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Products >> All Products In Focus: Key Specifications of RF Lenses- Part20

RF85mm f/1.2L USM: An Ideal Lens Made Possible By the RF Mount

Announced on 8 May 2019, the RF85mm f/1.2L USM is a medium telephoto prime lens that unapologetically packs Canon’s latest optical technologies into one high-performance body. We find out how the increased flexibility of the RF mount made all this possible.

Why you’ll always find an 85mm prime lens in a portrait photographer’s kit

An 85mm prime lens is such a staple for portrait photography that it has almost become synonymous with the term “portrait lens”. This is so for two main reasons. 

Firstly, the 85mm angle-of-view presents the shape and dimensionality of a subject in a way that is very similar to what you see with the naked eye. 

Secondly, it also allows a shooting distance that is just right for headshots and chest-up shots: The photographer is neither too near or too far away from the person he/she is photographing, making easy to communicate without feeling too intrusive.

These qualities are further enhanced with a maximum aperture of f/1.2, which provides a very shallow depth-of-field, making it possible to create a very creamy background bokeh that makes the portrait subject stand out well.


Reaching new heights in portrait photography: Building on the strengths of the RF mount

While many other lens manufacturers also produce 85mm prime lenses, very few of these have an aperture as wide as f/1.2. This reflects the difficulty of producing a lens with these specifications. 

Since the release of the FD85mm f/1.2 S.S.C. in 1976, Canon’s 85mm f/1.2 lenses have been much favoured by professional photographers due to their brightness and high image quality. However, one weakness of these previous lenses was the tendency for purple fringing, a form of chromatic aberration, to appear on the edges of wedding dresses, accessories and other subjects with high contrast, especially when shooting near maximum aperture.

This has been fixed on the RF85mm f/1.2L USM thanks to the large mount diameter and short back focus distance of the RF mount, therefore taking image quality to greater heights.


RF85mm f/1.2L USM

Key specifications
Lens construction: 13 elements in 9 groups
Closest focusing distance: 0.85m
Maximum magnification: 0.12x
No. of aperture blades: 9 (circular blade)
Filter diameter: 82mm
Size: φ103.2 x 117.3mm
Weight: approx. 1,195g


Why f/1.2 and not f/1.4?

“The combination of stunning sharpness in the focused areas and the extremely shallow depth of field of f/1.2 deliver unprecedented imaging expressions. Although the RF50mm f/1.2L USM which went on sale earlier is a very sharp lens, the longer focal length of the RF85mm f/1.2L USM produces stronger bokeh.”

- Kaishi Kawai, Product Planning

Portrait of girl

EOS R/ RF85mm f/1.2 L USM / FL: 85mm/ Manual exposure (f/1.2, 1/80 sec, EV±0)/ ISO 800/ WB: Auto


0.5 aperture stops is a huge difference in terms of optical design difficulty

The difference between f/1.4 and f/1.2 is only 0.5 aperture stops, and results in 1.4 times more light entering the lens. However, in terms of optical design, achieving that much of a difference is not as easy as it seems.

 "In order to obtain the same image quality as a slower lens with a high f-number, more advanced aberration correction is necessary.  A half stop difference may not seem like much, but when designing so-called large-aperture lenses such as f/1.2 and f/1.4, this half stop makes a huge difference in terms of design difficulty.”

 - Satoshi Maetaki, Optical Design

The faster the lens, the more important it is to correct optical aberrations

When light enters a lens, it bends due to refraction, causing aberrations that reduce optical performance. To create a fast lens requires the lens to have a large aperture diameter so that it can take in more light. However, this also mean that more light beams are refracted as they pass along the edge of the lens, making the lens even more prone to aberrations. In order to ensure the same image quality as a slower lens, a faster lens would require more advanced aberration correction to be incorporated into the design. 

Achieving a lens design previously not possible

On the EF mount, achieving the same level of aberration correction would require using more lens elements. This would make the lens body significantly bigger, and also cause the AF speed to slow. The design would be possible on paper, but it would not be realistic as a product. 

The RF mount, on the other hand, didn’t just have a large inner diameter just like the EF mount, it also had short back focus distance, making it possible to place large lens elements very close to the image sensor. This made it possible to achieve a high degree of aberration correction without making the lens too big.


