PLEASE NOTE! Two things:
First: This guide is far from complete, but I have made it public anyway, because even in its current state it can help many people.
Second: There have been several extensions of this article, and a version history is available.

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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 mounts¹, 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 deprioritised for now.
• Also, contempoarary mounts are not covered in equal detail.

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

Part 1: Identification rules:

The first step is identifying the mount type (bayonet, breech-lock or thread-mount). See the illustration of these three basic types below.

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

A breech-lock mount uses a locking ring to securely attach the lens to the camera. With some lenses that locking ring is part of the lens (making the lens fairly simple to identify as a breech-lock lens). If your lens has a rotatable locking ring, you’ve positively identified your lens as a breech-lock mount, jump here to continue its identification. (Besides these, there are breech-lock mounts with which the locking-ring is 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. If your lens does not have threads or a locking ring, it is a bayonet mount lens (or a breech-lock lens with the locking ring on the camera-end). Jump here for identifying your bayonet mount.

Group 1: Thread-mount lenses

Thread mount lenses are 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).

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).

58 mm diameter:

Mounting thread of Tamron Adapt-a-matic intermediate mount.

47 mm diameter:

Most probably an m47 mount (47 mm with thread pitch of 0,75 mm). The m47-mount is not to be confused with the m42 or T-mount (42mm diameter). See more about the m47-thread here.

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 adapter ring for the Miranda cameras’ internal 44 mm thread stuck on it. Try to see if you can unscrew the adapter?

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).

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 is an intermediate 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 confusion. There are basically five types of thread-mount lenses with a diameter of 39 mm.

Enlarger lenses:
Firstly, there are enlarger lenses (M39x1.0), which are easily identified by having aperture controls but lacking a focusing mechanism. Enlarger lenses are well-known to anyone who’s ever printed their own pictures. While not made for cameras, enlarger lenses are potentially useful for a wide range of photography – from macro work to close-to-normal use – but necessitate using a helicoid adapter or an adapter and a set of bellows.

Leica Thread Mount (LTM):
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 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”.
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 easiest way to distinguish LTM lenses from other 39 mm thread lenses is that LTM lenses always have:
1) an aperture mechanism,
2) a focusing mechanism, and
3) an inner cam that extends and withdraws as the lens’ focus is operated (this is the mechanism that facilitates the camera’s rangefinder coupling.
There is a wide variety of lenses available for LTM, 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.

Zenit M39:
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) a different thread pitch
b) 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).

Canon EX set lenses
Fourthly, there is the Canon EX-mount. The Canon EX line was a not entirely successful attempt by Canon to create a SLR system using set lenses. In this approach lenses were composed of two parts: a rear lens (3 elements, 2 groups) built in to the camera and an interchangeable front lens. Only a limited number of front lenses (EX 35/3.5; EX 50/1.8; EX 95/3.5; and EX 125/3.5) were offered before discontinuation. These lenses are easily distinguished by having ‘Canon EX’ on the name ring.

Paxette:
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.

38 mm diameter

Two alternatives:
• Opema viewfinder/rangefinder. While in many ways similar to the Leica thread mount, attempting to use Opema mount lenses on LTM bodies (or vice versa) risks damaging the lenses and threads.
• Argus model 21 viewfinder.

37 mm diameter

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

32-33 mm diameter

Likely the mount of an Argus C. As the design measure is in inches, accounts of the Argus C thread mount’s diameter in millimetres varies a bit.

26 mm diameter (M26x0,5)

Used by thread-mounted Robot -cameras. While very similar in diameter to C-mount (look below), the thread pitch is sufficiently different that cross-threading will certainly lead to damage.

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.

Group 2: Obvious breech-lock lenses

The weight here is on the ‘obvious’ because there are some breech-lock lenses, that 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 to lock the lens in place?

If no, jump 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.

If your lens has a breech-lock ring with a clamp such as the one in the picture below, you’re dealing with a T-4/TX mount lens. These were both intermediate lens mounts designed by Tokina but used on other brands of lenses (most notably Soligor and Vivitar).

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.

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.

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 Petri FT and Praktina (for 35 mm film) or Pentacon Six and Kowa Six (medium format film)

Group 3: 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 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…

First question: Is the bayonet male or female?*
If it’s a female bayonet, there are only a few choices, and you can jump right to the next stage.
If it’s a male bayonet, there are a lot of more choices. So next you will have to start looking at the mount in more detail. Continue your identification-adventure here.

* 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.)

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 Six: Canon FDn, Carl Zeiss Contarex, Exakta’s external bayonet, Miranda Bayonet, Tamron Adaptall and TopconUV bayonet.

The Miranda Bayonet is easy to distinguish, as it has four prongs/openings instead of the normal three, whereas lenses for the TopconUV bayonet can most easily be distinguished by that TopconUV bayonet lenses lack an aperture ring (the aperture ring is on the camera’s end of the mount) in combination with a dual-lever aperture control arrangement.

The Contarex mount is interesting as its female bayonet’s openings have a rather distinctive shape:

Canon FDn and Tamron Adaptall can be easily distinguished visually.

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 a pin 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.

A 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)

But merely knowing your lens has e.g. a locking pin is not enough. Next we will have to have a look at where that locking notch/locking groove/locking pin is.

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).

Note, please! 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.

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 .

