Takumar

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Takumar refers to a line of high quality photographic lenses produced by Asahi Optical Co beginning in the 1950s. The name is a reference to Takuma Kajiwara (Kajiwara Takuma)[1], a well known Japanese-American photographer and painter, who was the younger brother of Kumao Kajiwara founder of Asahi Kogaku Kogyo G.K. (Asahi Optical Corp). The analogy of using of lenses to paint with light as if they were brushes and the addition of the letter R to the end gave the name Takumar a nice poetic ring.

The name Takumar was used in lenses for Asahi Pentax 35mm, in M37 amd M42 mounts, becoming very famous with the popularity of the Spotmatic lines of cameras. The name was also used for lenses for the 6x7 SLR (Pentax 67). Takumar was the name of Pentax lenses until 1976, when K-mount replaced M42 and Pentax replaced Asahi, from then on lenses were badged mostly SMC Pentax, even though a few still had the name Takumar. Late in the 1980s Takumar was used for budget lenses for Pentax-K mount. Several million lenses using this name were made which are widely available and have been adapted to many digital camera systems.

Takumars were also used in cameras of other makers, notably in the Suzuki Press Van cameras with the Asahi Kogaku Takumar 75mm f/3.5

Asahi Optical is one of the oldest lens manufacturers in Japan, with complete capabilities of design, melting, and polishing several types of glass and mechanical engineers for the focusing mechanism, as such they made lenses for their own cameras, as well as some other companies. The first appearance of the name Takumar was in lenses used in the Asahiflex camera, which used the 37mm screw mount (1952). Takumar was carried over to lenses that fit the 35mm M42(1957-1973) cameras and went through a series of iterations as build quality and coatings were developed with names such as Super-Takumar, Super-Multi-Coated Takumar, and SMC Takumar (with open-metering capability). These lenses were made at a high standard of optical and mechanical quality and all lenses were provided in a leather case and a custom lens hood, except those that came as standard lenses with camera bodies. Filter sizes were also standardized by Asahi in order to help customers, being 49mm and 58mm for most 35mm lenses.[2][3][4]

In 1969 Asahi introduced the Pentax 6x7 camera, an oversized SLR capable of using 120 and 220 film and a line of Super Takumar 6x7 lenses was created for it. In 1971 these were upgraded to SMC Takumar 6x7 until the name was changed to SMC Pentax in the late 1970s.

These lenses are highly regarded among photographers, with some achieving cult-like status such as the Takumar 50mm f/1.4, 135mm f/2.5 and 35mm f/2.0. The build and optical quality are superb and the easiness to adapt M42 mount to new camera mounts has transcended the use in new digital SLRs and mirrorless cameras.

Asahiflex Lenses

The Asahiflex was a unique camera with a 37x1 mm screw lens mount, for this camera Asahi launched a whole line of lenses badged Asahi Kogaku Takumar.[5] All these lenses were made in chrome finished brass, with a few black trimmings in some late examples. [6]

These Takumars have some other interesting quirks. The aperture is pre-set and the iris is made up of 20 blades giving a nice round lens opening. [5] [6]

No wide angle lenses were made at this point, which was a common problem for SLR makers of the time,until retro-focus was discovered by Angenieux in the late 50s.

It's also of note that Asahi kept producing lenses for the Asahiflex after moving to M42 mount, retrofitting M42 lenses for the M37 mount as marked in the list.[2]

  • Standard lenses:
    • Takumar 50mm f/3.5 (3 different versions)
    • Takumar 58mm f/2.4
  • Telephotos:
    • Takumar 83mm f/1.9 (both in Asahiflex and M42 with adapter mount)[7]
    • Takumar 100mm f/3.5
    • Tele-Takumar 135mm f/3.5
    • Takumar 135mm f/3.5 (M42 with adapter)
    • Takumar 500mm f/5.0

