Identifying a lens mount (OLD version)

This is the old (pre-2022 version of this guide, which is kept available in case some links should still point this way.
The new version is available here.

22.9.2020: Added EXA mount
01.10.2020: Added Icarex BM mount

I – like many of my peers – hang out at various online forums where people often post pictures of a lens and ask: “Can you help me identify this lens mount?”.

This article is intended to help with the task of identifying lens mounts. Please, be aware that there are more than a hundred lens mounts (currently Wikipedia lists 108), and that this article cannot cover them all. Instead, this article will try to cover as many as possible (and I will keep adding to the article as I gather more samples), making this article quite lengthy. Nevertheless, there are some limitations:

  • Emphasis is placed on helping identify those lens mounts which people are most likely to come into contact with, especially high-volume still camera mounts.
  • As a corollary, medium format systems will be omitted for now. (As medium format digital becomes more common, I might add them at a later date.)
  • Also, new mounts are not covered in equal detail (as people are more liable to need help with identifying old/legacy mounts).

This article is a companion piece to the Introduction to lens mounts -article, so if you feel you want to learn more about lens mounts, head over there first (or later).

Table of Contents

Basics of identifying a lens mount

Before we go any further, I’m assuming you have already tried searching online. Quite often, that is all you need. Start by typing in the name on the side of the lens or the front ring of the lens into the search engine of your choice and hit enter.

Nevertheless, beware that while major-brand lenses (Canon, Konica, Minolta, Nikon Olympus, Pentax, Pentacon, Rollei, Olympus, etc.) were typically only made for the proprietary mount, minor differences in spelling can make all the difference.

An issue of a totally different caliber are third-party and rebranded lenses (Helios, MIR, Porst, Sigma, Soligor, Tamron, Tokina, Vivitar etc.), for which it was customary to manufacture the same lens with several different lens mounts, often without this change being reflected in the lens’ name.

If you’re still confused after doing a web search, we need to start with the basics: Identifying the mount type (bayonet, breech-lock or thread-mount). See the illustration of these three basic types below.

Left-to-right: Thread mount, (obvious) breech-lock mount, and bayonet mount.

A thread or screw-mount has threads, using which the lens is screwed into the camera. If your lens is a thread mount-lens, continue its identification here.

The idea with breech-lock mounts, is that the lens is inserted straight into the camera (in what will be its final orientation), after which a locking ring is tightened. Breech-lock mount lenses can be easily and positively identified if the lens’ mount has a locking ring which can be rotated (typically between 30 and 90 degrees). If your lens has a rotatable locking ring, you’ve positively identified your lens as a breech-lock mount, jump here.

(Besides these, there are breech-lock mounts which have a locking-ring mounted on the camera (and may thus be equivocal). These are listed under bayonet mounts.)

Finally, there are bayonet mounts, which all rely on a twisting motion (around the lens optical axis) to lock a lens in place. Jump here for identifying your bayonet mount.

Thread-mount lenses

Thread mount lenses are similarly relatively easy to spot as a group, because of the highly prominent existence of threads on the lens mount. That said, there are quite a lot of these, and the first step you need to do in order to identify the mount is to pick up a measurement tool (if you have a caliper, all the better).

Fujinon 55 mm f/1.8 lens’ (M42) mount being measured with a caliper.
Notice that the reading is roughly 41,85 mm (my M42 lenses vary between 41,77 and 41,92 mm).

Often it is enough to measure the diameter of the mount, but in some cases it is also necessary to measure or test the thread pitch (distance between ridges in thread).

47 mm diameter:

Most probably a T-thread mount (47 mm with thread pitch of 0,75 mm). The T-thread-mount is not to be confused with the T-mount (42mm diameter).

Tokyo Koki (Tele-Tokina) 135 mm f/2.8 T-thread mount lens.

The idea of the T-thread is not to be mounted directly on a camera, but to be screwed into an adapter which would then fit the camera (similar in idea to the more well-known adaptall-bayonet). Your best bet for mounting a T-thread lens, is to hunt down an original adapter-ring, such as the T-thread-to-Minolta SR adapter pictured below.

T-thread to Minolta SR adapter. The adapter is screwed onto the lens, and the set-screws tightened. Note, that there is no interface between lens and body.

44 mm diameter:

Interesting, as there is no lens mount with a 44 mm diameter. What you might have there is a normal M42 (42 mm diameter) lens, with an adaptor ring for the Miranda cameras’ internal 44 mm thread stuck on it. Try to see if you can unscrew it?

42 mm diameter:

Most probably a classic M42 thread mount, but watch out, because it might also be a T-mount or one of its variants. To make sure, measure the thread pitch. The thread pitch of M42 is 1 mm (M42x1.0), whereas the thread pitch of the T-mount is 0,75 mm (M42x0.75).

Some combinations of lens and caliper do not allow measuring the thread pitch. In this case (Pentacon 29 mm f/2.8 and cheapo caliper) the threads are so deeply recessed and the caliper’s inside measurement head so broad, that they do not fit. In such cases only a gentle testing can answer the question.

Note! If you cannot measure the thread pitch, try very gingerly screwing the lens into a M42 adapter (or camera) – if it fits, it’s M42. If it jams part-way (don’t use force!), it’s probably a T-mount. If you feel apprehensive toward such a direct experiment, you can also use a lens (back) cap from an M42 lens, but remember that the plastic may have worn, thus giving a false positive.

The M42 is the quintessential old-school lens mount. Variously also known as the Praktica- or Pentax screw (or mount) due to its most well-known users. There are several variants of the M42 mount, offering several alternative interfaces, so have a good look at the M42 section

The T-mount, while not to be mistaken for the T-thread mount (see above), is also an intermediary mount (similar in idea to the more well-known adaptall-bayonet), so your best bet for mounting a T-mount lens is to hunt down an original adapter-ring.

40 mm diameter

Note! Rare. Recheck your measurements, but if you’re sure, go on…

The M40 (thread pitch 1.0 mm) thread mount was used by the Praktiflex-camera (1939-1947) and only a handful of lenses were ever produced for it – most of them made by Carl Zeiss and Schneider-Kreuznach. Even though the camera is rare (partially due to WWII), its quality lenses may entice the entrepreneurial aficionado to build a DIY adapter.

39 mm diameter

The land of (potential) confusion. There are basically four types of thread-mount lenses with a diameter of 39 mm.

Firstly, there are enlarger lenses (M39x1.0), which are easily identified by the lack of any focusing mechanism. Enlarger lenses are well-known to anyone who’s ever developed their own pictures, and while not made for cameras, are potentially usable for everything from macro work to close-to-normal use, assuming an adapter with helicoid or adapter and bellows.

Secondly, there are the original Leica M39 thread mount lenses for early rangefinders by Leica and everyone who copied the design (including Canon, FED, Zorki…). This mount has a 26 TPI thread pitch, which roughly translates to 1/0.98 mm, making these lenses hard to distinguish from M39x1.0 lenses. The clearest indicator is a relatively shallow FFD (28,8 mm).

This mount has many names and is variously referred to as “Leica thread mount”, “Leica screw mount” (and acronyms LTM and LSM) as well as “L39” or “M39”. There is a wide variety of lenses available for this mount, and due to their sometimes high quality and uniformly modest size (rangefinder lenses), they are attractive to lens hackers everywhere. Ready-made adapters are widely available for all mILC’s as well as for adapting these lenses to the later Leica M-mount.

Thirdly, there is also the Zenit M39 mount, which is a standard M39x1.0 screw, but will not work correctly with a LSM/LTM/L39 adapter due to a significantly different flange focal distance (45,2 mm). This lens mount was used by early Soviet Zenit SLR’s (later Zenit SLR’s migrated to using the M42 mount)

These lenses are neither rare nor commonplace. If you have one and want to mount it, the bast way is a combination of using a regular LTM adapter and a 16,4 mm (M39->M39) distance ring (these are available online). Mounting such a lens directly on an LTM adapter would fit, but as the difference between designed and actual flange focal distance would be a whopping 16,4 mm, it is quite likely the lens would be entirely unable to focus.

Finally, there is also the Paxette -mount, used solely by the Braun Paxette cameras, and here the situation is similar to that of the Zenit M39 mount, except that DIY-adapters are the only route (to my current knowledge), due to the 44 mm FFD of the Paxette -mount. See more here.

N.B! The M39 has also been used for non-lens optical arrangements, such as the Leitz Visoflex I. Not every optical instrument you find fitted with an M39 thread is necessarily a photographic lens.

37 mm diameter

Rare. Used by the first generation of Asahiflex (Pentax) cameras.

25,4 mm (1 inch) diameter

These lenses are typically C- mount lenses used in 16 mm motion picture cameras, microscopes and industrial cameras. The flange focal distance of the C-mount is only ≈ 17,5 mm and thus longer than that of almost all current mILC cameras (Nikon Z being the sole exception). As the image circle of these lenses is limited by design, their adaptability on current mILC’s is very limited.

On the other hand, should you have a Samsung NX mini (FFD: 6,95 mm; sensor size 13,2×8,8 mm), Pentax Q (FFD: 9,2 mm; sensor size 7,44×5,58 mm) or Nikon 1 (FFD: 17 mm; sensor size 13,2×8,8 mm) camera body, C-mount lenses are obviously interesting

N.B! There is also a variant of the C-mount (going under the name CS-mount), with an even shorter FFD of ≈12,5 mm.

24 mm diameter

M24x1.0 is the characteristic of the Soviet Narciss miniature interchangeable lens camera’s mount. Designed for 16 mm film, and an image size of 14×21 mm, these lenses are of limited utility to anyone using a sensor larger than micro four thirds. I have yet to find accounts of successful adaptations (If You have, please notify me). In any case, few of these cameras (or lenses) made it far outside the iron curtain (I’ve seen some in Finland). More info here.

15,88 mm (0,625 or 5/8 inch) diameter

These lenses are D-mount lenses, designed for 8 mm film cameras. As with C-mount lenses (see above), these lenses are limitedly useful on modern current mILC’s, but some enterprising adaptations have been made.

Even smaller thread mounts…

…can be found in various optical instruments – ranging from CCTV -camera lenses to various industrial applications. Due to typically minuscule image circle and very shallow flange focal distances, the adaptability of such lenses is practically non-existent.

Obvious breech-lock lenses

The weight here is on the ‘obvious’ because there are some breech-lock lenses, which you cannot readily identify as such, because the locking collar or ring is not on the lens but on the camera. So the question you need to ask here is: is there a ring on the lens’ mount which you rotate lock the lens in place?