And while you’re at it, as there is a veritable plethora of bayonet mounts (legacy and modern), merely the location of the notch/groove/pin might in some cases not be enough. Therefore, it makes sense to also look at the following characteristics:

• how many prongs does the bayonet have?
• does the mount have electronic contacts, how many, where are they?
• does the mount have communication pins or levers**, how many, and where
• does the mount have a slot-drive apparatus (looks like a big slot-type screw head, but it rotates when you twist the lens’ focus ring)

** Some Terminology:
• A communication pin is a control apparatus that moves in/out (e.g. Aperture pin in M42 auto lens).
• A communication lever moves (or is designed to move) sideways.
– Some communication levers are used to communicate (to the body) the lens’ selected aperture (they move when you twist the aperture control ring).
– Some communication levers are used to communicate (to the lens) that the lens should stop down to the aperture selected on the aperture control ring.
– Some communication levers are dual-function.

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)

Locking Pin Positions …

• 03:30 ==> EXA(kta), Topcon RE
  
• 04:30 ==> Olympus OM (note, pin is hidden under bayonet prong)
  
• 05:00 ==> Topcon RE
  
• 06:00 ==> Pentacon Six, Praktina, Altix, Petri FT (actually not a locking pin, but an orientation pin)
  
• 12:00 ==> Konica F (actually not a pin, but a claw that grasps pin on camera)

Locking Notch Positions …

Has locking notch (or something looking like a locking notch) at …

• 01:30 ==> Mamiya Z
  
• 02:30 ==> DKL or Zeiss Contaflex
  • Two quite similar mounts. Also, neither lenses have aperture rings, but easily identifiable, because
  • DKL
    • has two levers on the side of the flange that operate the aperture
    • Zeiss never made lenses for DKL mount
  • Contaflex
    • has no levers (and actually even lacks an aperture)
    • All Contaflex lenses made by Zeiss.
      
• 03:00 ==> Konica AR or Contax G
  • Contax G:
    • Has electronic contacts
    • Has slot-drive -screw
  • Konica AR:
    • No electronic contacts
    • No slot-drive screw
      
• 04:00 ==> Kiev Automat
• 05:30 ==>
  • Contax/Yashica (two levers)
  • Mamiya ES (one lever)
    
• 06:00 ==> Petri FT (actually an orientation device)
  
• 06:30 ==> Minolta SR
  
• 11:00 ==>
  • Yashica Pentamatic (has both locking groove and locking notch at 11:00)
  • Mamiya CS (has only locking notch on bayonet prong)
    
• 11:45 ==> Rollei QBM
• 12:00 ==> Pentax645

Has locking groove at…

• 01:30 ==> Yashica AF

• 03:00 ==> Canon EF, Canon RF, Contax G, Four Thirds, Fujica X, Micro Four Thirds, Nikon F, Nikon Z, Olympus OM AF/PF, and Sony/Minolta A
• (Yup, definitely the most usual arrangement, but there are subtle differences, that allow conclusive identification.)
  • Nikon Z
    • 4 bayonet prongs
    • 11 electronic contacts between 05:00 and 07:00, facing towards rear of camera
    • Locking groove in base of mount (on the flange)
    • No levers, no slot drive screw
  • Contax G
    • 4 Bayonet prongs
    • Electronic contacts between 10:00 and 12:00
    • Locking groove on rearmost end of bayonet (not on the flange)
    • Slot-drive screw at 12:30
    • No levers
  • Nikon F (Note: has multiple variants)
    • Three bayonet prongs (All variants)
    • Locking groove in the base of the mount (on the flange) (All variants)
    • One lever that operates aperture (all but newest variants)
    • Slot-drive screw at 10:45 (AF and AF-D variants)
    • One key identifier(for those Nikon F lenses that have electronic contacts) is that Nikon F electronic contacts are spring-loaded and point outward from the optical axis (as opposed to backwards).
      • 5 spring loaded electronic contacts (AF and AF-D variants)
      • 7 spring-loaded electronic contacts (AF-I)
      • 8 or more spring-loaded electronic contacts (AF-S)
  • FT (Four Thirds)
    • Three bayonet prongs
    • Locking groove in base of mount (on the flange)
    • 9 electronic contacts between 11:00 and 01:00, facing towards rear of camera
    • No levers, no slot-drive screw
  • MFT (Micro Four Thirds)
    • Three bayonet prongs
    • Locking groove in base of mount (on the flange)
    • 11 electronic contacts between 11:00 and 01:00, facing towards rear of camera
    • No levers, no slot-drive screw
    • n.B! MFT is a smaller version of FT, with two extra contacts.
  • Canon EF and RF:
    • Three bayonet prongs
    • Locking groove in base of mount (on the flange)
    • Electronic contacts arranged in two tiers between 11:00 and 01:00, facing towards rear of camera.
    • EF has maximum of 7 contacts, RF has 12
    • No levers, no slot-drive screw
  • Minolta A / Sony A (Note: has variants):
    • Three bayonet prongs (All variants)
    • 5 or 8 electronic contacts between 05:00 and 07:00, facing towards back of camera.
    • Slot-drive screw at 01:30 (on earlier variants)
    • One lever (on earlier variants)
  • Fujica X (not Fuji(film)-X):
    • Three bayonet prongs
    • Locking groove in base of mount (on the flange)
    • Two levers (stop down and aperture indicator)
    • No electronic contacts, no slot-drive screw.
  • Olympus OM (Autofocus/Powerfocus variant)
    • Three bayonet prongs
    • One lever
    • Slot-drive screw at 01:00
    • Lenses lack aperture and focus ring
    • Three backward-facing, spring-loaded electronic contacts (Autofocus variants)
    • No electronic contacts (Powerfocus variants)
• 7:30 ==> Agfa Ambi Silette

• 9:45 ==> 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 or less electronic contacts between 11 and 1 o’clock
      
• 10:00 ==> Sony E and FE
  
• 10:30 ==> Leica L, Fujifilm X or Mamiya 6
  • 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
  • Mamiya 6:
    • Three bayonet prongs
    • 8 electronic contacts between 11 and 1 o’clock
    • one lever and a rangefinder cam.
      