RF85mm f/1.2L USM - Taking aberration correction to a new level 

RF85mm f/1.2L USM night photography

Lack of aberrations

A close-up crop of the neon signs at the centre of the image. High contrast areas like these are prone to purple fringing at maximum aperture, but the RF85mm f/1.2L USM suppresses the aberrations well, resulting in a natural rendering.

Close-up of office lights at image corners

The spot light sources at the corners of the image are usually prone to distortion from coma aberration, but this lens captures their shapes faithfully.

EOS R/ RF85mm f/1.2L USM / FL: 85mm/ Manual exposure (f/1.2, 0.4 sec, EV±0)/ ISO 100/ WB: Auto


Incorporating Canon’s latest technologies such as BR optics and ASC

According to Tomohiko Ishibashi, the developer in charge of the BR Optical Element and DS Coating Design, the use of the Blue Spectrum Refractive (BR) lens element was the most significant factor in reducing chromatic aberration on the RF85mm f/1.2L USM.

In fact, the RF85mm f/1.2L USM is only the second lens to use the BR optics, which made its debut on the EF35mm f/1.4L II USM

"Compared with other optical materials, the BR optical element significantly refracts blue colors (short wavelength spectrum). It has extraordinary dispersion properties compared to conventional optical materials, offering sufficient chromatic aberration effects even on extremely thin lens shapes, making it possible to achieve our goal of amazingly high performance."

 - Tomohiko Ishibashi, BR Optical Element, DS Coating Design

RF85mm f/1.2L USM lens diagram

A: Aspherical lens elements
B: UD lens elements
C: BR lens element
D: ASC (Air Sphere Coating)

Apart from BR lens elements, the RF85mm f/1.2L USM also uses:

- Ground aspherical lens elements, which are made from glass materials that are good for correcting chromatic aberrations but which cannot be used in glass moulded aspherical lenses.
- Air Sphere Coating (ASC), which suppresses ghosting and flaring.


Ring-type USM with a larger ring for faster AF

While the RF85mm f/1.2L USM can be considered compact for the quality that it delivers, its 1195g weight might still raise some eyebrows. While a large part of this is due to the lens elements, another major reason lies in the torque needed to drive the focusing unit.

“The RF85mm f/1.2L USM uses the same ring-type USM as on the super telephoto lenses, which has the most powerful torque at Canon. By modifying the control method, maximum motor torque was also raised, which works to move this heavy focusing unit with high precision.”

- Masami Ichinose, Electrical Design

Chest-up portrait

EOS R/ RF85mm f/1.2 L USM / FL: 85mm/ Manual exposure (f/1.2, 1/400 sec, EV±0)/ ISO 800/ WB: Auto


Tip: When shooting portraits, use the control ring for exposure compensation

The lens developers had one tip for users shooting portraits with the lens: Assign the control ring to adjust exposure compensation.

“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 focusing on using the shutter button with your right hand. This provides flexible adaptation to changes in the environment where pros have no room to fail, and even a 0.1 second difference can change everything.”

- Kaishi Kawai, Product Planning


Coming soon: A variation lens with smoother bokeh quality

With the RF85mm f/1.2L USM, the Canon developers focused on thoroughly removing chromatic aberrations and achieving high visual resolution and sharpness in the in-focus areas. However, a large aperture lens like this can also be designed to prioritise soft, smooth bokeh quality. 

This is why Canon is also developing another variety of this lens: The RF85mm f/1.2L USM DS, which uses a new Defocus Smoothing coating, developed in-house, to provide smoother, creamier bokeh. This model is planned for released within 2019.

RF85mm f/1.2L USM DS

RF85mm f/1.2L USM DS


Find out about the other RF lenses that Canon plans to release in 2019 here:
Canon’s New EOS RP: Start Your Full-Frame Mirrorless Journey Today

To learn more about the four pioneer RF lenses, check out:
Expand Your Range of Shooting Possibilities with the All-New RF Lenses
Lens Impressions: RF24-105mm f/4L IS USM in Street Photography
Lens Impressions: RF50mm f/1.2L USM in Portraits & Street Photography
Lens Impressions: RF28-70mm f/2L USM in Natural Landscapes
Lens Impressions: RF35mm f/1.8 Macro IS STM in Street Photography


Read the full interview with the RF85mm f/1.2L USM lens developers here


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