M42 Lenses


Asahi adopted the M42x1mm lens mount, which was originally developed by Contax, and used by Praktica, Pentacon and others, for their original Pentaprism SLR camera in 1957, the original Asahi Pentax (AP) which is known as the first modern Japanese camera. The M42 mount continued to be used in a large variety of cameras until 1975. The badge Takumar was unchanged from the M37 lenses but are easily distinguishable by the change fom Asahi-Kogaku to Asahi-Optical and the scales in meter and feet depending on the target market. Takumar lenses were preset and initially came in a combination of black and chrome brass, these are listed as type 0 in the list of lenses and were used in the Asahi Pentax AP and the Asahi Pentax S, updated line came for the Asahi Pentax K (Tower 29) cameras in 1959. Several of these lenses were sold by Sears-Roebuck & Co in the USA as complement for their TOWER brand of cameras.[2]

The limitation of wide-angle construction were solved by this time (retro focus solution by Angenieux) , and Asahi developed a 35mm f/4.0 lens which was followed by the 35mm f/3.5 that was very popular and produced with changes in M42 and K-mount up to 1979.{br}

Auto Takumar

These lenses were introduced in 1958 for use with the Pentax K camera (Tower 29), the improvement was the semi-automatic aperture system, consisting of 2 rings and are listed as type I. One ring sets the aperture and the other is a spring loaded ring that keeps the aperture fully open for focusing. When pressing the shutter halfway, the camera pushes a pin on the rear of the lens closing the iris to the set aperture and have DOF check, then fully pressing the shutter takes the picture. The lens remains closed until the shutter is cocked for the next exposure.[2][8] In this generation of lenses, the only known lens in "Zebra" finish was produced (Auto-Takumar 55mm/1.8).

Several of these lenses were sold by Sears-Roebuck & Co in the USA as complement for their TOWER brand of cameras with a 55mm f/1.9 made specifically for them.


Super-Takumar Lenses

The Super-Takumars were introduced around 1962, improvements included the use of lens coating and a fully-automatic diaphragm which not only closed the aperture to the preselected value, but after firing the shutter re-opened for focusing. A pin is pushed by a plate in the camera for metering and shooting, and a small lever to select "Auto/Manual" (A/M in early lenses) operation was added to use in cameras which don't support this feature. These lenses are generally single-coated however as Asahi developed coating technology some later examples are multi-coated.[2][9]

These series are marked Super-Takumar and are listed as type II. These lens were very popular, especially after the introduction of the Asahi Pentax Spotmatic and were sold by the millions. Due to the high quality of construction and optics of these lenses they are still being used by aficionados in digital cameras, with a cult-like status in some of them.

Many new lenses were developed in this era such as: 28mm, 24mm and finally a 20mm, two fisheye lenses 17mm and 11mm, telephotos 100mm, 150mm, 200mm , 400mm and for the first time Asahi made zoom lenses. Updates to existing lenses, the 35mm f/2.3 was replaced by the 35mm f/2.0 and later developed into a smaller version (49m filter) At this point the best standard lens of the era was introduced the 50mm f/1.4 first in 8-element configuration and later in a 7-element version (with Thorium glass).

Super Takumar lenses


Super Multi Coated (SMC) Lenses

In 1971 Asahi Optical had fully developed their 7-layer coating process, which at the time was the best available, and rebranded the lenses as Super-Multi-Coated lenses and listed as Type III below. A series of very thin layers of rare elements were added to each element of the lens to minimize reflections and increase light transmission to >99.8%. This process was developed by Optical Coating Laboratories Inc (OCLI) in the USA for aero-photography and adapted by Asahi for every day use. Some of the early lenses were marked Multi-Coated Super-Takumar, such as the 50mm f/1.4 that was shown with the Spotmatic II in the initial sales brochure.

Besides the multi-coating breaktrough, a mechanical linkage was built to allow for fully-open light metering with the advent of the Electro-Spotmatic in 1971 and the Spotmatic F by 1973.[9][2][10]

This mechanism passed information from the lens to the camera and was comprised of:

  1. Diaphragm pin to close when taking picture (common to Super-Takumars and other M42 mounts)
  2. Cam passing aperture information to camera
  3. Index point for the aperture system. Small variations in the lens final placement were possible due to the screw mount nature, and variations in construction
  4. Pin to prevent the Auto/Man lever to move and prevent metering errors



Most of the lenses retained the appearance and design of the Super Takumar equivalents, until a the late version, named SMC-Takumar listed as Type IV, when the knurled metal milled grip of the focus ring was replaced by a rubberized grip, and the aperture ring was also changed to match the design used in the K-mount lenses.