• 11:00 ==> Yashica Pentamatic (has both locking groove and locking notch at 11:00)

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.
• The Konica F mount does not technically have a pin, groove or notch, but a claw that grasps a pin on the camera body.
• The Pentax 110 mount does not have a pin, groove or notch, but is easy identify as it has only two bayonet prongs (and is tiny)

Part 2: 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.

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Altix

To be added later, sorry.

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Agfa Ambi Silette

Key characteristics of the mount of Agfa Ambi Silette lenses:
[1] Locking groove at 7:30.
[2] rangefinder cam (moves in tandem with focusing motion).

Note please: The Ambi Silette mount is rather unusual as it (looking from straight behind) seems to not be either a bayonet, breech-lock nor thread-mount. To understand the locking mechanism of the Ambi Silette, another angle is more illuminating:

[3] locking groove that spans the circumference of lens.

Details of the Agfa Ambi Silette mount
See the JAPB article on the Ambi Silette mount.

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C-mount

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

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Canon EF-family

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.

Details of the Canon EF mount
See the JAPB page on the Canon EF mount (family)

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Canon FD

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.

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.

Details on the Canon FD mount:
See the JAPB article on the Canon FL, FD and FDn mounts.

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Canon FDn

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.

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).

Details on the Canon FDn mount:
See the JAPB article on the Canon FL, FD and FDn mounts.

Canon FL

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.

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.

Details on the Canon FL mount:
See the JAPB article on the Canon FL, FD and FDn mounts.

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Canon R (Canomatic)

This refers to the Canon R-mount (1959-1964), which is the predecessor to the Canon FL -mount. Now that Canon’s new mirrorless mount is called RF but sometimes abbreviated as only R, I’m thinking this mount should be renamed the Canonflex mount (for the series of cameras that used it) or, better yet, the Canomatic mount (because that’s how Canon referred to these lenses).

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

Details on the Canon R mount:
See the JAPB article on the Canon R mount.

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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.

You can read the JAPB article on the Canon RF mount.

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Contarex

Key characteristics of the Contarex-mount:
[1] Female bayonet for three bayonet prongs
[2] Locking groove at about 09:30
[3] Aperture control ring (rotates around the optical axle and operates the aperture mechanism directly)

Details on the Contarex-mount
See the JAPB article on the Contarex-mount.

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Contax G

Key characteristics of the Contax G -mount:
[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).

Details on the Contax G -mount
See the JAPB page on the Contax G -mount

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Contax / Kiev

The Contax / Kiev -mount is relatively hard to identify using the logic otherwise used on this page, because
a) the Contax / Kiev – mount is actually two mounts.
b) the inner mount rotates (hence, lenses have no ‘up’) and the inner bayonet’s prongs are not very visible.

Explaining the Contax / Kiev mount is easiest if we start by looking at the camera-end of the mount:

[1] Inner bayonet (three prongs), partly obscured.
[2] Inner bayonet hold-down clamp
[3] Outer bayonet (three-pronged)

The inner bayonet on a Contax / Kiev camera is intended to rotate in its entirety (including the lens), whereas the outer bayonet is stationary. The rotation of the inner mount is coupled to the Contax / Kiev camera’s rangefinder (see distance scale on outer end of inner mount).

Only lenses that have ≈ 50 mm in focal length can be used on the inner mount so that the range finding works. Wider and narrower lenses can be used on the outer mount, and outer mount lenses have a tube that extends into the inner mount to and engages with (but does not latch onto) the inner bayonet prongs, thereby activating the rangefinder. (Once you know this, you’ll also understand better why the inner and outer bayonets on lenses look like they do.)

[4] Three-pronged bayonet (engages with three-pronged inner bayonet (1))
[5] Inner bayonet lock pin (locks with inner bayonet hold-down clamp (2))

[6] Three-pronged bayonet (clamps onto outer bayonet)
[7] Outer bayonet release clamp
[8] Inner tube (engages with rangefinder mechanism).

Whereas the outer bayonet mount is entirely stationary, the inner tube [8] rotates when the lens is focused, thereby facilitating rangefinder coupling.

Details on the Contax / Kiev mount:
See the JAPB page on the Contax / Kiev mount.

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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. First, let’s make sure we can identify it correctly.

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

Details on the C/Y mount:
See the JAPB page on the Contax/Yashica mount.

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D-mount

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

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DKL-mount

The DKL mount is a bit of an odd duck (not a one-of-its-kind, but still far from a common mallard) in the family of interchangeable lens camera mounts. Be sure to also read the page giving details on the DKL mount to understand what makes it special (unless you’re an DKL-expert, in which case I wish you read it in order to help me extend the article).

Let’s see how to identify DKL lenses:

Key characteristics:
[1] Eccentrically shaped bayonet (note please, some DKL lenses do not share this exact shape… read on.)
[2] Locking notch at about 02:30
[3] Aperture stop-down lever (this operates the aperture stop-down and moves independently of [4])
[4] Aperture designator lever (this sets the aperture to stop down to. When this lever is moved, also lever [3] moves).

Some things are immediately apparent even from one picture. The lens mount has a very unusual shape: Instead of a barrel that has three or four prongs sticking out, this shape is … well, eccentric.
What is less apparent from a picture is that the mount is actually quite small (maximum diameter of shape highlighted above: ≈35 mm) and that all but the earliest DKL lenses lack an aperture ring (aperture was controlled on the camera).

Things get a bit more complicated by the fact that the DKL mount was not one mount, but constitutes a 7-member strong family of mounts where some of the manufacturers (Braun, Edixa, Kodak, Voigtländer) that used the DKL mount started adding proprietary obstructions to disable other manufacturers’ lenses from being mounted. Therefore, even though your lens’ mount shape might differ significantly from the shape shown above (a Kodak Retina variant), it might still be a DKL lens.