If no, skip to bayonet mounts.
If yes, the we’ve narrowed it down significantly from the beginning.

Canon R, FL and FD lenses have a clearly prominent breech-lock locking ring at the base of the lens. The difference between FL and FD is also cearly visible in the number of levers: One (FL) or two (R or FD). The Canon R mount is relatively rare, and can be differentiated by that its two levers are grouped together between 12 and 1 o’clock. For the difference between FL and FD mounts, see picture below.

Left: Canon FL mount (on FL 55 mm f/1.2)
Right: Canon FD mount (on FD 55 mm f/1.2)

Icarex BM lenses are relatively easy to identify as they have only two openings in the breech-lock ring (one narrower, one wider). See picture below and skip to section about details on the mount.

Icarex BM -mount (on Zeiss Skoparex 35 mm f/3.4)

Contax G lenses are technically breech-lock lenses, but that may be hard to spot, both as the locking ring cannot be rotated unless the lens is mounted on a camera (or adapter), and as the mount evidences several features generally associated with bayonet lenses. Contax G lenses further have a slot-drive screw for body-driven autofocus and electronic contacts, making the Contax G-mount not only a sleeper bayonet, but a highly distinct design. See picture below and more details in the Contax G-section below.

Carl Zeiss Sonnar 90 mm f/2.8 in Contax G mount

Does your lens have an obvious breech-lock locking ring, but is not one of the above? Congratulations, you have something quite unusual on your hands. Please send me a message or leave a comment.

That’s it. This is not to say that there are not other (relatively obscure) breech-mount lenses for still cameras, but they are not obvious breech-mount lenses in that their locking ring is mounted on the camera (not the lens), such as Petriflex and Praktina (for 35 mm film) or Pentacon Six and Kowa Six (medium format film)

Bayonet lenses

On the inherent difficulties of identifying bayonet mounts…

While the above categories (breech-lock and thread) have tried to be both exhaustive and mention every type of mount (even when they are exceedingly rare or only limitedly adaptable), the same cannot (at least, yet) apply to this, final category. The simple reason is, that there are so many bayonet mounts…

Not only is the sheer number of bayonet mounts daunting, many of these have further variations, which – while typically somewhat compatible – make trait-based identification difficult. But we have to start somewhere…

The best way to approach identifying bayonet mount lenses is by cataloging the characteristics of the interface. Next, have a look at these traits:

  • is the bayonet male or female?*
  • how many prongs (or openings) does the bayonet have?
  • Is the locking mechanism based on an indentation in the lens base or in one of the bayonet prongs, or is it based on a locking pin?
  • are there notches in the prongs, and if so, where are they (what o’clock)?
  • is there a notch in the lens mount base (for locking)? At what o’clock?
  • does the mount have electronic contacts, how many, where are they?
  • does the mount have pins or levers**, how many, and where

* There are two types of bayonet mount, which I (in accordance with common parlance in other fields) will refer to as male bayonets and female bayonets. With male bayonets the lens’ mount has prongs which are inserted to corresponding openings in the camera, whereas with female bayonets the prongs are on the camera end (and the lens’ mount has the openings.)

** Pins are things sticking out of the lens mount which you can depress (they go in and pop back out), while levers move (or are designed to move) sideways (radially from the optical axis). Locking pins are rigid pins used for locking the lens in place.

Once you have those basics sorted, go through the questions outlined below, and if you then are left with multiple options, you’ll just have to click the links for a final visual confirmation.

Caveats: Several mounts (most notably Nikon F and Pentax K) have had several iterations, leading to differences within one otherwise interchangeable mount. For instance, some Pentax K lenses have electronic contacts where others do not. When I have been able to cover all iterations (as with Nikon F and Minolta SR), I have done so. When not, I have tried to make that clear as well).

Female bayonet mounts

Female bayonet mounts are luckily quite rare. “Luckily” not because there’s anything inherently wrong with them, but because their rarity makes identification easy. In fact (among even slightly common lens mounts) there are only four: Canon FDn, Miranda Bayonet, Tamron Adaptall and Topcon bayonet.

The Miranda Bayonet (picture in progress) is easy to distinguish, as it has four prongs/openings instead of the normal three, whereas lenses for the Topcon bayonet (picture in progress) can most easily be distinguished by that Topcon bayonet lenses lack an aperture ring (the aperture ring is on the camera’s end of the mount).

Canon FDn and Tamron Adaptall can be easily distinguished visually.

Left: Canon FDn / Right: Tamron Adaptall 2

The picture above shows the most obvious differences, namely:
[1] the Canon FDn’s rather pronounced unlocking clamp (or button), especially compared by the relatively small unlocking prong of the Adaptall mount [3]
[2] The FDn-mount’s two levers for lens-body communication, compared with the one recessed lever deep in the base of the Adaptall -mount [4].

Male bayonet mounts

All bayonet mounts are characterised by that they (once twisted into place) lock the lens onto the body. This locking typically is achieved by a protrusion, pin or hook in the camera, which latches onto or into a hole or groove in the lens. Sometimes, the roles are reversed and the lens seems to have a pin, which might lock into a hole on the camera. Finally, sometimes the locking mechanism is not directly obvious.

System for identifying male bayonet mounts

The placement of these pins, holes, notches or grooves is the most definite characteristic of various lens mounts and will be crucial to our method of identifying the lens.

Start by identifying whether the lens has a locking notch (a notch in one of the bayonet prongs), a locking groove (a hole or groove in the base of the lens mount), a locking pin (a pin in the lens mount which might be used for locking) or none of the above.

(See picture below for examples)

Top row, locking notches. Middle row, locking grooves. Bottom row, locking pins (or what could be locking pins).
(Featured mounts (alphabetical): Contax/Yashica, Konica AR, Minolta SR, Nikon F, Olympus OM, Pentacon Six, Pentax K, Praktica B, Praktina

Next, put the lens face down (mount up) in front of you on the table, and orient the lens’ upside (what would in landscape mode be facing up) at 6 o’clock (towards you). I know that this results in a view of the lens which is 180 degrees different from what you’re used to finding online, but by putting the lens top towards you, you can make sure that the lens is oriented correctly, and as some of the differences are so small that 15 degrees (half an hour on your watchface) makes a big difference.

Konica AR 35 mm f/2.
(1) Highlighted red line shows lens’ upside (notice that both focus ring and aperture ring are unreliable indicators of “up”, because they rotate).

Now, lean forwards until you view the lens mount straight from above, and imagine a clock-face onto the lens mount and make a note of the position (at what o’clock) of the groove, notch or pin .

The very same Konica 35 mm f/2, with upside of lens at 6 o’clock.
Note locking notch at ≈ 3 o’clock

Using this simple tool you can identify almost all bayonet mounts, but remember that many mounts have different variations, so make sure to have a look at the detailed descriptions.

Oh, one more notable characteristic: When lenses have electronic contacts these need to be in solid contact with their counterparts on the camera body. Typically, this is assured through that the electronic contacts on either the camera body or on the lens are spring-loaded (pushed outward by a spring, which allows the contact to withdraw when coming into contact with their counterparts). In some mounts, that spring-loading takes place in the body and in others at the lens-end, making this another useful characteristic. Subsequently, I will refer to electronic contacts as ‘spring-loaded’ if their spring-loading is on the lens (not on the body)

Has locking groove at…

  • 3 o’clock ==> Canon EF, Canon RF, Contax G, Four Thirds, Fujica X, Micro Four Thirds, Nikon F, Nikon Z and Sony/Minolta A
    • Yup, definitely the most popular arrangement, but there are subtle differences, which allow conclusive identification.
    • Nikon F:
      • Locking groove in the base of the mount (on the flange)
      • Three bayonet prongs
      • Only one lever, that operates aperture (some of newest lenses: no lever)
      • Electronic contacts (spring-loaded) between 5 and 7 o’clock, facing out from optical axis (AF, AF-D, AF-S, AF-P), or no electronic contacts (Pre-Ai, Ai, Ai-s)
      • Slot-drive screw possible (AF&AF-D lenses) at about 10:45
      • For more details, jump to the Nikon F-section
    • Nikon Z:
      • 11 Electronic contacts between 5 and 7 o’clock, facing toward rear of camera.
      • Locking groove in base of mount (on the flange)
      • Four bayonet prongs
      • No levers, no slot-drive screw
    • FT (four thirds):
      • 9 Electronic contacts between 11 and 1 o’clock, facing toward rear of camera.
      • Locking groove in base of mount (on the flange)
      • Three bayonet prongs
      • No slot-drive screw, no levers
    • MFT (micro four thirds):
      • 11 Electronic contacts between 11 and 1 o’clock, facing toward rear of camera.
      • Locking groove in base of mount (on the flange)
      • Three bayonet prongs
      • No slot-drive screw, no levers
      • N.B! MFT is a smaller version of FT, with two extra contacts.
    • Canon EF and RF:
      • Electronic contacts between 11 and 1 o’clock, in two tiers, facing towards rear of camera.
      • EF mount has maximum of 7 contacts, RF mount has 12
      • No slot-drive screw
      • Locking groove in base of mount (on the flange)
      • No levers
      • Three bayonet prongs
      • For more details on the Canon EF mount, look here.
    • Fujica X:
      • No electronic contacts, no slot-drive screw.
      • Locking groove in base of mount (on the flange)
      • Two levers (stop down and aperture indicator)
      • Three bayonet prongs
    • Sony / Minolta A:
      • Electronic contacts between 5 and 7 o’clock, facing towards back of camera.
      • Slot-drive screw possible (some lenses) at about 1:30
      • One lever (or no lever on newest lenses)
      • Three bayonet prongs
    • Contax G:
      • Electronic contacts between 10 and 12 o’clock
      • Locking groove on rearmost (camera-facing) end of bayonet
      • Slot-drive screw at 12:30 o’clock
      • No levers.
      • Four bayonet prongs
      • For details, look here.
  • 9:45 o’clock ==> Pentax K, Praktica B or Sigma SA
    • Praktica B:
      • only one lever
      • three (and always three) (spring-loaded) electronic contacts between 1:30 and 2:30
    • Pentax K
      • One or two levers
      • Various constellations of electronic contacts (up to 7, but rarely three) on the mounting flange. May have two further contacts on rear of lens (inside flange)
      • May have slot-drive screw for body-driven auto-focus
    • Sigma SA
      • Three-pronged bayonet
      • No levers
      • 10 electronic contacts between 11 and 1 o’clock
  • 10 o’clock ==> Sony E and FE
  • 10:30 o’clock ==> Leica L or Fujifilm X
    • Leica L
      • Four bayonet prongs
      • 10 Electronic contacts between 5 and 7 o’clock
    • Fujifilm X
      • Three bayonet prongs
      • 10 electronic contacts between 11 and 1 o’clock

Has locking notch at …

  • 2:30 o’clock ==> DKL
  • 3 o’clock ==> Konica AR or Contax G
    • Contax G:
      • Has electronic contacts
      • Has slot-drive -screw
    • Konica AR:
      • No electronic contacts
      • No slot-drive screw
  • 5:30 o’clock ==> Contax/Yashica
  • 6:30 o’clock ==> Minolta SR
  • 11:30 o’clock ==> Rollei QBM

Has locking pin at …

  • 3:30 o’clock ==> EXA(kta)
  • 4:30 o’clock ==> Olympus OM (note, pin is hidden under bayonet prong)
  • 6 o’clock ==> Pentacon 6, Praktina

Has none of the above (at least you could not find it):

  • The Olympus OM mount’s locking pin can be hard to spot if you do not know where to look for it.