Super-Multi-Coated and SMC lenses


Several new lenses were launched in this series, among those the spectacular 15mm f/3.5 linear wide angle which included an aspherical element. This lens is rare and produces images with very little distortion or chromatic aberration. A telephoto zoom 135-600mm f/6.7 which besides a great performance with 15 elements in 12 groups, also accepted 49mm filters in the rear.


List of known M42 Lenses

  • type 0 (1957): Takumar-preset: Replaced the older 37mm version of the Takumar line for the original AP cameras
  • type I (1959): Auto-Takumar: A lever is added to allow for full aperture focusing before shooting, for the Pentax K camera
  • type II (1962): Super-Takumar: Fully-automatic diaphragm that does not needs to be cocked manually, and a Auto/Manual switch on the lens are present. Single layer of coating, however some later versions are multi coated as Asahi's coating technology was improving. These lenses were made popular with the success of the Spotmatic cameras. The famous 50mm f/1.4 was introduced at this time.
  • type III (1971): Super-Multi-Coated Takumar: A 7 layer coating was applied for these lenses, the best available at the time, with improvements in contrast and color rendition. A mechanism for open aperture metering with the Spotmatic-F/ES/ES-II is added to the lens.
  • type IV: SMC Takumar (1974): Identical optically to type III but uses a rubberized instead of the metal focusing ring, and a different diaphragm ring as a prelude to the change of mount to K-Bayonet.
Wide Angles Normal Short - Teleobjectives Teleobjectives Zoom and Special lenses
  • 15/3.5 (III, IV)
  • 17/4 Fisheye (II, III, IV)
  • 18/11 Fisheye (II)
  • 20/4.5 (II, III)
  • 24/3.5 (II, III)
  • 28/3.5 (II, III)
  • 35/2.0 (II, III)
  • 35/2.3 (I)
  • 35/3.5 (I, II, III)
  • 35/4.0 (0)


  • 50/1.4 (II, III, IV)
  • 50/1.8 (I, II, III)
  • 50/3.5 (0)
  • 50/4 Macro (II, III, IV)
  • 55/1.8 (0, I, II, III, IV)
  • 55/2 (0, I, II, III)
  • 55/2.2 (0, I)
  • 58/2 (0)
  • 58/2.4 (0)
  • 83/1.9 (0)
  • 85/1.8 (I, III)
  • 85/1.9 (II, III)
  • 100/2 (0)
  • 100/3.5 (0)
  • 100/4 Bellows (0, III)
  • 100/4 Macro (III)
  • 105/2.8 (0, I, II, III)
  • 108/2.8 Index (III)
  • 120/2.8 (III)
  • 135/2.5 5 elements/5 groups (II, III)
  • 135/2.5 6 elements/6groups (III)
  • 135/3.5 (0, I, II, III)
  • 150/4 (II, III)
  • 200/3.5 (0)
  • 200/4 (II, III)
  • 200/5.6 Tele (II)
  • 300/4 (0, II, III)
  • 300/6.3 Tele (II)
  • 400/5.6 (II, III)
  • 500/4.5 (0, II, III)
  • 500/5 (0)
  • 1000/8 (0, III)
  • 70-150/4.5 (II)
  • 85-210/4.5 (II, III, IV)
  • 45-125/4.0 (III)
  • 135-600/6.7 (III)


  • 85/3.5 Quartz Takumar (II)
  • 85/4.5 Ultra Achromatic (II)
  • 300/5.6 Ultra Achromatic (II)

List adapted from [2], [4], [9], [11], [12]

Pentax 6x7 system lenses

Asahi introduced an oversized SLR that could use 120 and 220 film in 1969 and called it Pentax 6x7. A series of lenses bearing the name Takumar 6x7 and Super-Takumar 6x7 were launched with it, providing a complete photography system. In 1971 with the advent of the Multi-Coating for all lens surfaces the name was changed to Super Multi Coated (SMC) Takumar 6x7[13]

