the facitlty of closing the aperture with finger pressure on the release button so that the image could be framed and focussed normally with the lens wide open. As the shutter button was depressed the lens would firstly be stopped down to the selected aperture, then the meter would be switched on and a reading taken. Chinon used a then-modern Silicon (Si) metering cell with fast reaction time compared to the then-standard CdS cells, which made it possible to close the aperture, meter the light and set the shutter speed automatically in one full press of the button. While this method did not offer the same sensitivity advantage of true open-aperture metering, it was much more versatile as it did not require specially-equipped proprietary lenses. Both Cosina and Chinon sold their cameras to various other companies for rebranding
Rebranding
Rebranding is the creation of a new name, term, symbol, design, or a combination of them for an established brand with the intention of developing a differentiated position in the mind of stakeholders and competitors....
, which increased the number of almost identical cameras considerably.
Compatibility problems have been experienced when mounting lenses with aperture transmission levers (e.g., SMC Takumars) on older bodies such as Zenit-E or Mamiya DTL. The aperture lug or a pin can interlock with the screwheads affixing the mount, which then impedes lens removal.
M42 mount cameras fell out of general production during the late 1970s and early 1980s, with the exception of the Russian Zenit
Zenit (camera)
Zenit is a Russian camera brand manufactured by KMZ in the town of Krasnogorsk near Moscow since 1952 and by BelOMO in Belarus since the 1970s. The Zenit trademark is associated with 35mm SLR cameras...
range. Pentax moved to the Pentax K mount
Pentax K mount
The Pentax K mount, sometimes referred to as the "PK mount", is a lens mount standard for mounting interchangeable photographic lenses to 35 mm single-lens reflex cameras. It was created by Pentax in 1975, and has been used by all Pentax 35 mm and digital SLRs since...
from 1975 onwards, whilst Praktica adopted the electronic B-Mount in 1979. It was briefly revived with the Cosina
Cosina
is a designer and manufacturer of cameras and lenses, and a glassmaker, based in Nakano, Nagano Prefecture, Japan.-History:Cosina is the successor to Nikō , a company set up as a manufacturer oflenses in 1959...
-made Voigtländer Bessaflex TM launched in 2003 but this was discontinued in 2007. M42 lenses are still in production at KMZ and at Cosina (under the Voigtländer brand and the ZS line for Carl Zeiss).
Notable Cameras Produced for the M42 Mount
ZenitZenit (camera)
Zenit is a Russian camera brand manufactured by KMZ in the town of Krasnogorsk near Moscow since 1952 and by BelOMO in Belarus since the 1970s. The Zenit trademark is associated with 35mm SLR cameras...
line of SLRs from the USSR and Russia (some models)
Praktica
Praktica
Praktica is a brand of camera manufactured by Pentacon in Dresden in eastern Germany, formerly within the GDR prior to reunification. Pentacon is the modern-day successor to Dresden camera firms such as Zeiss Ikon, and for many years Dresden was the world's largest producer of cameras...
SLRs from East Germany (not the B-Series)
Pentax
Pentax
Pentax is a brand name used by Hoya Corporation for its medical-related products & services and Pentax Ricoh Imaging Company for cameras, sport optics , etc. Hoya purchased and merged with the Japanese optics company on March 31, 2008. Hoya's Pentax imaging business was sold to Ricoh Company, Ltd...
SLRs from Japan (some models)
Zeiss Ikon Icarex TM and SL-706
Voigtländer Bessaflex TM (2003–2007)
Use on modern cameras
Because of the simplicity of the M42 lens mount and the large selection of existing lenses, M42 adaptors exist for all current and many obsolete lens mounts. This adapter fits between the camera and the lens, making it possible to mount a M42 lens on a body with a different mount. This allows the use of M42 lenses on modern film and digital SLRs. M42 adaptors work best on bodies with a flange depthFlange focal distance
For an interchangeable lens camera, the flange focal distance of a lens mount system is the distance from the mounting flange to the...
less than or equal to M42's flange depth, which includes the popular Canon EF
Canon EOS
The Canon EOS autofocus 35 mm film and digital SLR camera system was introduced in 1987 with the Canon EOS 650 and is still in production as Canon's current DSLR system...
-mount, the Pentax K-mount, the Minolta/Konica Minolta/Sony A-mount
Minolta AF
The Minolta Alpha camera system was a collection of photographic equipment from Minolta. The system used a lens mount called A-mount, with a flange focal distance 44.50 mm. The new mount was larger than the older SR-mount making old manual lenses incompatible with the new system...
, the Sony E-mount and the Four Thirds System
Four Thirds System
The Four Thirds system is a standard created by Olympus and Kodak for digital single-lens reflex camera design and development.The system provides a standard that, with digital cameras and lenses available from multiple manufacturers, allows for the interchange of lenses and bodies from different...
including the Micro Four Thirds system. This allows the lens to be mounted the correct distance from the film or sensor, retaining the original focus range of the lens.
For some M42 lenses, the rear element extend too far into the camera body, causing clashes with the mirror mechanism, sometimes breaking it. This problem is known to occur with Takumar lenses and Canon bodies. Sony bodies are immune to this problem.
On bodies with a flange focal distance
Flange focal distance
For an interchangeable lens camera, the flange focal distance of a lens mount system is the distance from the mounting flange to the...
greater than that of M42, most notably Nikon, three options are available. A simple mechanical adaptor allows the lens to be mounted, but the effect is similar to the introduction of an extension tube, reducing the minimum focus distance at the expense of losing infinity focus. Alternatively, an adaptor with an optical element can be used to retain the original focus range of the lens, at the expense of some image quality. Finally, it is possible to replace the M42-mount on some lenses with a Nikon F-mount, or to perform the reverse change on a Nikon camera body. The latter process will, of course, render the camera unable to use the F-mount lenses it was originally designed for.
The level of functionality available from a modern body when an M42 lens is mounted may vary. Some bodies may be operated in aperture-priority mode, others will only allow full manual control in this circumstance. Focus confirmation may not be available. Mounting an M42 lens on a digital SLR with a sensor smaller than 35 mm film results in FOV crop
Crop factor
In digital photography, a crop factor is related to the ratio of the dimensions of a camera's imaging area compared to a reference format; most often, this term is applied to digital cameras, relative to 35 mm film format as a reference. In the case of digital cameras, the imaging device would be a...
.
Compatibility
Pentax: All DSLRs allow aperture-priority with focus confirmation and infinity focus. With certain adapters or simply grounding one contact with foil, focus-trap is available.Specifications
- Thread: M42 × 1
- Flange focal distanceFlange focal distanceFor an interchangeable lens camera, the flange focal distance of a lens mount system is the distance from the mounting flange to the...
: 45.5 mm (The figure 45.46 mm is also commonly seen, particularly in Pentax literature)