While I do repeat that you should read the DKL page, I’ll mention something positive here: Most DKL adapters are able to use all of the DKL variants successfully.

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Exakta

The Exakta bayonet is not only a very early lens mount (Introduced 1936), it is also a family of mounts. At the core of that family is always a symmetrical three-pronged bayonet mount:

Identifying the mount
For a bayonet mount, the Exakta-mount is very simple, but there are some quirks (we’ll get to them in a second):
[1] Three-pronged bayonet with three identical prongs, spaced 120 degrees apart
[2] Locking pin at 3:30 o’clock.

And then the quirks:
If you’re interested, JAPB offers a detailed article on the Exakta mount and all its variants. However, if you’re more interested in a surface level discussion, read on:
The Exakta-mount was in active use for more than 40 years, and during that time a lot happened in the photographic world so while the basic setup of the Exakta-mount (as depicted above) stayed the same, a lot of extensions to that basic setup were also manufactured. While all these cannot be addressed here, the most important were:

1. One often encounters Exakta lenses which have a pod-like construction attached to the side of the lens (see pics above). 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 that have those pods are very simple to identify, these pods started appearing on Exakta lenses only in 1956 and were never used by all manufacturers.
2. The Exakta-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 picture below
3. The Exakta-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, and especially Topcon was quite prolific in implementing such extensions. Hence, your lens’ mount may show features not visible in these pictures. For an in-depth discussion of the Topcon-Exakta variants, go to the Topcon RE-section.
4. Towards the End – as a sort of dying gasp – The Exakta RTL body was launched. While that body could use all old Exakta lenses, it also introduced its own method for stopping down the aperture, and those lenses are not quite compatible with the other Exakta cameras.

As a result, there are some incompatibilities between various Exakta cameras and lenses, most of which however do not matter when intending to adapt the lens

Details on the Exakta mount:
See the JAPB page on the Exakta mount.

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Four thirds

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

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Fujica X

[1] Three-pronged bayonet mount
[2] Locking groove at 3 o’clock (on base of flange)
[3] Aperture indicator lever (moves with aperture ring)
[4] Aperture stop-down lever
[5] Metallic protrusion at 6 o’clock (function unknown, but is characteristic of Fujica X lenses)

Details on Fujica X mount:
See the JAPB article on the Fujica X mount.

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Fujifilm X

To be added later, sorry.
If you want to support this page, be in touch and send pictures of lens mounts.
See the JAPB article on the Fujifilm X mount

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Icarex BM

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.

Details on the Icarex BM mount:
See the JAPB page on the Icarex BM mount.

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Kiev Automat

Key characteristics of Kiev Automat lenses:
[1] Three-pronged male bayonet mount with locking notch at 04:00
[2] Aperture setting lever

Details on the Kiev Automat mount
See the JAPB article on the Kiev Automat mount

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Konica AR

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).

Details on the Konica AR mount:
See the JAPB page on the Konica AR mount.

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Konica F

[1] Three-pronged unsymmetrical bayonet
[2] Bayonet locking claw at 12 o’clock (interacts with retractable locking pin on camera body)
[3] Aperture actuator (interacts with similar on camera body)
[4] Early (For Konica F camera) lenses would have an extra lever reaching beyond the lens proper (precise location of that lever depends on set aperture)

Details on Konica F-mount
See the JAPB article on the Konica F mount.

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Leica L

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

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Leica M

To be added later, sorry.
If you want to support this page, be in touch and send pictures of lens mounts.
See JAPB article on the Leica M mount

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Leica R

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

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

The standard LTM mount is a thread mount that 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.

Regarding identification, the Leica thread mount has no other distinguishing features except
a) a thread mount, with
b) a 39 mm diameter.
(and even that does not guarantee that the lens is a LTM lens. See above.)
c) a 26 TPI thread pitch (that cannot easily be measured)

Characteristics of an LTM mount:
[1] 39 mm diameter threads
[2] Inner cam that moves forward/backward in tandem with focusing action.

Details on the LTM mount:
See the JAPB page on the LTM mount.

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M42

As noted, the M42 is the quintessential general thread mount for SLR cameras, 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 that each add elements to the basic thread mount interface (stop down pins, aperture indicator levers, even electronic contacts) users should be aware of because they often radically change the appearance of the lens mount and might even impact adaptability.

Note: While we will try to cover the breadth of the M42 mount here, we will only do so for identification purposes. I recommend you look at the JAPB page for the M42 mount for further details.

M42 plain (just the thread mount)

This is the earliest version of the M42 mount, and was used only on lenses that either had a direct aperture coupling or preset lenses.

Identifiable traits:
[1] 42 mm diameter thread (with 1.0 mm thread pitch]

M42 auto

This version of the M42 mount adds a simple pin (moves in/out) that allows the body to stop down the lens’ aperture (thereby enabling open-aperture composition and focusing) for metering and picture-taking. This is likely the most numerous form of the M42 mount.

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

(NOTE! While the most typical implementation of the camera-driven stop-down mechanism is a simple, thin pin, there are lenses in which the pin is considerably thicker)

M42 with two-way communication

To circumvent the need to manually stop down the lens (for metering purposes) the lens needed to be able to ‘report’ to the body what aperture the user had selected. To facilitate this, several proprietary approaches were devised, the most usual (and typical) of which will be shown.