A large number of lenses were developed and are listed below, list adapted from [14] and [13]

List of known Pentax 67 Lenses

Super-Takumar -1969 Super-Multi-Coated - 1971
  • 35mm f/4.5 Super-Takumar 6x7, Fisheye
  • 55mm f/3.5 Super-Takumar 6x7, filter 100mm
  • 75mm f/4.5 Super-Takumar 6x7, filter 82mm
  • 105mm f/2.4 Super-Takumar 6x7, filter 67mm
  • 150mm f/2.8 Super-Takumar 6x7, filter 67mm
  • 200mm f/4 Super-Takumar 6x7, filter 67mm
  • 300mm f/4 Super-Takumar 6x7, filter 82mm
  • 400mm f/4 Super-Takumar 6x7, filter 77mm
  • 600mm f/4 Takumar 6x7, filter 77mm
  • 800mm f/4 Takumar 6x7, filter 77mm
  • 35mm f/4.5 Super-Multi-Coated Takumar 6x7, Fisheye
  • 55mm f/3.5 Super-Multi-Coated Takumar 6x7, filter 100mm
  • 75mm f/4.5 Super-Multi-Coated Takumar 6x7, filter 82mm
  • 90mm f/4 Super-Multi-Coated Takumar 6x7 LS, filter 67mm, leaf shutter
  • 105mm f/2.4 Super-Multi-Coated Takumar 6x7, filter 67mm
  • 150mm f/2.8 Super-Multi-Coated Takumar 6x7, filter 67mm
  • 200mm f/4 Super-Multi-Coated Takumar 6x7, filter 67mm
  • 300mm f/4 Super-Multi-Coated Takumar 6x7, filter 82mm
  • 400mm f/4 Super-Multi-Coated Takumar 6x7, filter 77mm
  • 500mm f/5.6 Super-Multi-Coated Takumar 6x7, filter 95mm
  • 600mm f/4 Super-Multi-Coated Takumar 6x7, filter 77mm
  • 800mm f/4 Super-Multi-Coated Takumar 6x7, filter 77mm
  • 1000mm f/8 Reflex-Takumar 6x7


Takumar bayonet lenses

In the 1980s Pentax reused the name Takumar for a series of budget lenses for their SLRs, also sold as Cosmicar. The lenses used simplified optical formulas, lighter build quality and less expensive coatings. These lenses are badged Takumar Bayonet (K-mount); Takumar-A (KA) mount or Takumar F (KAF) mount.

Known lenses:

  • Takumar Bayonet 28mm f/2.8
  • Takumar-A 28mm f/2.8 (with electronic contacts for Av mode)
  • Takumar Bayonet 135mm f/2.5
  • Takumar Bayonet 135mm f/2.8
  • Takumar Bayonet zoom 80-200mm f/4.5
  • Takumar-A zoom 28-80mm f/3.5-4.5
  • Takumar-F Zoom 28-80mm f3.5-4.5 Macro
  • Takumar-A zoom 70-200mm f/4
  • Takumar-F zoom 70-210 f/4-5.6


Legacy and notes

Computer aided lens design

Mathematical formulations for the design of lenses have been used since the early 20th century. Bertele used algorithms to design the famous Ernostar, and later Sonnar in the 1920s and 30s and he had a team of engineers dedicated to apply the algorithms to calculate optimal geometry.[15] In the 1950s, computers could be used to solve mathematical problems faster then humans, and Asahi invested in this technology which made the process faster and in theory more precise, and in the early 1960s Asahi lens relied heavily on computers. By the end of that decade, computer-aided lens design had revolutionized the industry, and new designs were being launched by several companies. As of 2021 several commercial lens-design software packages are available. [16]

Computer aided design is prominently mentioned in the Asahi Pentax manuals, as well as in the Honeywell Lens Manual as a way to position Asahi Optical as a pioneer and leader in the field. Asahi Optical invested early in the technology which allowed them to make lenses that were balanced and produced nice tone rendition and were better corrected for aberrations than its predecessors.