Visual identification and mount descriptions

The following headings will (for the part that I’ve had a chance to write them) have at minimum a clear guide for the conclusive identification of the various mounts. Also – when possible – I’ve tried to give details on all substantial variations, and when I cannot, I’ve tried to find a good source for you to continue your explorations.

In the case of some mounts, I’ve also tried to give more detail as well as comment directly on adapting these lenses. With some mounts, I have an article dedicated to that mount, and in those cases I’ve supplied you with an link to said article.

Adaptall 1 & 2

To be added later, sorry.
If you want to support this page, be in touch and send pictures of lens mounts.


To be added later, sorry.
If you want to support this page, be in touch and send pictures of lens mounts.

Canon EF-family

Canon EF 50 mm f/1.8 MkI

Key characteristics of the mount of Canon EF lenses:
[1] Locking groove at 3 o’clock.
[2] Three unsymmetrical bayonet prongs, all with straight edges.
[3] Electronic contacts between 11 and 1 o’clock.
[4] Red ball for helping lens alignment at mounting (EF-S lenses have a small white square in a slightly different position)
[5] Metal lens mount (black plastic on some cheaper lenses)

The inscription at six o’clock is not a serial number, but can instead be used to identify manufacture location and date. This lens having been manufactured at Canon’s Utsunomiya (U) factory in may (05) 1988 (C). On more modern (starting 2008) lenses, the syntax of this code has changed (but its purpose remains). See more here.

Basics of the EF mount
The Canon EF -family of lens mounts are composed of the original Canon EF (electronic focus) mount (starting 1987), and its derivatives: The EF-S mount for crop-sensor dSLR’s (starting 2004) and the EF-M mount for the Canon EOS M-series mILC’s (Starting 2012). All have physically the same mount, but inter-system compatibility is limited. While EF and EF-S mount have the same flange focal distance, EF-S lenses are not designed to cover a full-frame sensor. EF-M lenses are designed with a significantly shorter flange focal distance, and while EF-S and EF lenses can be used on EOS-M cameras using a suitable adapter (basically, a smart adapter), EF-M lenses can not be used on EF or EF-S bodies.

Besides Canon, Canon EF lenses have been manufactured by practically all third-party lens manufacturers. While Canon’s main focus seems to have shifted to its mirrorless mount (Canon RF), the days of the EF -mount are not yet numbered, especially as the EF mount lately has broadened its spectrum of application from still to video cameras.

Adapting Canon EF (and EF-S) lenses:
With Canon EF (and EF-S) lenses having a flange focal distance of 44 mm, they can relatively easily be adapted to all mILC’s, with one proviso: As Canon EF lenses are fully electronically controlled, controlling the aperture of Canon EF lenses necessitates a smart adapter (A dumb adapter could be used to mount an EF lens at the correct distance, but the aperture would always remain wide open). Naturally Canon EF lenses can also be used on Canon R -mILC bodies with Canon’s own EF-to-RF adapter.

Canon FD

Note! There is a more comprehensive article on the Canon FL, FD and FDn mounts, so this chapter will only concern itself with identification.

Alike its predecessor, the FD mount is a breech-lock mount, which means that lenses are inserted straight into the camera, and a locking ring is turned to attach the lens. That locking ring is one of the unmistakeable characteristics of the FD mount. The picture below shows the other characteristics. Please also compare with the characteristics of the Canon FL mount to avoid confusion.

Canon FD 35 mm f/2

Key characteristics of the mount of Canon FD lenses
[1] Breech-lock locking ring, rotates approximately 90 degrees (when not connected to a camera or adapter).
[2] Alignment pin.
[3] Stop-down lever.
[4] Aperture indicator lever.

Canon FDn

Note! There is a more comprehensive article on the Canon FL, FD and FDn mounts, so this chapter will only concern itself with identification.

The Canon FDn (new FD) mount is somewhat odd, in that it is a conversion of the breech-lock FD mount into a bayonet mount, while retaining compatibility (both backwards and forwards). Also, it is characterised by that it being a female bayonet mount (the prongs are on the camera, not the lens). These factors make it relatively easy to identify. Even so, the picture below shows the notable characteristics of the FDn mount.

Canon FDn 135 mm f/3.5

Key characteristics of the mount of Canon FDn lenses
[1] Female bayonet mount with three openings.
[2] Lens release button (pops out when lens locks on body/adapter).
[3] Alignment pin.
[4] Stop-down lever.
[5] Aperture indicator lever.
[6] Bayonet activation pins (bayonet is locked until body’s or adapter’s prongs or lens cap depresses these).

Canon FL

Note! There is a more comprehensive article on the Canon FL, FD and FDn mounts, so this chapter will only concern itself with identification.

Alike its successor, the FL mount is a breech-lock mount, which means that lenses are inserted straight into the camera, and a locking ring is turned to attach the lens. That locking ring is one of the unmistakeable characteristics of the FL mount. The picture below shows the other characteristics. Please also compare with the characteristics of the Canon FD mount to avoid confusion.

Canon FL 85 mm f/1.8

Key characteristics of the mount of Canon FL lenses:
[1] Breech lock locking ring, rotates approximately 90 degrees (when not connected to a camera).
[2] Alignment pin.
[3] Stop-down lever.

Canon R

This refers to the Canon R-mount (1959-1964), which is the predecessor to the Canon FL -mount. The Canon R-mount is relatively rare but has striking similarities with the Canon FL mount. Sadly, as I do not have a Canon R lens on hand, I cannot offer you a picture, but one is available here.

The rest of part will be added later, sorry.

Canon RF

Canon RF refers to the new mount Canon has adopted for its new line of mirrorless camera bodies. Due both to the existence of a previous mirrorless lens mount (EF-M) and the fact that RF more commonly refers to “rangefinder”, there is some risk of confusion.

Otherwise, this section will be added later, sorry

Contax G

Key characteristics of the Contax G -mount:

Carl Zeiss Sonnar 90 mm f/2.8 T*

[1] Locking notch at 3 o’clock (but, unusually, on the rearwards facing end of the “bayonet”, not on the flange and not on a bayonet prong)
[2] Bayonet-like construction* with four prongs
[3] Bank of electronic contacts
[4] Slot-drive screw
[5] Bulge (housing gearing for slot-drive)
[6] Pins for detecting mounting on camera (or adapter)

*While technically a breech-lock mount (you insert the lens straight into the camera, then twist a ring on the lens to mount it securely), the Contax G mount evidences a great many bayonet-like features. Not only does it seem to have what looks like an obvious four pronged bayonet construction, it also has a locking notch (although whether it should be classed as a locking notch or locking groove is debatable), which also is a typical bayonet trait. In one sense, the Contax G mount has it all (except for threads).

Basics of the Contax G -mount
(N.B! One day, the Contax G mount may deserve a page of its own. For now, some details will be given here.)

‘Contax’ is undoubtably one of the most legendary names in photography. First used in 1932 for a groundbreaking 35 mm camera made by Zeiss Ikon, during the more recent decades, the name Contax has made several reappearances in photography hardware which (while certainly holding onto something of the original Contax legacy) have been both geographically and administratively quite far removed from the name’s origins. Since the 70’s, the name Contax was first used for SLR’s manufactured in a Zeiss-Yashica (Kyocera) co-operation, and later (1990’s) for the Kyocera-built Contax G autofocus, interchangeable lens rangefinders.

The main strengths of the Contax G system was the combination of Carl Zeiss rangefinder lenses with a rethinking of what the rangefinder camera could be at the end of the millennium. The resulting Contax G1 (1994) and G2 (1996) cameras, aimed to combine autofocus and modern metering with the appeal of the rangefinder camera. Having never actually shot a roll of film with one, I do not want to venture a judgment on how they faired.

That said, the Zeiss-designed lenses obviously have been a big part of whatever appeal the system had and still has. Problematically, due to their design (mount, flange focal distance, etc.), re-use of these lenses on other systems has been a challenge, until the advent of mirrorless interchangeable lens cameras.

Adapting Contax G lenses:
Thanks to their shortish flange focal distance (29 mm) and their relatively complex mount, Contax G lenses have not been reusable on other systems until the advent of mILC’s. Another point against their adaptability has been that Contax G lenses – while having a manually controlled aperture – have no focusing ring. With Contax G lenses being body-driven AF lenses, this is not unheard of (while certainly somewhat unusual).

In practice this means that for Contax G lenses to be usable, the adapter has to be able to drive the slot-drive focus screw – either by allowing manual-driven focusing or by containing a small AF motor. Both arrangements exist and are certainly workable, but do demand some millimetres to play with.

I’ve only managed to gather experience of Contax G lenses with a manual adapter, and my take is that, while (as said) workable, the arrangement is far from optimal. Given, that the ring used to drive the slot-driven AF is by necessity very close to the camera body, the arrangement is ergonomically dismal (see pic below). If you’re in the lucky position to own more than one Contax G lens, I’d heartily recommend an adapter which makes the AF function as it should.

Sony a7R, manual adapter and Carl Zeiss 90 mm f/2.8 (Contax G)
[1] Manual focusing ring (drives slot-drive screw)
[2] Breeck-lock locking ring
[3] Aperture ring (full clicks only)

Contax / Yashica (C/Y)

The Contax / Yashica (C/Y) mount is just one of the many mounts of the film era, but due to some factors, it is highly interesting. We’ll have a short look at the reasons later, but first, let’s make sure we can identify it correctly.