The Pentax way (1969)

The Picture above shows the mechanical aperture communication method pioneered by Pentax starting in 1969:
[1] 42 mm diameter thread (with 1.0 mm thread pitch]
[2] pin for stopping down lens to user-defined aperture (used in automatic mode).
[3] aperture linkage lever, directly coupled to the aperture ring, thus allowing a compatible body to read the selected aperture.
[4] Feeler pin to activate the auto-setting on the auto/manual selector
[5] Switch for selecting between auto(matic) and manual aperture mode.
[6] Rotation stopper to make sure lens is mounted at correct angle (may hinder using the lens on cameras not designed with this in mind).

The Fujinon way (1972)

Introduced by Fuji Photo Film in 1972, this proprietary system only found on Fujinon M42 lenses extends the basic setup of M42 auto lenses:
[1] 42 mm diameter thread (with 1.0 mm thread pitch];
[2] pin for stopping down lens to user-defined aperture;
[7] backwards protrusion of the aperture ring that allows a compatible camera body is able to read the aperture ring position directly;
[8] locking groove in the base of the flange to secure that the lens is mounted at the correct rotational angle.

While the locking apparatus was implemented in a way that did not hinder cross-compatibility, the aperture ring protrusion means that Fujinon lenses that have this protrusion can not be mounted on most M42 cameras (and even make trouble with some adapters). As a result of this, you will find many lenses where the protrusion has been filed away.

The Mamiya way (1974)

In a move that resembles Fuji’s 1972 move (above), Mamiya in 1974 introduced their own addition to the M42 mount (these lenses have the abbreviation ‘SX’ in their name), which is characterised by:
[1] 42 mm diameter thread (with 1.0 mm thread pitch];
[2] pin for stopping down lens to user-defined aperture;
[7] pin in the aperture ring that allows a compatible camera body is able to read the aperture ring position directly (moves with aperture ring);
[8] locking groove in the base of the flange to secure that the lens is mounted at the correct rotational angle.

Like with the Fujinon adaptation of the M42 mount, the locking apparatus was implemented in a way that did not hinder cross-compatibility. However the aperture ring pin means that Mamiya lenses that have this pin can not be mounted on most M42 cameras (and even make trouble with some adapters). As a result of this, you will find many Mamiya SX lenses where the pin and even the base of the aperture ring has been milled away.

Further details can be found in the JAPB article on all Mamiya 35 mm SLR mounts.

The Praktica way (1969)

The electronic approach to aperture communication was pioneered by the East German camera industry (Carl Zeiss Jena, Pentacon, Meyer-Optik), and was the first instance of electronic communication between camera and lens. This approach to extending the M42 mount was introduced with the Praktica LLC camera in 1969.

The Picture details the ‘electronic’ version of the M42 mount.
[1] 42 mm diameter thread (with 1.0 mm thread pitch]
[2] pin for stopping down lens to user-defined aperture (used in automatic mode).
[5] Switch for selecting between auto(matic) and manual aperture mode.
[9] Three spring-loaded electronic contacts on the lens’ mount flange

Further details on the M42 mount:
See the JAPB page on the M42 mount.

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m47 thread

The m47 is technically not a lens mount (as there were no cameras made for m47), but is an intermediate mount. The idea of m47 lenses is not to be mounted directly on a camera, but to be screwed into an adapter that is then mounted on a camera.

As the m47 does not facilitate any lens-body communication, it is usually available only on older SLR lenses.

Online information on the m47 intermediate mount is scarce, even the name is not clear (it is sometimes referred to as ‘T-thread’, which – problematically – is also used as a synonym for the T-mount). Calling it the m47 mount is a JAPB initiative.

Specifications (rough measurements):
Thread: 47 mm diameter; 0,75 mm pitch
Flange Focal distance: ≈48,6 mm

Adapting a m47 lens
Your best bet for mounting a m47 lens, is to hunt down an original adapter-ring, such as the m47-to-Minolta SR adapter pictured below.

Mamiya 6

Key characteristics of Mamiya 6 mount:
[1] Three-pronged male bayonet
[2] Locking notch at 10:30
[3] 8 electronic contacts (spring-loaded at the camera-end) between 11 and 1.
[4] Rangefinder cam (moves forward/backward when changing focus)
[5] Leaf shutter tensioning lever

Details on the Mamiya 6 mount:
The Mamiya 6 mount is used by the Mamiya 6 medium format interchangeable lens rangefinder camera.
More details to be added later.

Mamiya NC/CS mount

Key characteristics of the Mamiya NC/CS mount:
[1] Three-pronged male bayonet mount with locking notch at 11:00
[2] Aperture stop-down pin.

Details on the Mamiya NC/CS mount
See the JAPB article on the all Mamiya 35 mm SLR mounts.

Mamiya XTL/ES mount

Characteristics:
[1] Three-pronged male bayonet with locking notch at about 05:30
[2] Aperture stop-down lever

Details on the Mamiya XTL/ES mount
See the JAPB article on the all Mamiya 35 mm SLR mounts.

Mamiya Z/E mount

[1] Three-pronged bayonet with tapered edges and lock notch at 01:30.
[2] Aperture communication prong (interacts with camera). Location indicative as moves with aperture ring.
[3] Aperture control lever
[4] Two banks of electronic contacts. 6+4 contacts on E-class lenses; 6+5 contacts on EF-class lenses.

Details on the Mamiya Z/E-mount
See the JAPB article on the all Mamiya 35 mm SLR mounts.

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Micro four thirds

The Micro four thirds (also MFT) is a multi-company lens mount for mirrorless cameras and the successor of the Four Thirds dSLR mount.

Key characteristics of the micro four thirds/MFT mount:
[1] Three-pronged bayonet.
[2] Locking groove at 3 o’clock.
[3] 11 electronic contacts (spring-loaded at the camera-end) between 10:30–1:30.

Details on the Micro Four Thirds mount:
See the JAPB article on the Micro Four Thirds mount.