A note on radioactive lenses

In order to maximize image quality, several rare elements were mixed in the glass making process used in photographic optics. Among those Thorium oxides were mixed to produce glass of high refractive index, Kodak pioneered this developments in the 1930s and applied them in many of their lenses, famously Ektar and Aero-Ektar lenses in the 1940s. Corning, Schott and others used Thoriated glass for elements in their lenses, until the 1980s when Lanthanum was used instead, and examples from many companies have been tested radioactive. [17]

Asahi used Thorium oxide in the production of optical glass in several Super-Takumar, Super-Multi-Coated, and even in a few SMC-Takumars between 1964 and 1973. In these lenses usually only one element of this glass was used, either in front or in the back. The drawback is that thoriated glass tends to discolor over time, to a yellow-brown color which can be reversed by the action of photons (bright light) and UV light.[18]

Notable lenses that have this kind of glass are: Super- and Super-Multi-Coated Takumar 50mm f/1.4 (7 element version), 20mm f/4.5, 35mm f/2, 55mm f/1.8, 55mm f/2 and 85mm f/1.8. Super Takumar 6x7 105mm f/2.4.

Fortunately most of the residual radiation is Alpha-type and is not dangerous and will not fog the film.[2] Studies carried out by the US Army show that glass attenuates alpha radiation and any residual will be absorbed in a surface layer of less than 100 micrometers. [19]


The Takumar 50/1.4

Asahi decided to develop a fast a normal lens to complement the launch of their Spotmatic camera. This lens competed against the Nikkor 50mm 1.4 and best German SLR lenses which at the time were the legendary Planar, Summicron and Ultron. Asahi had complete control over the glass manufacturing, and mechanical assembly of the lenses, which allowed them to explore a new design, derived from the Double Gauss design for a fast normal lens [20]. Together with computer aided design which, was new at the time, replaced manual calculations. The resulting design was a real jewel.

The Super-Takumar 50mm f/1.4 lens was launched without fanfare in 1964 with its 8 element in 6 group configuration (Product Nr. 358-35800), it's estimated that 125,000-170,000 were made. It is noticeable that in the Honeywell Lens Brochure from 10/65 this lens is featured a picture together with a Spotmatic camera, but is not described in the literature.

The initial version of the lens has a rear glass element that protruded enough to risk damaging the element or the push-pin mechanisms in the Pentax cameras previous to the Spotmatic. Soon after the SV/H3v and S1a/H1a were fitted with a crescent-shape push-pin plate and the rewind crank replaced with one with an orange R.[21][11][2]

Soon after, (1965) a new version with 7 elements in 6 groups was introduced, including the use of Thorium Oxide in the rear element glass and was patented in the US3451745A.[22] This version improved image quality in general and the introduction of better lens coatings increased the contrast (Product Nr. 37800,37801,37802). The lens is 15g lighter than the previous version, the noticeable external differences are that the rear element doesn't protrude as much, and the IR focusing mark was moved from the right to the left of the f/4 mark. [23] Over time this lens tends to show an amber discoloration of the rear element, due to the use of Thorium (see section in Radioactivity).

The same design with small changes was carried to the Super-Multi-Coated (Product Nr. 37902) but with an 8 blade diaphragm instead of 6, SMC (37908). Pentax has kept the 50/1.4 in their lineup through decades, maintaining the 7element in 6 group design with revisions and changes in each of the lens series, bayonet mount (K-lenses) which is cosmetically very similar to the SMC, in 1977 the SMC-M series made the lens more compact and about 30g lighter, in 1983 A-series added electronic aperture control and this was carried to the autofocus F, and FA series.

  • 1964 Asahi Super Takumar (single coated, 6 blades, sole 8/6-design)
  • 1965 Asahi Super Takumar (single coated, 6 blades, 7/6 design, Thorium element)
  • 1971 Asahi Super-Multi-Coated Takumar (Multi coated, 8 blades)
  • 1972 Asahi SMC Takumar (rubber focus ring)
  • 1975 Asahi SMC Pentax "K"
  • 1977 Asahi SMC Pentax-M (Revised formula and design)
  • 1983 SMC Pentax-A (Electronic Aperture control)
  • 1987 SMC Pentax-F (Auto focus)
  • 1991 SMC Pentax-FA

Production of the FA 50mm f/1.4 started in 1991 and the lens is still for sale in 2021[24]. Pentax launched a completely new lens in 2018 called HD PENTAX-D FA★ 1.4/50 SDM AW (15 elements, 9 groups) [25] this lens has a 9 rounded blade diaphragm, and is corected for DSLR use.