Carl Zeiss Distagon 28 mm f/2.8 AEJ (and yes, it has some oil on the blades)

Identifying the C/Y mount
[1] Locking notch at 5:30
[2] Three-pronged bayonet mount, two straight edges, three tapered edges, and one very shallow edge.
[3] Aperture indicator lever
[4] Stop-down lever
[5] Place where (if this was an MM lens) the indicator prong would be

General information on the C/Y mount:
The mount was co-designed by Zeiss and Yashica. Yashica wanted to up their game (against their Japanese rivals), while Zeiss needed an outlet for 35mm photographic lenses (beside medium format and cinema lenses). Zeiss also licensed the name Contax for use by Yashica for the flagship line of SLR cameras. Resultingly, both ‘Contax’ and ‘Yashica’ cameras for the C/Y mount were in fact manufactured by Yashica.

The mount (as well as the Contax RTS and Yashica FX-1 bodies) were introduced in 1975 and while one could say its mainstream development ceased in the late 80’s (with Yashica’s ill-fated introduction of its line of AF SLR’s and lenses), further development under the Contax brand continued until 1998 (the Contax Aria). By that time, however, the Contax line of cameras had quite clearly become a niche product (albeit a prominent niche).

While the C/Y mount is most well known for its impressive lineup of Carl Zeiss lenses, these were – by far – not the only lenses available for the mount. Firstly, also Yashica were renowned for their lens design and manufacturing, and Yashica themselves produced two lines of lenses for the Contax/Yashica system, named ‘ML’ and ‘DSB’. Of these, the ML line was the more prestigious (featuring multi-coating), whereas the DSB-lenses were more intended for the plebes.

Furthermore, a great number of third-party lens manufacturers offered their designs also in the C/Y mount, but (and, please, take a pinch of salt now) while a great many third-party lenses were offered for the C/Y mount, these are relatively rarely available on the secondhand market. My personal suspicion is, that those who photographers who opted for the Contax-Yashica system, with its ‘premium’ image, were less inclined to then tarnish their camera with off-brand optics.

Adapting C/Y -mount lenses:
As is typical for optics of this era, the lenses are fully manual, thus offering themselves for easy adaptation. Also, not uncommonly, adapting C/Y lenses for use on dSLR’s suffers the usual issues with regards to adapters and flange focal distances. That said, the C/Y mount has 1,5 mm of FFD leeway on the Canon EF mount, and that is enough for a dumb adapter to enable the combination without issue. Furthermore, there are specialist companies which have offered conversion kits for converting some of the most desired C/Y mount lenses to select other mounts (e.g. here).

With mILC’s, the use of C/Y lenses is a breeze. There are dumb adapters available which – for a pittance – allow you to mount all your C/Y -lenses on your mirrorless of choice. Again, if your mILC is of the full-frame variety, the C/Y -lenses will work exactly as designed, and if your mILC has a smaller-than full-frame sensor, you can choose to either use your C/Y lens with a crop factor, or invest in a focal reducer in order to circumvent the crop factor.

One final note: Especially Zeiss lenses for the C/Y mount originally came in two varieties: AE and MM. While not meaningless (some internal changes to diaphragm and optics were made), the distinction is far from crucial when using the lenses with an adapter. More on this (and many other details) one day in that article which is yet to come.


To be added later, sorry.
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To be added later, sorry.
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Introduced as early as 1936, the Exakta (sometimes also spelled Exacta, subsequently referred to as EXA) bayonet mount is one of the earliest and most influential interchangeable lens camera mounts. Let’s start with identifying it:

Carl Zeiss Jena Biotar 1:2 5.8 cm

Identifying the mount
For a bayonet mount, the EXA-mount is exceedingly simple:
[1] Three-pronged bayonet with three identical prongs, spaced 120 degrees apart
[2] Locking pin at 3:30 o’clock.
– Like many older mounts, the EXA-mount is relatively small. The inner diameter of the mount is merely 32,5 mm, and the outer diameter (prongs included is 37,5 mm). This makes the mount actually narrower that the M39 rangefinder mount and places a significant limitation on the size of a lens’ rearmost optic.
– One often encounters EXA lenses which have a pod-like construction attached to the side of the lens (see pic below). That pod acts as a pass-through for pressing the shutter on the camera body, while also activating the lens’ aperture stop-down mechanism. You press the button at the end of the pod, it stops down the lens and triggers the shutter button on the body. While lenses which have those pods are very simple to identify, these pods are not an absolute requirement for EXA lenses.
– The EXA-mount was originally just based on the internal bayonet (shown above), but later versions introduced an external bayonet as well, intended for the more secure fastening of long, heavy lenses. See more here.
– The EXA-mount started out with only a bayonet and locking mechanism, and no way to transfer information to or from the camera. As with the M42-mount various fixes and extra features were added at later stages. Hence, your lens’ mount may show features not visible in this picture. Resultingly, there are some incompatibilities between various EXA cameras and lenses. Those I will not cover here, partially because (with the right adapter) few of those extra features obstruct the use of the lens as adapted (and these features are anyhow not useful when using the lens on an adapter).

Obiettivo fotografico grandangolare - Museo scienza tecnologia Milano 09789
ISCO Westrogon 24 mm f/4
Photo by Museo della Scienza e della Tecnologia “Leonardo da Vinci” shared on Wikimedia commons (CC BY-SA 4.0)

General information on the EXA mount.
The EXA-mount has its origins in the Ihagee Kine Exakta of 1936 – a camera which in many ways paved the way for the modern concept of an SLR and is widely credited for having been the first 35 mm SLR. While the Kine Exakta was an instant hit, manufacture of the camera seized in 1940 because of the war. After the war Ihagee – the manufacturer of the Exakta – met a fate very much like that of Zeiss, meaning that there was an Ihagee both in East and West Germany, and both wanted to use the name.

Even though the war was a major spanner in the Ihagee works, and even though after the war the main manufacturer of Ihagee cameras (Ihagee East) was locked up behind the iron curtain, the Ihagee Exakta and Exa lines of cameras were a huge hit in the late 40’s and 50’s. Not only were they technlogically very advanced, but also partially aided by their iconic shape, and high media profile (e.g. featuring prominently in Hitchcock’s Rear Window). As a result of the popularity of the body, EXA lenses were manufactured in the thousands (not thousands of lenses, but thousands of different lens models).

Aside from the two Ihagee’s (East and West), the Exakta lens mount was also taken up my other camera manufacturers. Most prominent of these was Topcon (originally Tokyo Kogaku Kikai Kabushiki-Kaisha). Topcon’s first, and highly acclaimed line of SLR’s used the EXA bayonet for attaching lenses (leading to that the mount is sometimes referred to as the Exakta/Topcon mount. Also, the mount was briefly used by Mamiya for a line of SLR’s which were mostly sold as rebrands (among others as ‘Sears’) as well as a trio of relatively obscure camera manufacturers (Tokiwa Seiki, Corfield, and ELOP).

The attractiveness of the EXA mount for those who want to dabble with old lenses lies on two fronts: Firstly, as EXA-mount lenses go as far back as the pre-war era, and had their heyday before the advent of the Japanese SLR, EXA-mount lenses open a window into a time when Germany (pre-war as well as East and West) were the undisputed kings of cameras and optics. As a result of this, Exakta is one of the go-to -mounts (the other being M42) for lenses by as diverse a range of manufacturers as Carl Zeiss Jena to Rodenstock; Meyer-Optik to Schneider as well as many less well known manufacturers such as Enna, ISCO, Kilfitt, Piesker, Schacht, Steinheil. Furthermore, several Japanese manufacturers also offered lenses for the EXA mount, among them household names such as Canon, Nikon, and Olympus, as well as some less well known brands. In spite of the limitations defined by the size of the mount, the EXA-mount even for some time carried the fastest production lens of its time – the fabled Taika Harigon 58/1.2

The second attraction is that as EXA lenses have traditionally been less easily adapted, partially due to the convolution inherent in the way the mount evolved. Thus many classic lenses (like the Zeiss Biotar shown above) which are available in both M42 and EXA mounts, can regularly be had more cheaply in EXA-versions.

Adapting EXA-lenses
I’m sorry, as this is a somewhat messy topic, and as I have not been able to obtain and test all the myriad EXA-mount variants, you should take this with a pinch of salt. Also, I will not in any way address the adapting of EXA lenses for dSLR’s, although I assume that for some combinations of lens and body it should be workable. The basic rule, if you’re not sure if a specific EXA lens will fit a specific adapter, is ask. Ask google, ask on a vintage/legacy lens forum. Ask, until you feel confident.

On mirrorless bodies, adapting EXA lenses should pose no extreme difficulties, assuming that the adapter is correct. The adapter I am currently using is only fitted for using the internal EXA bayonet, but there are also adapters for most mirrorless formats which also offer an external bayonet. Also, considering all the contraptions various manufacturers (most prominently, Topcon) added for lens-body communication, there is always a risk that those contraptions may interfere with an adapter not designed to take those demands into account. Again: ask.

Four thirds

To be added later, sorry.
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Fujica X

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Fujifilm X

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Icarex BM

Carl Zeiss Skoparex 35 mm f/3.4

Key characteristics of the mount of Icarex BM lenses:
[1] Breech-lock ring with two, openings of different sizes
[2] Breech-lock registration pin (always aligned with lens top)
[3] Aperture stop-down pin
[4] Thingamajig (I have no idea what this is for. If someone knows, please enligten me)
Note! The rear of Icarex BM lenses typically (based on four lenses) have very prominent slot-screw heads, but their number and spacing is not a definite characteristic.