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Minolta A

Note: This mount is variously referred to as Minolta A, Minolta alpha, Sony A, Sony alpha. In the 40-ish year lifespan of the Minolta A mount, some variant were introduced that also impact the mount-end of lenses. (See the JAPB article on the Minolta A mount for details).

Early version: Classic (1985->) and RS lenses (1990->)

Key characteristics of the ‘classic’ and ‘RS’ Minolta A / Sony A mount:
[1] Locking groove at 3 o’clock.
[2] Three-pronged bayonet
[3] Slot-drive screw (only on ‘classic’ and ‘RS’ lenses)
[4] Aperture stop-down lever (on some lenses)
[5] 5 electronic contacts (spring-loaded at the camera end)

SSM/SAM (and DT) (2003->)

Since the introduction of in-lens focus motors, many new Minolta/Sony A lenses mounts have corresponded to:

Key characteristics of the SSM/SAM Minolta A / Sony A mount:
[1] Three-pronged bayonet (heavier/more premium lenses had a metal bayonet)
[2] Locking groove at 3 o’clock.
[3] 8 electronic contacts (spring-loaded on the camera-end)
[4] Aperture stop-down lever (on some lenses)

(note please that i do not have pictures of the Minolta A mount’s Xi variant)

Further details on the Minolta A mount
See the JAPB article on the Minolta A mount.

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

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)

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. In the earliest days of the SR mount, both Minolta and third-party manufacturers offered lenses for the SR-mount that did not have an automatic aperture.
Thirdly, the X-600 lenses are MD-lenses with an extra prong readable by the Minolta X-600 body. See picture below.

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Miranda bayonet

The Miranda mount is in some ways quite exceptional, because (on the camera end), users could choose between two mounts – Miranda’s proprietary four-pronged female bayonet (quite a unique approach in itself) and a 44 mm diameter thread mount (inside of that bayonet mount). That 44 mm thread mount would – by using adapters – allow for adapting a wide range of other lenses, most importantly M42 thread mount lenses. Here we will focus on the 4-pronged bayonet mount, so let’s make sure we can identify it.

[1] Four-pronged female bayonet mount
[2] Aperture stop-down lever
[3] Aperture preview button (stops down lens to selected aperture)
[4] Lens release button
[5] Bayonet lock (operated by lens release button)
n.B! This is a relatively early Miranda lens, and while the basic mount configuration (elements 1,2,4,5) stayed the same throughout, later lenses omitted the aperture preview button, and added an interface for communicating selected aperture.

Details on the Miranda mount:
Not quite there yet, sorry.
In the meantime, see the pages of the Miranda Historical Society (archived)

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Nikon F

The Nikon F-mount has been in continuous use since 1959, and has – unavoidably – progressed a bit during the decades. Due to the existence of an article dedicated to the Nikon F-mount, 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.

Nikon F – Pre-AI

Identifying characteristics:
[1] Three-pronged bayonet with straight edges.
[2] locking groove at 3 o’clock
[3] aperture stop-down lever
[4] “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.

However, to discern the main difference between a Pre-Ai and Ai lens, it might be useful to look at the lens a bit from the side:

[5] Notice, that the base of the aperture ring (black) protrudes beyond the lens mount (chrome) all around the lens. This is a key characteristic of a Pre-Ai lens and is what makes (unmodified) Pre-AI lenses incompatible with most Nikon SLR cameras post 1977 and all but a few dSLR’s.

Nikon F- AI (‘automatic indexing’)

The main characteristics of Pre-Ai-lenses are still there, but the base of the aperture ring has been trimmed back to make way for two extensions:
[6] The AI tab (that interacts with almost all SLRs and dSLRs to communicate the selected aperture)
[7] Another tab intended for a functionality that was never used.

Nikon F – AI-s

The change from Ai to Ai-s was necessary to implement functionality pertaining to increased automation. You can read a detailed explanation of all the changes here.

Again, all the previous characteristics of the Nikon F mount are there, but:
[8] The key change going from Ai to Ai-s has to do with how the aperture lever is calibrated and is not outwardly visible, but
[9] This little notch exists to tell your camera (and you) that you’re dealing with an Ai-s lens.
[10] After launch of the Ai-s lenses, some lenses started losing their rabbit ears while others retained them.

Nikon F – AF and AF-D

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

Again, the mounts of AF/AF-D lenses are evolutions of Ai-s mounts in the sense that all features are added features.

The following characteristics are new (among AF/AF-D lenses compared to Ai-s lenses):
[12] Slot head for body-driven autofocus.
[13] (spring-loaded) Electronic contacts
[14] Rabbit ears gone (no AF lenses have them as factory installed)

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.

Nikon F – 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)..

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Nikon S

To be added later, sorry.
If you want to support this page, be in touch and send pictures of lens mounts.
See the JAPB article on the Nikon S mount.

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Nikon Z

To be added later, sorry.
If you want to support this page, be in touch and send pictures of lens mounts.
See the JAPB article on the Nikon Z mount

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Olympus OM

Let’s look at identifying OM mount lenses:

[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.

Details on the Olympus OM mount:
See the JAPB page on the Olympus OM mount.

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Olympus OM AF/PF

Olympus First line of autofocus lenses (1986-1991) use a modification of the Olympus OM mount.
Let’s look at being able to identify the mount.

[1] Three-pronged bayonet mount, with tapered prongs.
[2] Slot-drive screw at 1:00 o’clock.
[3] Three spring-loaded electronic contacts between 5:00 and 6:00 o’clock (Autofocus lenses only)
[4] Aperture stop-down lever.
[5] Locking groove at 3:00 o’clock
[not visible] Lenses lack both aperture and focus rings.

Details on the Olympus OM AF/PF mount:
Some details are available as part of the JAPB page on the Olympus OM mount.