This lens has become legendary due to the image quality, and the unique look it can achieve. The older versions with the lack of multi-coating tend to produce less sharp but dreamy images, with a very eye pleasing out of focus area. In this age of Digital and movie making, it has seen a new life by the ability to be adapted to almost any mount and its relative abundance, providing even to this day an very high cost-benefit. The first 8-element version is the one more sought after due to the intangible image quality they achieve.


Using Takumar lenses on digital cameras?

Use in Pentax DSLRs:

Pentax has kept compatibility in their system for decades. When K-mount was launched (1976), and because the flange to film distance was the same, an adapter was also provided to use the M42 lenses in the "new cameras". This compatibility philosophy has continued to the digital era, and most lenses can be used in the current line of DSLR's. The M42 to K adapter is still in the inventory in 2021. [26][27]


  • Manual Focus
    • Focus confirmation provided by SAFOX autofocus
    • No focal length information on EXIF
  • Image stabilization in body (focal length input in menu)
  • M and Av exposure
    • Diaphragm must be in MANUAL mode
    • No aperture information in EXIF (K3-iii allows manual input of aperture)
  • Settings have to be changed in the menus and their location is camera dependent
    • Allow use of Aperture Ring
    • Green button to Tv-shift in M and A mode
    • K3-iii (2021) added support for exif in aperture for K mount lenses[28]
      • Set Length Input on Startup to On
      • Set Using Aperture Ring to On
      • Set Aperture Info Record to On

Use in other systems:

Due to the abundance of good available examples and relative low price, Takumar lenses have been used in other camera systems [29][30][31]. In general due to the flange focal distance of M42 cameras and lenses (45.46mm), it can be adapted to any camera with shorter distance without optical correction but just some extension tube; in system that have longer flange distance, however, an optical element is needed to compensate for this which can induce optical aberrations. Quality adapters are available from many suppliers.

A summary of the existing DSLR and mirrorless camera systems and compatibility of Takumar (M42) lenses is shown below

Lens mount Optical correction? Focus confirmation Metering Crop factor Notes
Canon EF/EOS

All autofocus SLRs

No Needs chip Yes 1x-1.6x M and Av modes. Rear of some lenses may collide with mirror of the 5D.
Canon EF-M

Mirrorless

No Needs chip Yes 1x-1.6x M and Av modes; lenses must be in Manual Diaphragm
Micro Four-Thirds Mirrorless No Not needed Yes 2x No focus-assist, but you won't need it with live-view magnification.
Nikon F

All autofocus SLRs

Yes Yes Sometimes 1x-1.5x No metering with cheaper SLRs.
Nikon Z

Mirrorless

No Yes Yes 1.5x M and Av modes for metering
Sony Alpha / Minolta AF No Needs chip Yes 1x-1.5x Needs a chip to get in-body stabilization working.
Sony E-mount No Yes 1.5x Need to set camera to shoot without a lens.
Fujifilm X-Series No Yes: MF Assist / Focus Peak Highlight YES 1.6 Need to set camera to shoot without lens
Fujifilm G-Series No Yes: MF Assist / Focus Peak Highlight YES ~0.8
Vignetting possible
Need to set camera to shoot without lens