Basics of the Icarex BM mount:
The Icarex “bayonet” was introduced in tandem with the Zeiss Ikon Icarex35 camera in 1966. The story of the Icarex camera and “bayonet” is a sordid tale of how – in some rare cases – companies manage to do everything wrong. In short:
• Zeiss Ikon was worried about the Icarex eating into sales of their other products (Contarex and Contaflex). Hence, the Icarex was crippled and (in many ways) obsolete at launch.
• Only three lenses were offered for the Icarex at launch, and two of those were different 50/2.8’s (a four element ‘Tessar’ and a three element ‘Pantar’). It took another two years before Zeiss Ikon launched anything wider than 50 mm and anything narrower than 90 mm.
• The Icarex was initially launched without any built-in metering, even though the major competition offered integrated metering (and was able to sell well due to this). Integrated metering capability was added to the Icarex only in 1969.
• Through launching the Icarex, Zeiss Ikon added one more mount to support. This was partially due to that …
• The Icarex was not really a Zeiss Ikon design. Instead it was a rehashed Voigtländer design (Zeiss Ikon had acquired Voigtländer earlier). This probably contributed to Zeiss Ikon’s lacklustre effort in pushing the Icarex.
• Almost of all lenses manufactured in Icarex BM mount (under the ‘Carl Zeiss’ brand were actually rebadged Voigtländer lenses. Even the BM mount 50/2.8 “Tessar” was actually a Voigtländer Skopar. As such this is not a bad thing (Voigtländer was an optics pioneer), but shows how the Icarex was destined to be the unwanted stepchild.
• As sales were disappointing, Zeiss Ikon launched a parallel series of Icarex cameras with m42 thread mounts in 1969. Subsequently, Icarex cameras would be either “TM” (m42) or “BM” (Icarex). (Any Icarex cameras without a “TM” badge are “bayonet” mounted)
• To add insult to injury, the Icarex “bayonet” mount is actually a breech-lock mount (which is why I’ve parenthesized “bayonet”).

As such, this sorry story is indicative of the miserable end-game of the (west) German camera industry. While many like to portray this tale simply as a “could not compete against cheaper asian labour” -story, it is actually a story of arrogance, incompetence, infighting, and chronic indecision. Maybe I’ll tell my take (the management scholar’s version) one day.

In any case, all this resulted in that the Icarex BM mount was officially discontinued in 1971, after only 5 years. Luckily, and thanks to the relatively massive flange focal distance of the Icarex BM mount (48 mm), owners of Icarex BM lenses were able to adapt their lenses to a wide repertoire of cameras. Furthermore, Icarex cameras turned out to be sturdy and serviceable.

Adapting Icarex BM lenses:
Obviously, thanks to the relatively forgiving flange focal distance of Icarex BM lenses, there are few theoretical or practical impediments to adapting these lenses – both to dSLR’s and mirrorless cameras. On the other hand, due to the relatively meagre installed base of these lenses, third party adapter manufacturers have not been too eager. Resultingly, while adapters exist, only some mounts are covered. Furthermore, dedicated Icarex BM speed boosters (for owners of APS-C bodies) do not exist. Hence, should one want to speed boost an Icarex BM lens, one needs to find a suitable combination of adapter ring and speed booster.

Once an adapter has been acquired, the use of Icarex BM lenses on MILC is very straightforward. Furthermore, the 10 Icarex BM lenses manufactured by Zeiss/Voigtländer are of the highest build quality, and while usability-wise some of them may be considered somewhat quirky (even medium tele lenses like the 200/4 Dynarex have a very narrow focus ring), their build quality is second to none. Furthermore, Zeiss/Voigtländer Icarex BM lenses are devoid of click-stops (which especially some will appreciate).

Also other manufacturers (some of the customary third party manufacturers) offered lenses for the Icarex BM mount, but these are relatively rare.

P.S. One cannot really have a discussion about Icarex, without mentioning the “Carl Zeiss Ultron 50/1.8” lens (which, BTW, also was a Voigtländer design). Few lenses in this focal length and speed have an equally fearsome and fabled reputation, and I know of many who have acquired an Icarex BM adapter simply to be able to use their Ultrons.

Konica AR

Konica Hexanon AR 35 mm f/2.8

Key characteristics of the mount of Konica AR lenses:
[1] Locking notch at 9 o’clock.
[2] Three bayonet prongs, all tapered on all sides.
[3] Combined stop-down lever and aperture indicator (moves with aperture ring).

Basics of the Konica AR mount:
If you’re new to photography, the name Konica might not register. Otherwise, you will certainly not need to be told of the Konica’s once stellar reputation or of the many ground-breaking innovations Konica was first to introduce. The Konica AR mount is a relatively long-lived (1967-1987) lens mount for Konica SLR cameras. The Konica AR mount replaced the preceding (and more short-lived) Konica F mount. The Konica AR and F mounts are not in any way compatible, even though the AR mount initially inherited a lot of the Konica F mount’s lenses.

Interestingly, Konica was relatively prescient in its 1960’s design of the AR mount, as its interface was able to cater to all the needs (such as shutter-priority or program auto) of the next two decades in stride. While many Konica lenses went through several modifications and improvements throughout their lifespan, the Konica AR mount remained unchanged for its entire existence.

The sad fact is, that due to reasons largely unrelated to the quality of its lenses, Konica was one of those otherwise venerable makers of manual focus cameras, which did not manage the transition to autofocus. To my knowledge, Konica never even tried to market an autofocus SLR. Thus, the Konica AR mount remained Konica’s last lens mount. Konica stayed in the camera business, making viewfinder/compact cameras and even a rangefinder of some repute, and only re-entered (after a fashion) the SLR business in 2003, through a merger with Minolta. In some minor form, Konica lives on in the form of Sony (which took over from KonicaMinolta in 2006).

While the Konica AR mount was never very popular among third-party lens makers, and although Konica did not churn out as many different lenses for its mount as e.g. Canon did (during largely the same period), the Konica AR mount nevertheless sports a full range of lenses, especially among fixed focal length lenses (primes). Also, while Konica did not emphasise zooms as much as some competitors did, the mount sported a number of both consumer and pro zooms in all the typical focal length ranges (for that period). Also, many appreciate the fact that Konica held on to metal lens construction long after most rivals had gone into plastics (in the final days, some Konica-branded plastic lenses were introduced, but these were short-lived and quite rare). Konica lenses – even the later ones which did utilise plastic or rubber, are typically sturdy, reliable constructions.

Adapting Konica AR lenses:
Konica AR lenses are fully manual lenses, and both focus and aperture are controlled by dedicated rings. Thus Konica AR lenses function perfectly on any full-frame mILC, using a cheap dumb adapter.

With mILC’s using smaller-than full-frame sensors, Konica AR lenses can be more of a mixed bag, as no focal reducers for Konica AR lenses are currently available. Many of Konica’s moderate wide, standard and short telephoto primes are perfect candidates for use on APS-C mILC’s without focal reducer, but genuine wide-angle performance remains a sore point on APS-C (and smaller) mILC’s.

The few genuine (albeit, minor) ‘gripes’ that many have regarding using adapted Konica AR lenses, are both related to the function of the aperture ring (and affected original Konica Film SLR users similarly): Firstly, the ring ‘clicks’ are usually quite pronounced (making moving the aperture ring less smooth as, say with Canon FD lenses), thus making de-clicking a Konica AR lens a tempting proposition also for still photographers. Secondly, alike many lenses of its era, Konica AR lenses supported giving the camera body control of the aperture, which was done through twisting the aperture ring past the smallest aperture, into a range indicated as EE or AE (depending on the era of the lens). Problematically, you can enter this range accidentally (assuming you are not in tune with your lens), and once you’ve reached EE/AE, the aperture ring locks and you need to decisively depress a button to regain normal operation of your Konica AR lens aperture ring.

Compared to e.g. Canon FD lenses (which also had an auto-lock setting on their aperture rings), the main difference (and point in Konica’s disfavour) is that with Konica AR lenses, you can accidentally lock the aperture ring simply by twisting it past max aperture, whereas with FD lenses, you had to depress the auto-lock button both to enter and exit auto-lock mode.

Konica Hexanon AR 135 mm f/3.5
[1] Once aperture ring is turned to AE (or EE on older lenses) position, the aperture ring locks at minimum aperture.
[2] Button, depressing of which releases aperture ring to allow normal movement.

The Konica AR mount is special in that it – of all 36×24 mm (‘full-frame’) reflex cameras – has the shortest flange focal distance (40,5 mm). Historically, this has seriously hampered the attractiveness of Konica AR lenses, as – prior to the advent of full-frame mILC’s the only way to use a Konica AR lens as intended, has been to use it on a Konica Film Camera (production of which ceased in 1987). Resultingly, prices for Konica AR lenses was seriously under-representative of their quality for a long time, and have only recently returned to represent their photographic potential. While this warms the hear of any real Konica fan, it is less welcome news for those collectors, hoarders and other sufferers of gear acquisition syndrome who do not yet have all the Konica lenses they’d want.

Konica F

To be added later, sorry.
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Leica L

To be added later, sorry.
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Leica M

To be added later, sorry.
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Leica R

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Leica thread mount (a.k.a Leica screw mount, LTM, L39)

If M42 is the quintessential general thread mount for SLR’s, the Leica thread mount is the original thread mount for rangefinder cameras. While the LTM mount has its origins in 1914, what we today know as the LTM was de-facto standardised in 1931. Ancient history to most of us, but still relevant today.

The standard LTM mount has an outside diameter of 39 mm, a thread pitch of 26 turns per inch ( roughly 0.98/mm) and a 28,8 mm flange focal distance. The somewhat oddball thread pitch is based on Leica’s previous work with microscopes, and is one of the curiosities of what in essence is a century of photographic legacy.

While the LTM was used by Leica only until 1954 (after which Leica cameras use the Leica M-mount), a major part of the reason for the range of lenses available for the LTM is that the pre-war Leica III was copied (one should say, reverse-engineered) by many other manufacturers including Canon, FED and Zorki, and most of these were manufactured long after Leica had themselves stopped manufacturing LTM cameras and lenses.

Left: Jupiter-8 (50 mm f/2); Right: Voigtländer Super-Wide Heliar 15 mm f/4.5 Aspherical.

LTM lenses are simple thread mount lenses, with no communication between lens and body. While the shortish flange focal distance makes them largely unattractive for adapting on SLR’s, LTM lenses have long been adapted to Leica M bodies. Interestingly, the fact that LTM lenses have been easily adapted to Leica M -bodies has kept the LTM mount attractive as third-party lens manufacturers have been able to reach a wider audience by manufacturing LTM lenses for use on either LTM or Leica M bodies.

With the advent of mirrorless digital cameras, a new world has been opened up for these lenses. Given the generally diminutive size of typical LTM lenses, these lenses are attractive to all those photographers who want to couple their smaller bodies with smaller lenses (especially as modern lenses tend to keep growing). On the other hand, LTM lenses are often so small that they can easily be dwarfed by the bodies they are mounted on.

Voigtländer 15/4.5 on Sony a7R (with vertical grip). Even with the adapter, the lens is diminutive.

