West Yorkshire Cameras SLR Lens

35mm SLR Lens mount identification guide

It’s taken me three or four years to be able to tell by sight what lens fits which camera without having to try a lens on every camera within reach to figure it out. If, like me, you are also experiencing lens mount misery, read this handy quick guide to the most common lens mounts, and banish those bayonet blues.

Nikon F

Nikon’s lens mount is simple, and confusing at the same time. The simple part, is that the bayonet has remained the same since the introduction of their first SLR, the F. I suppose the intention was that any Nikon SLR lens fits any Nikon camera. But it’s not quite happened that way in practice. The oldest “non-ai” lenses won’t fit on a big fancy modern DSLR camera, but they will fit the cheaper ones. They also won’t fit some of their film cameras of a particular age, unless they have a specific feature that allows it, or the lens has been retrofitted with an AI mount, or DIY converted. Fancy modern “G” lenses won’t be compatible with older, non electronic cameras. And AF-D lenses will fit just fine on any camera, but won’t autofocus unless the camera has a built in motor.

If you’re not up to speed on which lenses are compatible with which cameras, it’s a bit of a minefield. Ken Rockwell explains the differences and provides a chart detailing which camera is compatible with which lenses, here.

I will outline the visual differences here:

Nikon Ai

The easiest way to visibly identify a Nikon AI mount lens is by looking for the ‘Rabbit Ears’ (at 12 o’clock in this photo). An AI lens will have small cutouts so that more light can fall on the smaller aperture lettering. A Non-Ai lens almost always has solid rabbit ears. If these ears are not present for some reason (they are removable) check the side of the lens for aperture numbers in both larger and smaller lettering. This is indicative of a Nikon Ai or Ai-S lens – an Ai-S lens will be easiest to identify if the smallest aperture number is in orange (E.G f/22, f/32). A third indicator is a small ridge around the lens mount (seen in the second photo, beginning just underneath the smaller f/8 lettering). This is the Aperture Index (AI) by which the lens type is named, and it tells the camera what aperture the lens is set to.
West Yorkshire Cameras Nikon SLR Lens
West Yorkshire Cameras Nikon SLR Lens

Nikon Non-Ai

West Yorkshire Cameras Nikon SLR Lens

West Yorkshire Cameras Nikon SLR Lens

Nikon AF / AF-D

At the mount: contacts for the electronics, small slotted screw which drives the autofocus. On the side: the AI numbering is all white except for f/22 which is in orange. The general colour scheme is black, white and orange. The AF-D lenses are almost always black bodied plastic construction.
West Yorkshire Cameras Nikon SLR Lens
West Yorkshire Cameras Nikon SLR Lens


Canon changed its lens mount when introducing Autofocus lenses to the market. The older FD lenses are not compatible with newer cameras, and vice versa.

FD Breechlock

The older type lens mount usually found on earlier FD lenses. The entire silver ring rotates to attach the lens, whist the body and glass of the lens remains stationary – rather than rotating the lens to attach it to the camera as most modern lenses do.
Canon FD mount is easy to identify, as the bayonet on the lenses is “female” rather than the standard arrangement of the lens bayonet being male.
West Yorkshire Cameras Nikon SLR Lens

“New” FD

New FD is the later style Canon FD mount lenses, which changed the way of mounting lenses to the more standard approach – rotating the entire lens to attach it to the camera, with a locking button. Red dot to help locate the mounting position, both at the rear and on the barrel of the lens. The aperture cannot be moved or activated unless the lens is mounted to a camera.

West Yorkshire Cameras Nikon SLR Lens


Canon’s autofocus lenses, which all their digital SLR cameras and modern 35mm cameras use. The easiest way to determine the mount is to look at the contacts – they always remain visually identical. The aperture cannot be activated or controlled at all by physical controls on the lens. There is only a switch to control autofocus (and maybe IS). The rear of the lens can be plastic, as in this example, or metal.

West Yorkshire Cameras Nikon SLR Lens


Pentax began with the classic Spotmatic series of cameras, using the ever popular M42 screw mount. The mount is easy and cheap to produce, and present on many cameras, but lacks any advanced features. They later changed to their own Pentax K mount, which has several iterations – the most common being M, A, and their autofocus lenses, F and FA. The latest digital sensor lenses are designated DA, or “Limited” if they are APS-C only. They have successfully kept the ability to use any Pentax Bayonet lens on any Pentax camera, new or old.