References

  1. Takuma Kajiwara bio at Wikipedia
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Gerjan van Oosten, 2021, "The Definitive ASAHI PENTAX Collector's Guide 1952-1977". 2nd Edition ISBN978-90-9034415-7
  3. Early PENTAX TAKUMAR Lenses by Frank Mechelhoff 2005 at Classic Camera.de
  4. 4.0 4.1 Takumar Field Guide blog and site by David Rounsevell
  5. 5.0 5.1 Development of the Asahiflex by Gerjan van Oosten - Article in Asahi Optical Club Nederland Magazine #10
  6. 6.0 6.1 Lenses for the Asahiflex by Gerjan van Oosten - Article in Asahi Optical Club Nederland Magazine #11
  7. The "Fast Telephoto Story" (1953-1984) Takumar 85mm f/1.8 by Frank Mechelhoff
  8. AutoTakumar catalogue by Asahi showing Auto takumars and Preset Takumars, mostly in Japanese at Paul Provencher's Pentax books and manuals
  9. 9.0 9.1 9.2 Herbert Keppler, 1974. The Pentax Way. 8th ed ISBN 0-240-50889-0
  10. Evolution of the M42 mount by stevebrot at pentaxforums.com
  11. 11.0 11.1 Walter D Emanuel. 1979. The Asahi Pentax Guide, 21st ed, Focal Press ISBN 978-02-4044874-9
  12. List of screw mount lenses at Paul Provencher's Pentax books and manuals
  13. 13.0 13.1 Takumar 6x7 Field Guide blog and site by David Rounsevell and Gordon McLellan
  14. Pentax 6x7 lens List by Denis Baron at MIT
  15. Bertele E. 2019 LUDWIG J. BERTELE A Pioneer of Geometric Optics. Vdf Hochschulverlag ETH Zurich. ISBN 9783728139559 ETH Zurich, abstract
  16. Smith G.H. 1998 Practical Computer-Aided Lens Design. Willman Bell. ISBN 9780943396576 Available from publisher WillmBell
  17. Wang J, Henningson V. 2013. An Analysis of Residual Radiation in Thoriated Camera Lenses. Department of PhysicsSchool of Engineering SciencesRoyal Institute of Technology (KTH)Stockholm, Sweden, 2013
  18. Wirtenson, G R; White, R H, 1992 Effects of ionizing radiation on selected optical materials: An overview. Technical Report Lawrence Livermore National Lab., CA, USA. doi:10.2172/10178461
  19. Robert C. McMillan & Steven A. Horne: Eye Exposure from Thoriated Optical Glass U.S. Army Mobility Equipment R&D Center. Date unknown
  20. Comparison of the Double Gauss and Sonnar lens designs at Pencil of Rays, Lens design blog
  21. Takumar field guide 50/1.4 Super Takumar 8 element by David Rounsevell
  22. US patent "LARGE APERTURE SEVEN-LENS OBJECTIVE LENS SYSTEM" Inventors: Tomokazu Kazamaki, Yasuo Takahashi Asignee: Asahi Optical Corp. 1966
  23. Takumar field guide 50/1.4 Super Takumar 7 element by David Rounsevell
  24. Pentax Ricoh SMC PENTAX-FA 50mm F1.4
  25. Pentax Ricoh HD PENTAX-D FA* 50mm F1.4 SDM AW Lens
  26. Use M42 lenses in Pentax DSLRS by Adam at pentaxforums.com
  27. Manual Metering on Pentax DSLRs with Manual and Automatic Lenses by Adam at pentaxforums.com
  28. Using K and M Lenses in K3-III article in PentaxForums
  29. Compatibility of M42 with DSLR systems by Lewis Collard
  30. Adapting lenses to Micro Four Thirds at Micro Four Nerd Blog
  31. Vintage Lenses on Modern Cameras: Using M42 on Fujifilm X by Ritchie Roesch at fujiXweekly.com

Bibliography

  • Gerjan van Oosten, 2021, "The Definitive ASAHI PENTAX Collector's Guide 1952-1977". 2nd Edition ISBN978-90-9034415-7
  • Herbert Keppler, 1974. The Pentax Way. 8th ed ISBN 0-240-50889-0
  • Walter D Emanuel. 1979. The Asahi Pentax Guide, 21st ed, Focal Press ISBN 978-02-4044874-9
  • Lens literature at Kim Coxon's manual site
    • Lenses for the Honeywell Pentax. Literature from Honeywell. 10/1965
    • SMC Takumar operation guide. Asahi Pentax 1973
    • Asahi Pentax Complete System. Asahi Pentax, 1969
    • Honeywell Photographic Products. (Sales Brochure). Honeywell, 1969

Links