That said, there are some things one should be aware of when mounting rangefinder lenses on modern mILC’s. Due to a combination of the short flange focal distance, how some lenses (especially ultra-wide angle lenses) tend to protrude into the lens mount, and the properties of digital sensors, many rangefinder lenses do not deliver as good results on mILC bodies as those film cameras they were originally designed for (something I touch upon here).


As noted, the M42 is the quintessential general thread mount, and M42 lenses have been manufactured by a plethora of manufacturers (and sold under even more names). Moreover, the M42 mount is relatively easy to positively identify by the unique combination of thread diameter (42 mm) and thread pitch (1.0 mm).

That said, within the M42 mount, there are a number of variations which users should be aware of (even though they have a very limited impact on the adaptability of said lenses). The following pictures will illustrate these variations. (N.B! I am aware of some rare variations, which I have yet been unable to find sufficient documentation for, and are thus not covered.)

M42 lenses with direct aperture coupling

At its simplest, M42 lenses have no other controls than two rings: one for focusing, and another for setting the aperture. Such lenses in no way communicate with the camera body – neither do they transmit the selected aperture to the body, nor can the body control the aperture.

Historically, the downside of using such lenses was that one would either have to focus and compose the picture wide open and then remember to stop down to gain adequate depth-of-field (or short enough shutter time) or contend with trying to peer through a very dim viewfinder. Later preset and auto -lenses addressed this problem, but there are M42 lenses – typically either very old or very cheap – which function according to this principle. For an example, see picture below.

Feinmess Dresden Bonotar 105 mm f/4.5 (10 aperture blades)
The upper ring operates the aperture directly, and the M42 mount is just a thin tube of aluminum with threads. The aperture ring does not have clicks, and the “stops” are not evenly spaced.
M42 ‘Preset’ lenses

Preset lenses were a further development of directly coupled lenses, designed to address the central usability issue stemming from that focusing (and composing) was best done with a wide-open aperture, whereas shutter timings and requirements regarding depth-of-field often necessitated shooting stopped down.

Preset lenses typically have dual aperture rings: the actual aperture ring which works based on direct coupling (and typically has no clicks), and the preset ring, which would be used to limit the upper (low f-stop) end of the aperture ring’s movement. As there are multiple user interface arrangements of preset lenses, see pictures and captions below.

Helios M44-2 (58 mm f/2) preset lens (M42)
The topmost ring (with numbered stops) is the preset ring, and it has clicks. The actual aperture ring is the ribbed ring below, with a small red dot indicating the actual aperture (f/2.8)
Tokyo Koki (Tele-Tokina) 135 mm f/2.8. (15 aperture blades)
The topmost ring is (again) the preset ring, currently allowing full (f/2.8–f/16) movement of the aperture. The actual aperture ring is the one below, currently set to f/4. Note that both rings are numbered.
Meyer-Optik Orestor 135 mm f/2.8 (Zebra, 15 aperture blades).
This lens can easily be mistaken for a direct-coupling lens, because the preset ring is not obvious. Note the red triangle below ‘5.6’, which indicates the current aperture, and the red dot above ’32’ which indicates the upper end of the aperture range. The preset-action of this lens is activated by pushing the entire aperture ring forward and turning it to a new setting.

The way in which preset lenses were used on film cameras would be that the photographer would first set the intended aperture (based either on metering or rules-of-thumb) on the preset ring, then turn the aperture to fully open, compose-and-focus, and could then – without taking the camera from their eye – twist the aperture ring to the preset, and take the shot.

From the viewpoint of the photographer using their lens on a modern digital camera, this all might seem archaic, but preset lenses have some advantages even today. Firstly, as all (that I know of) preset lenses are without aperture clicks, they lend themselves both to videography and in-between-stops shooting. Secondly, as the aperture mechanism of preset lenses was always operated by a human hand, and not a spring, the aperture mechanism did not need to move as lightly as that of all automatic lenses invariably have to. Thus, many preset lenses have (from today’s viewpoint) insane numbers of aperture blades (with all the advantages that entails), and are not bothered by small amounts of oil on the aperture blades.

N.B! Preset lenses are not limited to the M42 mount, but are a general trait of pre-auto lenses. For example, the Tokyo Koki lens pictured above, is actually a T-thread lens. That said, they are a significant piece of the M42 lineage and are therefore treated here.

M42 ‘Auto’ lenses
Chinon 55 mm f/1.7 (M42)

The picture above shows the M42 mount in its most typical form: an ‘auto’ lens.
[1] 42 mm thread (with 1.0 mm thread pitch]
[2] pin for stopping down lens to pre-set aperture (used in automatic mode).
[3] switch for selecting between auto(matic) and manual aperture mode.

(NOTE! While the most typical implementation of the camera-driven stop-down mechanism is a simple pin, there are some other arrangements as well)

The idea with these ‘auto’ lenses was to (when set to auto) allow composition and focusing with a fully open aperture, and automatic stopping down for taking the picture (a lever in the camera body would depress the pin [2] before taking the shot. Metering would depend on ‘stop-down -metering’, meaning that to meter, the camera user would depress a button or lever on the camera body, which would depress the pin in the lens, stopping it down, whereafter the photographer would be able to see in their viewfinder, how suitable the exposure was.

While the most common approach to auto lenses was to use an auto/manual switch to allow the user to switch between modes, there are also variations. Some ‘auto’ M42 lenses were – for all intents and purposes – auto-only, such as the Meyer Optik Domiplan 50/2.8 pictured below. Others lacked an auto/manual switch, but had an arrangement for stopping down the lens irrespective of the camera body, such as the Meyer-Optik Orestegon 29/2.8 (also pictured below). While such lenses are as such just as good as other lenses, they pose a distinct problem for people wanting to adapt them, as the lens either needs to be modified, or the stop-down -pin needs to be jury-rigged to be depressed all the time in order to allow any stopping down of the lens.

Left: Meyer-Optik Domiplan 50 mm f/2.8 (auto-only)
Right: Meyer-Optik Orestegon 29 mm f/2.8 (auto-only with stop-down button on lens).
M42 lenses with two-way communication

Two-way communication implies that not only does the body tell the lens when to stop down, but that also the lens has some way of communicating the selected aperture. In this category, there are two types of implementations: mechanical (pioneered by Asahi/Pentax) and electronic (pioneered by Pentacon/Praktica).

SMC Takumar 55 mm f/1.8

The mechanical approach to two-way communication still utilised the M42 thread mount [1] and still had the same stop-down pin [2] as earlier implementations. The central addition was the aperture linkage pin [3], which was directly coupled to the aperture ring, thus allowing the body to read the selected aperture. There was a further pin [4] which needed to be depressed to enable activating the auto-setting on the auto/manual selector [5]. (See also Gerjan van Oosten’s comment below)

Pentacon electric 135 mm f/2.8

The electronic approach naturally retained the M42 thread-mount [6] and stop-down pin [7] and auto/manual switch [9] for backward compatibility, but was otherwise based on three (spring-loaded) electronic contacts on the lens’ mount flange [8], which would communicate with similar contacts on the mount flange on (compatible) camera bodies in order to communicate the lens’ selected aperture. When introduced in 1969, this was the first-ever implementation of electronic communication between lens and camera. The M42 being a thread mount, and with perfect alignment thus being somewhat unreliable, this led to the use of wide tolerances on the camera body’s end of the electronic contacts.

Praktica LLC and Pancolar 50 mm f/1.8 lens with electronic contacts visible on lens and body.
Photograph by Dnalor_01 on wikimedia commons. Original.
Adapting M42 lenses

M42 lenses have been adapted to other mounts for about as long as other mounts have existed, partially due to that the M42 mount preceded many other mounts and people tended to already have M42 lenses when they bought their first Minolta/Canon/etc., partially because the M42 mount features many classic lenses. That said, there are huge practical differences in whether you adapt M42 lenses to SLR’s (whether film or digital) or mILC’s.

Adapting M42 lenses on SLR’s
There are two major considerations you need to consider when adapting M42 lenses on SLR’s. The first is the age-old question of compatible flange focal distances (adapting M42 lenses is easy as long as the camera body’s flange focal distance is comfortably short of the flange focal distance of M42 (45,46 mm), which means that many SLR bodies will able to fit an M42 lens and adapter ring without losing infinity focus. On the other hand, there are those systems (Nikon F, Leica R, Olympus OM, C/Y, others), which have longer flange focal distances than the M42 mount, and will thus either lead to losing infinity focus, or necessitating an adapter with optics, and the ensuing image degradation and mild teleconversion.

The other major consideration is metering, as (practically) no bodies of other systems will integrate the M42 lens to the camera body’s metering system, in effect forcing you to resort to stop-down metering, meaning that the photographer is suddenly back where M42 started: forced to either peer through dim viewfinder or to focus and compose wide open, then stop down to take the shot*. Neither of these considerations need affect the user of a mirrorless camera.

* granted, this issue can be circumvented using live view on modern dSLR’s.

Adapting M42 lenses on mILC’s

Firstly, the question of flange focal distances becomes a non-issue, as there is no mirrorless interchangeable lens camera (not even medium format mirrorless), which cannot comfortably fit a M42 lens and adapter.

Secondly, as mirrorless cameras focus and meter on sensor (not using a complicated set of mirrors and prisms), both metering and focusing M42 lenses becomes essentially child’s play, with one small potential hitch: the lens needs to be in manual mode for the aperture to work.

With (most) adapters not being designed to be able to depress the stop-down pin of M42 lenses, auto-only lenses can only be used wide open (or through jury-rigging the stop-down pin). Similarly, I could tell several tales of shots I’ve botched because I’ve accidentally switched my M42 lens into auto mode (meaning all shots have been made with the aperture wide open. If your shooting habits are as uncontrolled as mine, you might want to consider taping the auto/manual switch solidly to manual.

