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Products >> All Products In Focus: Key Specifications of RF Lenses- Part2

6 Significant Features of RF Lenses

RF mount and RF lenses don't just build on the strengths of the EF system, they go a step further to reimagine it for the future. What advantages does this bring about to the EOS R system and to imaging? Read on to find out.

RF lens features hero image


From EF to RF: The significance of RF lenses

The first EF lens was released 31 years ago in 1987. Characterised by their large, fully-electronic mounts, EF lenses practically became synonymous with Canon, and their quality can be said to be a benchmark for photographers all around the world, from the era of analogue film cameras all the way till today.

Fast forward 30 years on to 2018. In this era, mirrorless cameras, once thought impossible, are now a reality. Accompanying that is the new RF mount system, all poised and ready to take on the next 30 years.

While it embodies the best of the EF lens system, such as the large mount diameter and the fully electronic mount, the RF mount system brings on some benefits of its own. In that sense, RF lenses don’t just continue the qualities that exemplify Canon, but have also reimagined them to provide new, improved functionality.


#1: Better lens-camera communication

12 mount connection pins, but it's not just about the numbers

RF mount and EF mount side-by-side comparison

RF mount: 12-pin connection
EF mount: 8-pin connection

The RF mount has 12 connection pins, more than the 8 pins on EF lenses, and it is also equipped with an improved transmission protocol. These help to increase the speed and volume of data transmission between the camera body and lens. There is more than enough communication capability for current needs, which suggests that Canon has built the mount to be future-proof.

The Digital Lens Optimizer (DLO) is one feature that has benefitted from the new mount, in at least 2 ways:

1. DLO lens correction data can now be stored in-lens. This data can be instantly transferred to the camera when the RF lens is attached, removing the need to manually download and register lens correction data when using a newly-released lens.

2. The faster lens-camera communication maximises DLO performance. For example, DLO can be used during continuous shooting without affecting continuous shooting speed or the number of shots. 


#2: Large mount diameter

3 out of 4 of the pioneer RF lenses are f/2.0 or faster. How is this possible?

The internal diameter of the RF mount is 54mm, which coincidentally is the same size as on the EF mount. Canon’s developers wanted to create a mount system that would provide not just excellent image quality but also enhanced usability, and apparently, they found that 54mm was the size that would achieve the best results.

Generally, a larger mount diameter allows for a larger aperture diameter. While the RF mount is the same size as the EF mount, its new design allows more freedom in optical design, paving the way for lenses with larger maximum apertures in the RF lens line-up.


Large aperture RF lenses

RF28-70mm f/2L USM, RF50mm f/1.2L USM and RF35mm f/1.8 Macro IS STM


#3: Short flange focal distance

This also implies a short back focus distance. So what are the benefits?

When the space that would have been taken up by a mirror is removed, the distance from the mount to the image sensor (i.e., the flange focal distance) can be made shorter.

illustration of back focus distance

Back focus distance: The distance between the rearmost lens element and the image sensor.
Flange focal distance (Flange back distance): The distance between the mount and the image sensor.

On the EOS R and EOS RP, the flange focal distance is 20mm, less than half of the distance on DSLR cameras. This is even after taking into consideration the need to maintain a sturdy, solid design. 

The shorter flange focal distance means that the rearmost lens element can be placed closer to the sensor. In other words, the back-focus distance (the distance between the rearmost lens element and the image sensor) can be made shorter. This not only enables the camera body to be made more compact, but also allows more flexibility in lens design. What was difficult to do with EF lenses can now be achieved.


The difference in back focus between RF and EF mount cameras

Back focus distance on EOS R and RF lens

EOS R + RF24-105mm f/4L IS USM

Back focus distance on EOS 5D Mark IV and EF lens

EOS 5D Mark IV + EF24-105mm f/4L IS II USM


#4: Dual Sensing IS and Hybrid IS

Providing a sense of security with their powerful image stabilisation capabilities

The conventional in-lens Image Stabilization (IS) system features in-lens gyro sensors that detected and corrects camera shake. Dual Sensing IS incorporates this, and additionally uses information from the image sensor to detect camera shake that conventional IS finds hard to detect. This results in better, more precise image stabilisation.

In addition to Dual Sensing IS, the RF35mm f/1.8 Macro IS STM is also equipped with Hybrid IS. Hybrid IS corrects not only the conventional angular camera shake caused by camera rotation and change of camera angle, but also shift camera shake, which occurs during parallel camera movements such as panning.

Dual Sensing IS system cross-section

Dual Sensing IS
The faster data transmission on the RF mount enables more precise Dual Sensing IS than on EOS M-series cameras.

Hybrid IS system cross-section

A) Angular camera shake
B) Shift camera shake
C) IS Unit
D) In-lens microprocessor
E) Acceleration sensor
F) Vibration gyro

Hybrid IS
Vibration gyros and acceleration sensors detect and correct shift camera shake.


#5: Control ring

Controlling camera settings with your lens

In addition to the focusing ring and zoom ring, RF lenses come with a control ring. This ring works like the aperture ring on manual focus lenses, allowing you to control the designated exposure setting with a simple turn. To do this, go to the Camera Functions tab in the menu, and select “Customize dials”. 

Hand turning RF lens control ring

The control ring can be customised to control exposure settings such as aperture, shutter speed, ISO speed and exposure compensation. 


Read more about the control ring and how it makes shooting easier in:
3 Features on the EOS R That Will Change the Way You Shoot

The control ring on RF lenses and the Mount Adapter EF-EOS R is one feature that has earned praise from many photographers. For examples of how other photographers have used it, check out the following:
EOS R: Gliding Through Fog, Sweat, Smiles and Tears
24 hours in Seoul: 10 Captivating Photos Shot with the EOS R
Hands-On Review: Why the EOS R is a Good Addition to My Travel Photography Kit


#6: Thorough attention to image quality

Maximising the merits of RF lenses

The larger mount diameter (mentioned in #2) and short back focus (in #3) enable RF lenses to be designed for even better image quality. For example, it allows a large lens element to be placed very close to the image sensor, and this helps achieve better corner-to-corner image quality.

The lenses also incorporate special coatings such as Subwavelength Structure Coating (SWC) and Air Sphere Coating (ASC) to reduce flaring and ghosting.

For optimal pairing with the higher-resolution RF lenses, the default Sharpness value in the detailed Picture Style settings have also been updated: It’s “4” on the EOS 5D Mark IV, but “2” on the EOS R and EOS RP.

Backlit natural landscape shot with EOS R

EOS R/ RF28-70mm f/2L USM/ FL: 70mm/ Aperture-priority AE (f/14, 1/320 sec, EV+0.3)/ ISO 200/ WB: Auto

Thanks to the special lens coatings, there is no visible ghosting in this backlit shot.


When it released the EOS RP, Canon also revealed that it would be releasing 6 more RF lenses in the second half of 2019. Here’s a sneak peek:
Canon’s New EOS RP: Start Your Full-Frame Mirrorless Journey Today

Find out more about the characteristics of the 4 pioneer RF lenses in:
Expand Your Range of Shooting Possibilities with the All-New RF Lenses

Wondering which RF lens suits you? Check out the infographic here:
RF Lenses: Which One Suits Me?


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Kazuo Nakahara

Kazuo Nakahara

Born in Hokkaido in 1982, Nakahara turned to photography after working at a chemical manufacturing company. He majored in photography at the Vantan Design Institute and is a lecturer for photography workshops and seminars, in addition to working in commercial photography. He is also a representative of the photography information website studio9.