Pekka Buttler, February 2023
Basic Information on the Canon RF mount:
First off, Canon RF is the name for Canon’s new mirrorless interchangeable camera lens mount. The name is – in my opinion – a somewhat unlucky choice as RF in photo circles generally means ‘rangefinder’ (which Canon also used to produce). Moreover, there is considerable risk of confusion between the new RF mount and the earlier (1959–1963) Canon R mount.
Canon has undoubtedly been a major player in the camera industry for more than half a century. Importantly, Canon’s role in the ascendancy of the digital SLR was very pronounced. While Nikon was first to bring a modern dSLR to market, it was Canon who soon grabbed market share, in part thanks to being able to manufacture a series of successful, affordable dSLR cameras (first the D10, later eclipsed by the 300D). Likewise, while Contax (Kyocera) was first to offer a full-frame digital SLR, it was the Canon 1Ds that acted as the reference full-frame dSLR until it was eclipsed by the more affordable Canon 5D – the camera that can be said to have started the full-frame revolution. Similarly Sony was first in introducing a full-frame mirrorless camera, and whether Canon will be able to claw-back from not being first to market remains yet (2023) to be seen.
In any case, Canon introduced its first full frame mirrorless camera – the Canon R – in 2018, in tandem with the Canon RF mount, an initial batch of four lenses and a lineup of adapters for using Canon EF lenses (to bridge the gap while waiting for the Canon RF lens lineup to expand). Since then, Canon has introduced numerous further bodies and lenses, and it seems clear that Canon – while not having formally abandoned the Canon EF mount – is putting all its bets on the Canon RF system.
One more thing. Every camera manufacturer that has introduced a full frame mirrorless mount has also introduced adapters for using the previous generation of lenses, and in this respect Canon was in the fortunate (compare to Nikon or Sony) situation that their entire lineup of previous-mount lenses already communicated electronically. Whereas Sony had to offer a lineup of four different adapters to cover the entire previous generation (including slot-drive AF lenses), Nikon simply did not bother, instead only introducing one adapter that supported only a part of those lenses that Nikon’r pro dSLRs supported.
Not having to bother with such considerations, Canon was free to go in another direction. Not only did Canon introduce an EF to RF adapter that manages to cover every Canon EF lens ever introduced, they also two more adapters: One which adds a programmable control ring, and another that allows the use of drop-in filters (variable ND, Polarizing).
Canon RF mount specifications
Mount type: Bayonet mount (lens release on camera)
Flange focal distance: 20,00 mm
Sensor sizes:
• 36,0 mm x 24,0 mm (‘Full frame’)
• 22,3 mm x 14,8 mm (APS-C) 1
Mount communication:
• 12 electronic contacts (in two adjacent, tiered groups of 8 and 4), spring-loaded at the camera-end.
• 100% electronic communication
Adapting to Canon RF bodies
Being a modern mirrorless full frame camera, there are only very few limitations on what can be adapted to Canon RF cameras.
That said, there are a number of considerations:
• If the lens is dependent on electronic communications, a suitable smart adapter must be available. As already mentioned, such adapters exist for Canon EF lenses. Whether the future will see the introduction of – say – smart adapters for Sony A / Minolta A or Mamiya Z mount lenses is anyone’s guess.
• Adapter availability. While the Canon RF mount has been around for some years, that is not enough to guarantee a wide availability of adapters. Moreover, as Canon seems to be more than a bit hostile towards using anything other than Canon lenses on the RF system, it is not impossible that this will place limits on adapter availability.
• Being among the longer full-frame mirrorless lens mounts, there are a number of systems that will remain challenging for the Canon RF system (Especially Sony FE and Nikon Z).
• Canon RF cameras do not natively support smaller capture areas than APS-C, so it would make things more straightforward (less hassle in post) if the lens was able to project at least an APS-C image circle. Many of those lenses designed for film formats smaller than APS-C (including Pentax-110, C-mount, Olympus PEN-F) regularly cover the APS-C sensor (some even make a good try of full-frame), but this is by no means a given. Hence, it becomes a lens-to-lens question instead of a strictly mount-related issue.
Adapting Canon RF lenses
Canon RF lenses have a rather short flange focal distance, meaning that the list of systems theoretically (optically) able to utilise Canon RF lenses is very short (Fujifilm X, Hasselblad XCD, Nikon Z, Sony FE,). Moreover, as the Canon RF system is highly dependant on the lenses being able to communicate electronically, any adapter would need to be a smart adapter to not entirely cripple the lenses.
Currently it seems no such adapters yet exist, making Canon RF lenses usable only on Canon R cameras.
Footnotes:
1 Canon’s understanding of APS-C has always been a bit more narrow than most of its competitors (Canon has been using smaller sensors), leading to that Canon’s APS-C cameras have generally had a crop factor of 1,6 x (instead of the industry-standard 1,52–1,55 x).