Micro four thirds

To be added later, sorry.
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Minolta A

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Minolta SR (and MC and MD, and X-600)

The Minolta SR mount was introduced in 1958, together with the Minolta SR-2 SLR, making it one of the earliest bayonet mounts for an SLR camera. Like many of the lens mounts of the era (60’s–80’s), it went through several iterations during its existence, gradually incorporating new features. Here we will briefly identify these iterations:

Minolta MD 45 mm f/2

Key characteristics of the mount of Minolta SR/MC/MD lenses:
[1] Three-pronged bayonet mount, with locking notch at roughly 6:30 o’clock. (SR, MC, and MD)
[2]Aperture stop-down lever (moves with aperture ring, but is not used (?) for metering). (SR, MC, and MD)
[3] Lens-internal and not part of interface. Disregard. (visible on some lenses)
[4] Meter coupling (MC) ridge, interfaces with pin on camera to report selected aperture, used for metering. (MC and MD)
[5] Minimum aperture ridge, interfaces with pin on camera and reports lens’ minimum aperture, used for metering in shutter priority and program modes. (MD only)

Other variants:
Firstly, while the picture above shows three (of six) bayonet prongs to be tapered, this varies in practice. Many Minolta lenses also tapered the edge indicated with 1b, while I’ve seen third-party SR/MC/MD lenses, which had all edges tapered.
Secondly, the aperture stop-down lever is not a must. Both Minolta and third-party manufacturers offered lenses for the SR-mount which did not have an automatic aperture (mostly preset lenses, see also section on preset lenses under M42-mount). For an example, see picture below.
Thirdly, the X-600 lenses are MD-lenses with an extra prong readable by the Minolta X-600 body. See picture below.

Left: Tokyo Koki Tele Tokina 135 mm f/2.8 Preset lens, without aperture stop-down lever.
Right: Minolta MD 135 mm f3.5, with X-600 indicator prong (at about 9:45). Note that the position of the X-600 indicator prong depends on whether the lens maximum aperture is f/2.8 or brighter.

Historically, these elements of the lens’ interface were intended to co-operate with their counter-elements on the body. Due to the manner in which Minolta implemented the variations, forward- and backward compatibility was almost total: An MD-enabled body could use an SR lens as well as an SR-era body could have, while MD lenses could be mounted on MC-and SR -age bodies without issues. Considering the manner in which some of Minolta’s competitors stumbled with retaining compatibility, this is no small feat.

Upper and lower half of lens mount on a Minolta SRT-101b.
[6] Locking pin which interfaces with locking notch.
[7] Lens release button (push down to release locking pin)
[8] Meter coupling pin. Interfaces with MC ridge on lens. (MD pin not in picture, as no MD-enabled body on hand.)
[9] aperture stop-down lever, activated both by shutter and depth-of-field preview button.

History of the SR (MC, D, X-600) mount
From the relative obscurity of Chiyoda Kogaku in 1958, Minolta SR mount cameras and lenses raised the company to the forefront of 35 mm photography in less than three decades. When Minolta (in 1985) introduced the world’s first functional body-driven autofocus system, few pundits were really that surprised that Minolta beat its competition to the punch. The dedication, ingenuity and workmanship displayed by Minolta in these three decades were admired widely – not only by the millions of customers, but also by several competitors (most notably, Leica. See more here and here, or in the December 2011 issue of Amateur Photographer).

Among the SR/MC/MD line of lenses and bodies, there are many notables (too many to mention, but maybe worth a separate article one day). Suffice it to say, that you do not need to be a Minolta fanboy to appreciate the gear.

But, Minolta’s reaching for new heights with the launch of its line of autofocus cameras and lenses was the undoing of the SR lens mount. Alike some of its fiercest rivals, Minolta decided to pursue autofocus based on an entirely new lens mount. Moreover, due to the difference in flange focal distance between the Minolta SR mount (43,5 mm) and its successor, the Minolta A-mount (44,5 mm), SR-mount lenses could not be adapted to the new bodies as manual focus lenses without either losing infinity focus or having to use an adapter with optics. Those Minolta SR users who had a sizeable investment in SR/MC/MD lenses were left high-and-dry. To say that Minolta’s move lost them a lot of goodwill, would be a sizeable understatement.

Then again, there is little reason to suspect this to have had a significant influence on Minolta’s ultimate demise two decades later, as Canon did precisely the same (orphaned it’s FD-users) when shifting to a new autofocus mount and managed to come out on top (although the transition was not smooth).

Adapting Minolta SR/MC/MD lenses
Yes please, thank you very much. Or maybe not. It depends.

The first is definitely true on mirrorless Interchangeable Lens Cameras. Due to their fully-manual nature, Minolta SR lenses – of every variant – function beautifully (but manually) on mirrorless cameras. Having been designed for 35 mm film, the combination is – naturally – at its smoothest on full-frame mILC’s, but even with APS-C and MFT mILC’s the marriage is not necessarily problematic: You either gain some ‘zoom’ (crop factor) or employ a focal reducer. Compared to e.g. Konica AR lenses, the availability of focal reducers for Minolta SR lenses is a big plus. Moreover, there are several accounts (here and here and otherwhere) pointing to that a decent number of Minolta SR lenses actually have image circles big enough to manage to cover the sensor of digital medium format cameras.

On dSLR’s the second (maybe not) is sadly true. With a relatively short flange focal distance (43,5 mm) the Minolta SR mount does not lend itself well to adapting on dSLR’s. In fact, the only dSLR with a shorter flange focal length than that is the (no longer manufactured) Olympus four thirds system, but that still means incurring a significant (potentially unwanted) crop factor. Otherwise, the alternative of using an adapter with optics remains, but is far from perfect.

Miranda bayonet

To be added later, sorry.
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In the meantime, see the pages of the Miranda Historical Society

Nikon F

The Nikon F-mount has been in continuous use since 1959, and has – unavoidably – progressed a bit since then. Due to the existence of an article dedicated to the Nikon F-mount, issues regarding generalities or adaptability of Nikon F lenses will not be discussed here. Instead, only aspects regarding identification will be addressed.

The Nikon F-mount has gone through four visually distinguishable iterations: Pre-AI; AI & AI-s; AF(D); and AF-S/P.


[1] locking groove at 3 o’clock
[2] aperture release lever
[3] “Rabbit ears” for communicating selected aperture to camera body.
Note: the fact that the rabbit ears are at 6 o’clock in this (these) picture is coincidental, as the position of the rabbit ears change according to the selected aperture.
(Pictured: K Nikkor 50mm f/2)
[4] Notice, that a ring (black) protrudes beyond the lens mount (chrome) all around the lens. This ring, is what makes (unmodified) Pre-AI lenses incompatible with most Nikon cameras post 1977.
[5] Bayonet prongs (for mounting on body)
(Pictured: K-Nikkor 50mm f/2)

AI and AI-s
First AI…

[6] Notice how the aperture ring (black) protruding beyond the actual mount (chrome) has been indented in several places? This is automatic indexing, and its functionality basically parrots that of the MC prong in Minolta MC and MD (SR) lenses.
(Pictured: AI Nikkor 50mm f/1.4)
[7] Duplicated aperture scale (viewable in viewfinder), another AI (AI-S and AF) trait.
(Pictured: AI Nikkor 50mm f/1.4)

Then AI-s…

[8] Most of the changes made from AI to AI-s were internal, but…
[9] This notch on the lens mount base shows that the lens is AI-s.
[10] Some AI-S lenses lost the rabbit ears, while others retained them.
(Pictured: Series E Nikon 50mm f/1.8)
[11] The AI-s notch from a different angle.
(Pictured: Series E Nikon 50mm f/1.8)

AF and AF-D
AF and AF-D lenses have identical mounts, and distinction has to be based on lens nameplate or serial number.

[12] Slot head for body-driven autofocus.
[13] (spring-loaded) Electronic contacts
[14] Rabbit ears gone (no AF lenses have them)
(Pictured: Nikkor AF-D 50mm f/1.4)
[13] (spring-loaded) Electronic contacts, other angle.
(Pictured: Nikkor AF-D 50mm f/1.4)

Significantly, modern Nikon F-lenses (those which have electronic contacts) differ from most other lenses with electronic contacts, in the placement of those contacts. While some mounts (M42 electric, Pentax K, Praktica B…) have electronic contacts on the lens mount flange, others have their contacts on the inside of the mount bayonet (e.g. Canon EF, Minolta/Sony A, MFT, etc.), pointing towards the sensor plane, Nikon’s arrangement of having contacts on the inside of the bayonet, pointing away from the optical axis is an obvious identification-trait.

AF-S and AF-P
AF-S and AF-P have identical mounts, and distinction has to be based on lens nameplate.

[15] Enlarged console for electronic contacts, and now with more contacts.
NOTE the absence of slot-drive screw, AI ridges and AI-s notch. The only things that remain, are the bayonet prongs, the locking groove and the aperture release lever (which itself is absent on new electronic diaphragm lenses)..
(Pictured Nikkor AF-S 50 mm f/1.4 G)

Nikon S

To be added later, sorry.
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Nikon Z

To be added later, sorry.
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Olympus OM

The Olympus OM-system (originally, M-system) was introduced in 1972, making it a relatively late addition to the family of Japanese SLR mounts. Then again, maybe that late entry allowed Olympus learn from its competitors’ mistakes, because not only was the OM-system highly successful, but also not a single change had to be made to the lens mount during the entire lifespan (1972–2002) of the system.

The Olympus OM-system is one of those seminal camera systems, which one day will get the separate article (on this site), which it surely deserves. For now, we’ll have a brief look at identifying OM mount lenses, a general overview of the OM-mount and a discussion on adapting OM lenses.

Identifying OM-system lenses:

Pictured: Olympus OM 50 mm f/1.4

[1] Three-pronged bayonet mount, with tapered prongs.
[2] Locking pin (hidden beneath prong, here) at 4:30 o’clock.
[3] Lens release button. Operates locking pin [2].
[4] Aperture stop-down button (for depth-of-field preview). Pressing of button moves lever [5].
[5] Aperture stop-down lever.
[6] Aperture indicator lever (moves with aperture ring)

NOTE! A striking characteristic of the OM-system are the two opposing buttons [3] and [4]. Sadly, this characteristic (while obvious) is not foolproof, as both some Olympus lenses as well as third party lenses have arrangements which outwardly differ somewhat. The only foolproof identifier is the locking pin hidden under the bayonet prong at 4:30.

The OM system – a brief, general description:
While Olympus admittedly left its entry into the SLR market quite late, Olympus was in no ways new to the photography business. Also, entering a somewhat established market allowed Olympus to define a profile and market segment for themselves.

It seems, that from the very beginning Olympus aimed for simplicity, aesthetics and compactness. Olympus camera bodies have always been on the svelte side, and Olympus’ lenses typically are among the smallest and lightest in their respective classes. The user interfaces (for both cameras and lenses) are well thought-out and elegant. Workmanship and materials are likewise of high quality (especially the lenses). Furthermore, the lenses look darn nice.

