How Canon's RF Mount Design Enables Innovative New Lens Designs

When Canon unveiled its first full-frame camera, the EOS R, in 2018, the company touted its new EOS RF lens mount. While it has the same 54-millimeter diameter as the DSLR EF mount, the RF mount’s flange distance is significantly shorter, shrinking from 44 millimeters to just 20. Canon promised that this would enable bold new lens designs, and the company’s latest lenses show that as well as any of Canon’s 40-plus RF lenses.

The Canon RF 14mm f/1.4L VCM and RF 7-14mm f/2.8-3.5L Fisheye STM are cutting-edge ultra-wide lenses. The RF 14mm f/1.4L VCM is Canon’s fastest ultra-wide lens ever made, while the RF 7-14mm f/2.8-3.5L Fisheye STM breaks new ground with its 190-degree field of view and relatively fast aperture. As Canon told PetaPixel at CP+, these lenses are possible in large part because of the RF mount design.

“Because of the [RF mount’s] large diameter, we can put a BR element near to the sensor. We have flexibility of optical design, so we can get the higher emoji and compact,” said Satoshi Maetaki, General Manager, Top Engineer, Optics Technology Development Div. 1, Optics Technology R&D Center, Imaging Business Operations.

Being able to position lens elements closer to the image sensor is important for any lens, but it is especially beneficial when designing ultra-wide lenses. The closer Canon’s engineers can place the glass to the sensor, the better. It means faster apertures, wider focal lengths, superior image quality, and more user-friendly lens designs.

Although the diameter and flange distance of Canon’s RF mount is not unique among all full-frame mirrorless camera systems — there are mounts with larger diameters and shorter flange distances, for example — the advantage compared to the EF mount is massive.

There are ultimately three big reasons why Canon has been able to break new optical ground with its RF lens designs, both delivering all-new focal length and aperture combinations and expanding previous concepts. For example, the RF 14mm f/1.4L VCM is much faster than the older EF 14mm f/2.8, and the RF 7-14mm f/2.8-3.5L Fisheye STM is faster and wider than the EF 8-15mm f/4L Fisheye USM.

“One [reason] is a lens mount big diameter. I mentioned that. And second is we apply the new actuator for this VCM actuator. So because we can make it smaller. And third, this is more important: We develop many new optical technologies,” explained Maetaki.

The optical technology in question includes improved lens elements and optics that deliver the same or better optical performance in smaller, lighter elements. This goes far beyond just making smaller glass elements, as photographers still expect ever-improving optical quality and faster apertures, which historically requires more glass, not less.

Making a lens better is easy if engineers don’t care about its size and weight. However, Canon and photographers do care about a lens’s size, weight, and, of course, cost. So making a lens sharper, better corrected, and faster, while also making it more compact, requires extremely complex, precisely-machined glass elements, and this is an area where Canon focuses significant resources.

BR optics, for example, took many years of consistent, daily research and development. That is very expensive, and the resulting elements aren’t cheap to make, either. But these BR optics significantly reduce longitudinal chromatic aberrations (LoCA), a bugbear of fast lenses, especially wide-angle ones.

But improved lens designs go beyond just sophisticated, complex glass elements. Autofocus mechanisms matter a lot, too.

“During the EF lens era, we used ring type USM [autofocus]. But it’s not very suitable for video shootings and because ring is diameter fixed, it means the lens size is also fixed. Then this time we adapt VCM. That is very high-quality tool. It means we can move the very heavy, large elements. That’s [part of] why we could develop very fast, very wide-angle lenses,” said Yutaka Nakamura, Assistant Manager, IMG Products Planning Department.

When it comes to Canon’s two new ultra-wide, fast L-series lenses, each of which is unlike anything the company has made before, the company is very proud of its development efforts.

“For example, this RF 14mm f/1.4L VCM, it has very, very high image quality with a very compact size. No compromise in image quality,” Nakamura explained.

As for the RF 7-14mm f/2.8-3.5L Fisheye STM, Canon is especially proud of making this lens wider and faster than its EF-mount predecessor. It also features drop-in filter support, which utilizes the drop-in filters Canon developed for its EF-EOS-R mount adapter back in 2018.

The lens is very good for photo and video, Nakamura added. “That’s what we are most proud of.”

When Canon announced the RF 14mm f/1.4L VCM and RF 7-14mm f/2.8-3.5L Fisheye STM together last month, the company went from having one of the weakest wide-angle lens lineups in the full-frame mirrorless space to arguably the strongest and most versatile in just one day.

In 2024, Canon released the 50mm f/1.2, a very fast, but not especially wide prime. Then the company launched the 35mm f/1.4, 24mm f/1.4, and 20mm f/1.4.

“We expanded wide because it is very important. A lot of users, especially those who take astrophotography seriously, [wanted fast, wide lenses.]”

“Then we develop this to fulfill their demands,” Nakamura said. “As mentioned, RF mount has has advantage for developing fast, wide lenses because of its short back focus and large diameter.”

“We would like to demonstrate our strength in a visible way.”

Next up on the docket, Canon says it wants to continue exploring the concept of affordable, fast, and lightweight lenses with good image quality, akin to the RF 45mm f/1.2 STM the company launched last year for just $459.

“We need to provide such concept lenses,” said Maetaki. “That is very important.”

On the extreme other end of the spectrum, Canon is eyeing the 2028 Summer Olympics in Los Angeles, where thousands of photographers will descend on California, armed with flagship cameras and super-telephoto primes.

“Lenses for professionals should be prepared,” Maetaki concluded.

“We also need to expand the lineup for hybrid shooting. We have launched a lot of primes [for hybrid users], also we need to expand zoom lenses.”

Image credits: Canon