M42 screw mount literally screws on and off the camera. The “M42” refers to the size of the thread, as you might with nuts and bolts. Easy to identify, there is usually an aperture pin located on the rear of the mount which will stop the aperture down. The easiest way to identify an M42 lens is to look for a screw thread -there are no bayonet mounts.
West Yorkshire Cameras Nikon SLR Lens

It is worth noting that this is not the same as Leica M39 mount. The M39 mount is smaller and has no aperture pin, as all the lenses are preset.
West Yorkshire Cameras Nikon SLR Lens


The Pentax K bayonet mount started with the M lenses. “M” has come to stand for Manual, as later “A” lenses had an automatic aperture control option – by setting the lens to the A, on the aperture ring.
Visually, there are three bayonet mounting points, on the side of the lens there will be a yellow or white plastic dot, to aid with locating the position of the lens, and a protruding aperture lever from the rear, with a protective plastic part parallel with it.

A PK-M lens will just have an aperture ring with the various values. A PK-A lens will have an A- option next to the smallest aperture, and a small button to engage this. M lenses are usually metal, and A lenses are a little more plastic-oriented.

West Yorkshire Cameras Nikon SLR Lens

West Yorkshire Cameras Nikon SLR Lens

West Yorkshire Cameras Nikon SLR Lens


Minolta has two common mounts – MD and AF. Like the Canon lenses, the older and newer lenses are not compatible with older and newer cameras.
MD are their manual focus lenses, and AF is naturally the autofocus line, which is shared with modern day Sony cameras after Sony bought the Minolta brand and patents (or whatever it was that happened)

They are visually very different – the later autofocus lenses are made of plastic or coated metal, and have no aperture controls on the base of the lens. The manual focus MD lenses are all metal, and have an aperture ring. On the mount, the aperture lever for the AF lenses is present but quite recessed, there are electronic contacts, and a red locating dot. The mount for the MD lenses is very basic, with only an aperture control lever. There is a small notch cut out in a right hand position on one of the three bayonets.

Minolta MD

West Yorkshire Cameras Nikon SLR Lens

Minolta AF

West Yorkshire Cameras Nikon SLR Lens

Olympus OM

This is an easy one. Any OM mount lens will have two rectangular, spring loaded buttons directly opposite-ish each other. That’s the easiest way to visually identify an OM mount lens, as no other lens mount shares this. Any Olympus OM lens fits any Olympus OM camera with no problems.

West Yorkshire Cameras Nikon SLR Lens

Contax / Yashica

Yashica SLR cameras, and Contax 35mm SLR cameras share the same lens mount. Zeiss lenses are intended for Contax cameras, and Yashica lenses are intended for Yashica cameras – but you can mix and match. To identify them visually, it’s a similar situation to Minolta MD lenses – look for the position of the notch cut out of one of the bayonets. On C/Y lenses, it’s on the left of the bayonet.

West Yorkshire Cameras Nikon SLR Lens

Leica R mount

Leica is usually associated with rangefinder cameras, but they also made some damn fine SLR cameras. The lenses are generally compatible across all models, although there are differently ‘cammed’ versions available, and the earliest versions don’t work on the latest cameras (you can read all about it over at Photoethnography.

West Yorkshire Cameras Nikon SLR Lens

Praktica Bayonet PB

Finally, we come to the Praktica bayonet lenses. Fairly common although not that sought after, Zeiss made some optics for these cameras, so are worth using for the price they can be found at. Easy to identify, with just three round electronic contacts in a row, and usually with a ring of plastic in the center. The bodies of the manufacturers lenses are always dark gray plastic.

West Yorkshire Cameras Nikon SLR Lens

Other mounts

Naturally there are other lenses from less popular systems not covered in this guide, and from other size cameras such as medium and large formats. Unusual mount 35mm lenses are fairly uncommon but are out there – these include Mamiya ZE mount, Exakta mount, Sigma SA mount, various proprietary mounts for cameras, such as the Canon EE camera, Nikkorex, Contaflex, etc. If you find anything you can’t identify, you are more than welcome to email us and ask!

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