It also seems clear, that the OM system was not just a stab at entering the SLR-market. Olympus made a dedicated effort and seems to have had an ambitious product roadmap from the get-go. The roster of Olympus OM lenses is just as comprehensive as that of their main rivals, interspersed with some fantastic feats of optical engineering.

Given the popularity of the OM system, third-party manufacturers also offered their lenses for the OM system, but my totally unscientific, gut feeling is that they never reached a major market share. Considering the traits which attracted users to the OM system (simplicity, aesthetics, compactness) and how these typically were been less pronounced in third-party offerings, this is maybe not surprising.

On the whole, I’d characterise Olympus’ record in photo equipment as one of ups and downs. While Olympus was at the height of its trajectory in the late 70’s and 80’s, the age of autofocus film SLR’s was not kind to Olympus. Also, while (now, in the digital age) Olympus long seemed to be the odd-man out, it is evident that Olympus is slowly improving its position. Then again, Olympus seems to be intent on not going into full-frame digital photography, leading to that OM lenses – while popular objects for adaptation in many circles – are less than ideal for Olympus’ digital cameras.

Adapting Olympus OM lenses
While the Olympus OM system technically remained alive until 2002 as a system for manual focus aficionados, all real emphasis on development of the system ended in the late 80’s. With many former OM system users progressing to other systems in the 90’s and 00’s, a great number of OM lenses have been available for use on other systems.

Interestingly, and largely thanks to one of the longest flange focal distances in 35 mm SLR systems (46 mm, shorter only than Nikon F and Leica R), Olympus OM lenses have been relatively easily adaptable to other SLR systems (such as Canon EF and others).

Today, Olympus OM lenses can be adapted to almost all digital interchangeable lens cameras (SLR as well as mirrorless), with some limitations: Due to longer flange focal distance of Nikon dSLR’s, these can use OM lenses only together with an adapter with optics; due to the unavailability of Full-frame sensors, some mILC’s (especially four thirds and micro four thirds systems) can use OM lenses either only with a significant crop factor, or in with a focal reducer.

Most importantly though, once adapted, the central controls of OM lenses (focus ring, aperture ring) work flawlessly. Out of my personal experience: OM lenses are a joy to use on a Sony full-frame mirrorless, and I see no reason why this should not apply equally to other full-frame mirrorless bodies as well.

Olympus F (pen)

To be added later, sorry.
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Pentax 110

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Pentax K

First off, The Pentax K -mount is probably the one bayonet mount with the greatest number of variations (8). Secondly, I am sad to admit I do not personally have examples of even half of the variations. Therefore, I’ll here give a short description of the mount (those parts which have stayed throughout all variations), after which I am sad to have to refer readers to an outside source for final confirmation.

Luckily, there is a well-written and (probably) highly comprehensive article on the variations of the Pentax K mount on the Pentax Forums site. Caveat: when you read that article, keep in mind that (unlike this site), that article shows lens mount pictures with the lens “upside” at 12 o’clock (not at 6 o’clock)

Pictured: Pentax-A 50 mm f/2

Key characteristics of the mount of Pentax K -lenses:
[1] Locking groove at roughly 9:45 o’clock – (ALL variations)
[2] Three-pronged bayonet mount, 4 edges tapered (two straight) – (ALL variations)
[3] Stop-down lever – (All variations but KAF4)
[4] Aperture indicator lever – (All variations)
[5] Electronic contacts at 1:30 to 2:30 (number varies) (All variations but K).

NOTE! Further:
– several variations (KAF, KAF2) include a slot-drive screw at roughly 1:30 o’clock
– likewise, several variations (KAF2, KAF3, and KAF4) include two power contacts for powering internal AF motors at 1 o’clock.

General comments on the Pentax K -mount:
If you are new to photography, it might surprise you, that Pentax has undoubtedly been one of the central players in the industry since the Japanese reconstruction post WWII. Likewise, throughout its history, Pentax has been a very innovative company, always among the first to stretch the boundaries of (what was assumed to be) possible.

In contrast to many other major Japanese manufacturers (Canon, Minolta, Nikon, Olympus) Pentax started its SLR production using the M42 lens mount, and abandoned it for its own bayonet mount (the Pentax K mount) as late as 1975. Further, in contrast to most (all but Nikon) of its competitors, Pentax also did not orphan its existing user base when moving forward into auto-focus cameras and lenses, instead opting to add autofocus functionality to its existing lens mount (while also keeping full forward- and backward compatibility). The general rule of the Pentax K mount is “you can always use older lenses on newer bodies”.

Not surprisingly, considering the multitude of demands placed on a lens mount over a span of almost half a century of active innovation, Pentax’s dedication to the K-mount has lead to some solution having been adopted, which clearly show their improvisational nature.

At the same time – counting by the number of lenses made for a mount – the Pentax K mount has been among the most popular in history. logs over one thousand different lenses made for the Pentax K mount – a number bested only by the Nikon F mount (and equalled by the M42 mount). What is striking in this number, is the relatively large share of third-party lenses.

The relatively large share of third party lenses as well as the large number of variations the Pentax K mount has endured, together conspire to making Pentax K-mount lenses a more-complex-than-normal challenge to attempts at identification. It is therefore with especial chagrin, that I admit my inability to offer my readers a conclusive identification guide.

Adapting Pentax K lenses:

… on dSLR’s:
As with Nikon F -lenses, legacy Pentax K -lenses are perfectly usable (actually more so than Nikon’s Pre-AI lenses) on any modern Pentax dSLR. With dSLR’s of other marques, the bane of flange-focal distances again comes to the fore, with basically only Canon EF bodies having a short enough flange focal distance to be able to use Pentax K -lenses without having to add image quality degrading optics to the adapters.

…on mILC’s:
The story is (again) very different and much rosier. Thanks to the large difference in flange focal distances between the Pentax K mount and (any) mILC mount, adapting to full-frame mILC’s is a breeze while small-frame mILC users may (again) use the adapted lenses either ‘as is’ or undo the crop factor using a focal reducer. But…
For a legacy lens to be useable as adapted on a mILC, there are two prerequisites: the aperture must be manually controllable and focusing must either be manually controllable or a smart adapter must be available. For older legacy lenses this is not an issue, but with Pentax K, this is a potential issue (as I have not yet been able to ascertain that a Pentax KAF4- compatible smart adapter exists), as some of the newer (KAF4) Pentax K lenses lack a manually controllable diaphragm and only focus-by-wire (meaning that no in-lens coupling between the focus ring and focusing mechanism exist).

Praktica B

The Praktica B (bayonet) mount may some day deserve an article of its own. Until then, we will discuss it here. We’ll start by identifying characteristics, thereafter briefly discussing general aspects of the mount, and the adapting of Praktica B-mount lenses.

Carl Zeiss Jena Prakticar 35 mm f/2.4 (Flektogon)

Key characteristics of the mount of Praktica B lenses:
[1] Locking groove at roughly 9:45 o’clock.
[2] Three-pronged bayonet mount, 5 edges tapered (one straight)
[3] Stop-down lever
[4] (spring-loaded) Electronic contacts at 1:30 to 2:30 (always just three).

The Praktica B-mount
Praktica (Pentacon) was originally one of the driving forces behind the M42 thread mount (in some markets its was referred to as the “Praktica thread mount”), and had taken an active role in trying to develop it further (see also section on the M42 mount). Pentacon also held on to the M42 mount long after most major camera manufacturers had deserted it in order to launch their own bayonet mounts. In the end (1978) also Pentacon admitted the inherent weakness of thread mounts, especially considering its limitations on camera-lens communication.

Interestingly, once Pentacon launched its own bayonet mount, it offered very few improvements over the capacities of the M42-electronic mount, that Pentacon had pioneered earlier. Even the electronic contacts had the same function (albeit spaced closer together). The two minor improvements were quicker, more secure mounting (inherent to bayonet mounts) and a quicker aperture stop-down (as long as the blades are dry and the spring is fully functional).

One can only speculate about the final fate of the Praktica B -mount, Pentacon, and the entire East German camera industry, as the reunification of Germany put an end to the production of Praktica cameras and led to a series of closures and re-amalgamations of East german optical companies. Would one indulge in speculation, one would have to consider the long decline of Praktica market share, and the relative slowness of east-bloc companies embracing novel concepts such as zoom lenses or electronics in cameras. Even so, there seen to have been some plans toward developing a high-end autofocus SLR, but whether those would ever had reached fruition (even without the GDR collapsing) is anyone’s guess.

So – you might ask – why care about the Praktica B mount at all? The answer is relatively simply, that the Praktica B -mount typically offers the most modern versions of classic East German designs (Flektogon, Pancolar, anyone?). Furthermore, while obviously some of the designs offered by Pentacon and Carl Zeiss Jena (e.g. Pentacon Prakticar 50/1.8) are quite pedestrian, they are by no means below-average (legacy) lenses. Thus, there is reason to have a lasting interest in the mount and its glassware.

Adapting Praktica B-mount lenses.
With the flange focal distance of the Praktica B mount being a relatively short 44,4 mm, adapting Praktica B-mount lenses has realistically only become feasible after the advent of mILC’s. As with most lenses originally designed for 35 mm film, they are ideally adapted on full-frame sensor cameras, exacerbated by that (currently) no focal reducers are available (or usable) for Praktica B-mount lenses. Once a suitable adapter has been purchased, their functionality is unproblematic, as they function totally manually.


To be added later, sorry.
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Rollei QBM

To be added later, sorry.
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Sigma SA

To be added later, sorry.
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To be added later, sorry.
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Topcon bayonet

To be added later, sorry.
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Zenit M39

To be added later, sorry.
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Medium format lens mounts

Descriptions of the following mounts may be added at a later date:

Fujifilm G

To be added later, sorry


To be added later, sorry

Pentacon Six

To be added later, sorry

Pentax 6×7

To be added later, sorry

Pentax 645

To be added later, sorry


  1. Nice work, very helpful. With the SMC TAKUMAR you left out one of the items. There is another pin, the square extension. It serves to compensate for small tolerances in the screw mount and for how loosely or tightly you screw the lens onto the camera. The whole aperture simulator is not fixed in the lens mount, but can rotate. The square extension serves as a kind of index to make sure the camera receives the correct aperture setting. Not all SMC lenses have light meter coupling pins and there are even Super-Takumar lenses that do have them.

    1. Thank you very much Gerjan. That’s what you get from not having a Pentax M42 camera on hand. I hope you don’t mind if I mention your name when I get to updating the text?

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