Behind the Canon RF 85mm F1.2L USM lens: the developers answer 10 questions

Why is the Canon RF 85mm F1.2L USM lens longer than its EF counterpart, the Canon EF 85mm f/1.2L II USM? What's so different about the bokeh? And how can you use this lens to speed up your workflow? 

Here, the Canon lens development team answer these and other burning questions about the Canon RF 85mm F1.2L USM lens and explain how their pursuit of the ideal portrait lens has led to a product that is not only versatile but packed full of features.

We spoke to product planning expert Kaishi Kawai of Canon's Image Communication Business Operations (ICB) Optical Business Group; optical design pro Satoshi Maetaki, manager of Canon's ICB Optical Products Development Center; electrical designer Masami Ichinose, senior engineer at the ICB Optical Products Development Center; mechanical designer Yasushi Murakami of the ICB Optical Products Development Center; and BR Optical Element and DS Coating Design expert Tomohiko Ishibashi of the Optics Technology R&D Center.

Read on to find out why the Canon RF 85mm F1.2L USM lens is the go-to for portrait photographers, and see how it stacks up in comparison to its EF-mount cousin, the Canon EF 85mm f/1.2L II USM lens.

Why did you choose an f/1.2 aperture rather than f/1.4?

Satoshi: "Although one may think there isn't much difference between f/1.2 and f/1.4 when just looking at the numbers, there is nearly a half stop of difference in brightness. Nearly 1.4 times more light is taken in, resulting in a whole new level in terms of design difficulty. A half stop difference may not seem like much, but when designing large aperture lenses such as f/1.2 and f/1.4, this half stop makes a huge difference in terms of difficulty of design."

Kaishi: "The combination of stunning sharpness in the focused areas and the extremely shallow depth of field of f/1.2 delivers unmatched images. Portraits that use the shallow depth of field of f/1.2 have a unique beauty. The widest aperture setting on the RF 85mm F1.2L USM delivers a beautiful bokeh quality not found on other lenses, and amazing resolution, embodying a new type of imaging expression in portrait photography. That is why f/1.2 was chosen."

How is the bokeh different from that of its EF-mount cousin?

Kaishi: "In terms of bokeh, a key point is that the minimum focusing distance is closer than that of the Canon EF 85mm f/1.2L II USM. The strong bokeh created by f/1.2 can be used to create new types of imaging expressions such as close-ups of areas decorated with jewels."

Satoshi: "We try to ensure the bokeh shape stays round at the edge of the frame, and at such a large aperture the lens size needs to be considerably larger. I believe to a certain extent that users can see the improvements to the bokeh shape being cut out in the peripherals [compared to the shape on a DSLR]. That's because there is no mirror box on the Canon EOS R to block the light rays, which is one of the causes of this phenomenon."

Can the bokeh get any creamier?

Tomohiko: "The strong bokeh produced by the large aperture of the Canon RF 85mm F1.2L USM is one feature of the lens. However, lenses with significant chromatic aberration suppression tend to have slightly clearer bokeh contours.

"Some users aren't fond of this clarity in the bokeh, for example when the leaves of a tree overlap in the defocused area. In this regard, we wanted to create a unique lens that delivers smoother bokeh quality, motivating us to start the development of the RF 85mm F1.2L USM DS with Defocus Smoothing (DS) coating. Although its specifications are basically the same as the Canon RF 85mm F1.2L USM, the DS coating will let users enjoy a softer bokeh quality."

How have you included a wide maximum aperture of f/1.2 while keeping colour fringing at bay?

Kaishi: "I sometimes shoot weddings, and I have always felt that colour fringing on white clothing does not represent what people really want in a portrait on such a special day. So with this in mind, we decided to utilise the greater freedom in design made possible by the RF mount."

Tomohiko: The most significant part in reducing chromatic aberration for the Canon RF 85mm F1.2L USM is the BR optical element. This is the second lens to use a BR optical element after the EF 35mm f/1.4L II USM. Canon possesses various optical materials such as fluorite, DO lenses and UD lenses, which correct various types of chromatic aberration, and we select which material is best depending on the optical system of each lens. The BR optical element has extraordinary dispersion properties compared to conventional optical materials, offering sufficient chromatic aberration effects, making it possible to achieve our goal of amazingly high performance. If we didn't have the BR optical element, we would have needed to increase the number of lens elements in the design, making the lens far too large.

Satoshi: "[Also] on this lens, in addition to the usual multilayer coating, Air Sphere Coating (ASC) is used to suppress ghosting and flare."

Is the autofocus up to the L-series lens standard?

Masami: "The Canon RF 85mm F1.2L USM lens uses the same ring-type ultrasonic motor (USM) as on the super telephoto lenses, which has the most powerful torque of any Canon lens, making focusing extremely fast despite the large optics."

Yasushi: "Although the AF drive speed from close-up to infinity is approximately the same as on conventional models, including a focusing range distance selector switch reduces the focusing time during normal shooting, such as portraiture, for more comfortable usage."

Why is the Canon RF 85mm f/1.2L USM longer than its EF mount counterpart?

Satoshi: "In terms of optical design, the total length is measured from the focal plane (the position of the imaging sensor or film). If you compare the EF and RF mounts, the lens mount is closer to the sensor on the RF mount than is the case with the EF mount. Because of this the EF version of some lenses can be shorter as the extra distance is taken up by the longer distance between the lens mount and the sensor in a DSLR camera. This naturally makes the RF version longer in total length to compensate for the difference in sensor-to-mount distance. An easier way to see this is comparing the size of the Canon RF 85mm F1.2L USM by itself and the Canon EF 85mm f/1.2L II USM with the Mount Adapter EF-EOS R attached. The difference is now smaller, and this is the difference you see when you mount the two lenses on the same Canon EOS R camera."

What other custom features are on this lens?

Yasushi: "We added a control ring, which is unique to RF lenses. Just as on the other RF lenses, aperture, shutter speed and other functions can be assigned to the control ring. The control ring was positioned towards the front as on previous RF lenses in consideration of balance during handheld shooting, and considering ease of operation."

How should photographers use this lens to speed up their workflow?

Kaishi: "We recommend that users try assigning exposure compensation to the control ring during portrait shooting. For example, when shooting portraits outdoors and the lighting conditions suddenly change, you can use your left hand to operate the control ring and adjust exposure compensation while simultaneously concentrating on using the shutter button with your right hand."

How durable is the RF 85mm F1.2L USM?

Kaishi: "What we were unwilling to compromise on was the pro specifications of toughness and durability that an L-series lens should have. We want professionals and enthusiasts to be able to hold on to this lens and use it for a long time without worry. The very front and rear of the lens surfaces are coated with fluorine, making maintenance easier than on the Canon EF 85mm f/1.2L II USM. Oil and moisture are repelled, and oil can be easily wiped off with a dry cloth without using solvents."

How sharp is the lens, really?

Kaishi: "When we were developing this lens, many performance tests were carried out repeatedly on a prototype. When shooting at the widest aperture setting using Eye Detection AF in portrait photography, our test photographers spontaneously let out cries of excitement when they saw how sharp the photos were. 

"The Canon RF 85mm F1.2L USM thoroughly suppresses chromatic aberration and delivers photos with high resolution and high contrast in focused areas. We believe the particular appeal of this lens is in its widest aperture setting. We hope that users who have always stopped down a bit during shooting will enjoy the photos that can now be captured when shooting at f/1.2."