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Olympus F (pen)

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

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Pentax 110

[1] Two-pronged bayonet mount.
No communication pins or levers;
No grooves notches or lock pins;
No aperture control, only a focus ring.

One more thing: The picture belies a central characteristic of the Pentax-110 mount: its size. As the Pentax-110 mount was used by the eponymous camera, which in turn used 110-size film cassettes, the optics were amazingly small. The measurements of the 24mm f/2.8 (the system’s normal lens) were: 14 mm long; 29 mm diameter; 11 grams (!). See below for a picture of this lens mount with a calliper for scale:

Details on the Pentax 110 mount:
To be added later, sorry.

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Pentax 645

The Pentax-645 family of cameras are all medium format (6cm X 4,5 cm) cameras, but can clearly be divided into three generations:
• Pentax 645 (manual focus) camera and the Pentax-A (645) lenses (1984–1997)
• Pentax 645N/645NII (autofocus) camera and the Pentax-FA (645) lenses (1997–2010)
• Pentax 645D/Z (digital, autofocus) camera and the Pentax-D FA lenses (2010–>

Each camera generation has been backwards compatible (you can use manual lenses on autofocus cameras and you can use all lenses on the digital bodies). However, there are differences between the respective mounts:

Pentax-A 645

Key characteristics of the mount of Pentax-A 645 -lenses:
[1] Three-pronged bayonet mount, with locking notch at 12:00
[2] Aperture indicator lever (communicates selected aperture to camera)
[3] Aperture stop-down
[4] Electronic contacts between 5:00 and 7:00. Whether these identify only the lens’ max. aperture or actually identify the lens is unclear to me.

Pentax-FA 645

Key characteristics of the mount of Pentax-FA 645 -lenses:
[1] Three-pronged bayonet mount, with locking notch at 12:00
[2] Aperture indicator lever (communicates selected aperture to camera)
[3] Aperture stop-down
[4] Electronic contacts between 5:00 and 7:00. Whether these identify only the lens’ max. aperture or actually identify the lens is unclear to me.
[5] Slot-drive screw for body-driven autofous.

Pentax-D FA 645 mount
(We have no high-resolution pictures of this mount. Sorry)

Details on the Pentax 110 mount:
To be added later, sorry.

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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)

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, four 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.

Details on the Pentax K mount
See the JAPB page on the Pentax K mount.

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Petri FT

Key characteristics of the mount of Petri FT-mount lenses
[1] Breech-lock mount with three lugs, with something resembling a locking notch at 6 o’clock
[2] Orientation pin at 6 o’clock (on a camera, this always goes up)
[3] Aperture stop-down lever
[4] Aperture control pin (only on FT EE lenses)

The Petri mount is a breech-lock mount, where the breech-lock’s friction ring is on the camera’s end, meaning that (when only looking at a lens) one might mistake it for a bayonet mount.

Details on the Petri FT mount:
See the JAPB article on the Petri FT mount.

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Praktica B

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).

Details on the Praktica B mount:
See the JAPB page on the Praktica B mount.

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Praktina

Key characteristics of the mount of Praktina-mount lenses
[1] Orientation pin at 6 o’clock (on a camera, this always goes up)
[2] Breech-lock mount with three lugs
[3] Aperture stop-down pin (preset lenses will not have this).

The Praktina mount is a breech-lock mount, where the breech-lock’s friction ring is on the camera’s end, meaning that (when only looking at a lens) one might mistake it for a bayonet mount.

Note please, that the Praktina mount has identical characteristics with the Pentacon Six mount, but as the Pentacon Six mount is for a medium format camera, the Pentacon Six mount is significantly larger than that of regular 135-format film cameras.

Details on the Praktina mount:
See the JAPB page on the Praktina mount.

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Rollei QBM

Key characteristics of the mount of Rollei QBM lenses:
[1] Three pronged male-type bayonet mount with a profusion of straight, tapered and very shallow prongs and lock notch at 11:45.
[2] Aperture stop-down pin (QBM lens versions I–IV)
[3] Aperture indicator (moves in the groove together with aperture ring, spring-loaded for backwards compatibility) (QBM lens versions II–IV)
[4] Max aperture indicator ‘step’ (a furrow going all the way around the lens mount, the depth of which is read by the camera to discern max aperture) (QBM lens version IV)
(The difference between lens versions II and III have no impact on the mount, and relate more to ergonomics)

Details on the Rollei QBM mount:
See the JAPB Page on the Rollei QBM mount.

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Sigma SA

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

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T-mount

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

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Tamron Adaptall

Key Characteristics of Tamron Adaptall lenses
[1] Female bayonet mount with three openings
[2] Adapter release lever
[3] Aperture stop-down mechanism (press to stop down lens)
[4] Adapter orientation indicator

Details on the Tamron Adaptall mount
The Tamron Adaptall (versions 1 and 2) is not strictly speaking a lens mount, but is instead an intermediate mount.

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Tamron Adapt-a-matic

Key Characteristics of Tamron Adapt-a-matic lenses
[1] 58 mm thread mount (Does not protrude. You have to know to look for it)
[2] Orientation pin to help orient adapter
[3] Opening (dark) for adapter’s lever to couple with aperture mechanism lever (silver)

Details on the Tamron Adapt-a-matic mount
The Tamron Adapt-a-matic is the predecessor of the Tamron Adaptall mount and is not strictly speaking a lens mount, but is instead an intermediate mount.

