Since the first Canon camera came out in 1946, there have been a total of eight (8) different mainstream lens mounts used. Of course, every time, you change major specs on a lens mount, existing lenses cannot be used on the new lens mount, except perhaps by using an appropriate mount adapter, but losing some important features in the process.
Here is a brief history of the various Canon lens mounts from 1946 and culminating to its latest RF mount.
The Screw-type mount with a standard thread type (as used on Leica cameras) was used on Canon’s rangefinder cameras. You basically screwed the lens onto the camera, which took quite a long time to do (@ 6 seconds). It was all mechanical, with the lens barrel mechanically pushing a lever atop the camera-side mount to transmit distance information.
The R mount made its debut in 1959 on the Canon’s first SLR (Single Lens Reflex) camera, the Canonflex, with fully-automatic apertures. The mechanism also featured a built-in driving spring that reset the aperture after capturing an image. The R mount was a spigot mount that allowed the lens to be fixed firmly onto the camera by quickly tightening a ring on the lens. That was much faster than screwing a lens onto the camera and made changing lenses a breeze. Canon also started using fancy naming marketing, calling its new automatic aperture mechanism the “Super-Canomatic System.”
The FL mount was released in 1964 and supported TTL (Through-The-Lens) metering at minimum aperture. This allowed the use on an in-camera exposure meter to measure light entering through the lens, hence the TTL label. It improved upon the R mount in that the aperture was now driven by mechanisms in the camera body itself, hence simplifying the automatic aperture mechanism inside the lens and making smaller lenses possible.
The F-1 SLR (the camera that really launched Canon as a professional camera, though at that time used mostly by professional nature and landscape photographers) used the FD Mount which supported TTL metering at maximum aperture and featured a predecessor of the automatic exposure (AE) mechanism. This meant that you did not need to narrow the aperture (and hence obtain a darker image in the viewfinder) to obtain accurate light metering. The use of various pins and levers on the lens allowed the camera and lens to transmit information to each other. This was also the first time that Canon used a multi-coating on its FD lenses to capture more vibrant colors onto color film.
The New F-1 featured an improved New FD Mount providing improved ease of installation while retaining compatibility with the FD mount. Instead of turning the ring to attach a lens, now the whole lens was turned and locked into position. As a safety feature, a Lock Button was added to the mount.
From 1987 onward:
The EF mount had the distinction of being the world’s first fully electronic mount that would be used in all cameras of all brands from then on. Focusing and aperture setting were fully digitally controlled, with no levers or physical connecting mechanisms between camera and lens. Instead, it relied on a series of electronic connection pins. The mount used a bayonet design which made lens mounting even easier.
Editor’s note: On a personal note, this is where IMHO camera design took a turn for the worse, with the advent of the Mode Dial, Command Dial and buttons which replaced the dedicated Shutter Speed dial, ISO dial, and Aperture ring. Cameras also started to lose its characterful boxy look, replaced by a more “modern” rounded, organic, and shapeless look. Canon, you’re to blame. Also please, don’t repeat the mistakes of 1987: e.g., no M-Fn touchbar, and please keep the LCD completely centered under the viewfinder (I can live with it, but it still drives me nuts that it isn’t).
In 2000, Canon introduced its first DSLR (Digital SLR), the D30, which also used the EF mount but a smaller APS-C sensor. This meant that the EF mount had successfully bridged from the film age into the digital age.
However, mounting a large EF lens (designed for larger full-frame DSLRs) onto the smaller D30 APS-C DSLR defeated the purpose of using a smaller APS-C sensor (for a smaller and lighter camera), so in 2004, Canon released its smaller EF-S lenses which still used the same EF mount but were exclusively designed and meant to work with its APS-C DSLRs.
From 2012 onward:
In 2012, to counter the growing popularity of Panasonic’s and Olympus’ Micro Four Thirds Mirrorless cameras, Canon introduced its first mirrorless camera, the EOS M, which used a smaller APS-C sensor and a smaller EF-M mount. Without the mirror, and with a shorter back focus, EOS M mirrorless cameras could be more compact and lighter than its counterpart DSLR versions (which used the larger EF mount), with smaller and lighter lenses.
Using an appropriate mount adapter, EF and EF-S lenses could also be mounted onto EOS M cameras (which made available lots of quality lenses in all focal lengths combination, though somewhat defeating the purpose of compactness and lightness).
Though the EOS M Series cameras were very well designed and made, Canon chose not to release a lot of EF-M lenses in the focal lengths photographers demanded, hence limiting the popularity and seriousness of its EOS M Series mirrorless system and relegating it to mainly entry-level point-and-shoot photography.
From 2018 onward:
Finally, in 2018, backed into a corner by the surging popularity of Sony’s A7 Series full-frame mirrorless cameras which saw many pro photographers finally abandoning their trusted (but heavy and cumbersome) DSLR systems and increasingly switching to the A7 Series cameras, Canon had no choice but took the plunge into serious mirrorless camera design by unveiling its new EOS R Full-Frame Mirrorless camera using a new RF mount.
The RF mount uses the same 54mm diameter of the EF mount but its shorter back focus enables the design of more compact and lighter full-frame mirrorless cameras (though not necessarily of RF lenses). It’s 12-pin communication system promises faster and higher volume data transfer between lens and camera, enabling better functionality and image quality.
We are now in 2020, and though we have yet to see Canon’s flagship mirrorless camera (comparable to its EOS-1D X Mark III DSLR), the announced EOS R5 would probably rank close behind it.
With the new RF mount and the EOS R Series full-frame mirrorless cameras, Canon has effectively signaled its formal switch from DSLR technology to Mirrorless technology. Though it will continue to design and release DSLRs for a while more, expect a gradual but definite move to everything mirrorless.
If the history of Canon’s lens mounts and cameras have taught us anything, it’s that Canon engineers can really innovate and lead. The announced EOS R5 promises to be a powerhouse of a full-frame mirrorless camera able to hold its own against Sony’s A7 Series. Expect Canon to try and reclaim its top dog status with pro photographers — and wow us all with how a mirrorless camera should really be designed and work.
Source: Canon Camera Museum