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Tokina T-4

Key Characteristics of Tokina T-4 lenses
[1] three-opening breech-lock mount (1 and 4 rotate together, independent of lens barrel. Hence their angle vis-a-vis the lens barrel might vary)
[2] orientation notch at the bottom of breech-lock
[3] alignment fork, rotates together with aperture ring.
[4] locking clamp with ratchet mechanism with arrows for O(pen) and L(ock). Silver tongue next to L must be pressed to unlock ratchet,

Details on the Tokina T-4 mount
The Tokina T-4 mount is not strictly speaking a lens mount, but is instead an intermediate mount. For more details, see the JAPB article on the T-4 and TX mounts.

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Topcon RE

Some might say that the Topcon RE (correct name: RE.Auto-Topcor) is not a lens mount, but merely an extension of the EXA (Exakta) mount, and they would be correct, especially as the Topcon RE mount is backwards compatible with EXA lenses. Even so, because the Topcon RE mount is visually quite dissimilar from typical Exakta lenses, presenting the Topcon RE mount is prudent. Let’s start by making sure we can identify it.

[1] Three-pronged (male) bayonet. Notch at position 1 is a later addition to the mount (it is absent from most Topcon RE lenses)
[2] Locking pin at 3:30 o’clock (the ‘Exakta pin’)
[3] Second locking pin at 5:00 o’clock (the ‘Topcon RE pin’)
[4] Aperture stop-down lever
[5] Aperture indicator prong/notch (position changes with aperture ring; may be part of the aperture ring as in this example or be on the flange)

Notes:
• Topcon’s Exakta-mount lenses came in 4 generations and this one image does not do them justice.
• The Aperture indicator prong/notch is part only of the last (most popular) generation.

See more on the Topcon RE mount:
In JAPB’s article on the Exakta mount there is a long section devoted to the Topcon-Exakta mounts .

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Topcon UV

Key characteristics of Topcon UV mount:
[1] Three-pronged female bayonet mount
[2] Orientation pin
[3] Lens release button
[4] Dual-lever aperture control system

Another very important identification trait of a TopconUV mount lens is that the lens entirely lack aperture controls as those controls were mounted on the body. See pictures below.

Details on the Topcon UV mount:
See the JAPB page on the Topcon UV mount.

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Yashica AF (aka Yashica 230 or Yashica/Kyocera)

Key characteristics of the mount of Yashica AF lenses:
[1] Three-pronged male bayonet. All edges tapered.
[2] Locking groove at roughly 01:30 o’clock.
[3] Slot-drive screw at roughly 11:30 position
[4] Stop-down lever
[5] Electronic contacts between 04:00 and 06:00 (5 on regular AF lenses; 10 on power zoom lenses).
[not visible] Yashica AF lenses lack an aperture ring.

Details on the Yashica AF mount:
See the JAPB page on the Yashica AF mount.

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Yashica Pentamatic

The Yashica Pentamatic mount was a short-lived (1960–≈1963) bayonet mount used by Yashica 35 mm SLRs.

Key characteristics of the mount of Yashica Pentamatic lenses:
[1] Three-pronged male bayonet. All edges tapered. Locking notch at 11:00 position.
[2] Locking groove at 11:00 o’clock.
[3] Dual-purpose aperture stop-down and aperture indicator lever.

Details on the Yashica Pentamatic mount:
See the JAPB article on the Yashica Pentamatic mount

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Zeiss Contaflex

The Zeiss Contaflex mount looks like a lens mount, but is technically not a lens mount as it is not used to mount a lens to a camera body. Instead, it is intended to connect the front-end and back-end of a set lens. As a result, the front-ends of set lenses can neither be used nor adapted as such.

Key characteristics of the mounting interface of Zeiss Contaflex/ Pro-Tessar lens front-ends:
[1] Three-pronged male bayonet. Non-symmetrical, all inner edges tapered.
[2] Locking notch at ca 02:30 o’clock
No other interfaces.

Details on the Zeiss Contaflex / Pro-Tessar ‘lens mount’:
See the JAPB article on the Contaflex mount.
Unless you’re familiar with the concept of set lenses, it might be worth a read.

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Zenit M39

Z39 is short for the Zenit M39 mount – a lens mount using a 39 mm thread (like the Leica Thread Mount), but a flange focal distance measuring 45,2 cm.

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Thanks to…

Thanks to the following individuals who have collaborated in this guide:

• Anton G for donating images for Mamiya 6, Pentax-A 645, Pentax-FA 645, Agfa Ambi Silette, Minolta A (SAM) and helping decipher the functionality of the mount.
• Gerjan v. Oosten for elucidating some of the specifics of the Pentax/Takumar extension of the M42 mount.
• Kari J for lending me his Contax G lenses and adapetrs.

Version history

Sept.2020: Added EXA mount
Oct.2020: Added Icarex BM mount
Feb.2022: Added Topcon UV mount
Mar.2022: Restructured entire article, added DKL mount, Fujica X, Konica F, Pentax-110 and Contax / Kiev mounts
Apr.2022: Added Pentacon Six, Praktina and Petri FT mount
May 2022: Added Olympus OM Autofocus/Powerfocus, Mamiya Z, Topcon RE and Miranda mount
Sept.2022: Added Minolta A mount
Dec.2022: Added Yashica AF mount
Jan.2023: Added Rollei QBM mount
Feb.2023: Added Tamron Adaptall mount
Aug.2023: Added Canon R and Zeiss Pro-Tessar mount
Jan.2024: Added Yashica Pentamatic mount
Mar.2024: Added Tamron Adapt-a-matic and Tokina T-4 mounts
Jun.2024: Improved illustrations.
Jun.2024: Added Mamiya CS and Mamiya ES mounts
Aug.2024: Added Agfa Ambi Silette, Mamiya 6, Micro Four Thirds, Pentax 645 mounts
Nov.2024: Added Kiev Automat mount

Footnotes

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1. Currently Wikipedia lists 108 lens mounts, and I know of several that are not listed. ↩︎