Behind the lens: the inside story from the developers of the
RF 100-300MM F2.8L IS USM

The RF 100-300MM F2.8L IS USM is Canon's first f/2.8 100-300mm lens. It combines the versatility of a zoom with the focusing speed, sharpness and optical quality of a prime lens, with a fast f/2.8 maximum aperture right across its zoom range and a 5.5-stop optical Image Stabilizer. As a flagship L-series RF lens, it incorporates new technologies and is designed to support the latest camera features including high-speed shooting and enhanced subject detection and tracking. Remarkably, it achieves all of this while being the lightest lens in its class.

So how was this advanced lens designed, what challenges did its creators have to overcome, and what technical advancements were made in producing it?

To find out, we spoke to the designers and developers behind the lens to get the inside story.

What was the goal in developing the RF 100-300MM F2.8L IS USM ?

Yuriyo Asami: Canon's existing EF 300mm f/2.8L IS II USM lens is used in various settings, including sports photography. With the advancements in the Canon EOS R System, we began considering developing an RF lens that could take advantage of the high speed, shallow depth of field and strong compression effects unique to 300mm f/2.8 lenses. This led to the concept of expanding the range of shooting possibilities with an f/2.8 telephoto zoom lens that can be used in all types of photography.

Makoto Hayakawa: We also wanted to respond to the need for a lens with greater focal length than the RF 70-200mm F2.8L IS USM but with a faster aperture than the RF 100-500MM F4.5-7.1 L IS USM. The RF 100-300MM F2.8L IS USM came about as a result of focusing on optical performance rivalling that of a fixed focal length lens in a lightweight, compact package that would allow for mobility.

We used the combination of the EF 300mm f/2.8L IS II USM with an EF-EOS R Mount Adapter as a yardstick for length, weight and image quality. That lens by itself weighs approximately 2.35kg. With this as a starting point, we added 3x zoom, set a target weight of 2.6kg for ease of handling when shooting handheld, and developed technologies one by one.

How did you achieve high image quality for all focal ranges and shooting distances?

Masato Katayose: In terms of optical design, we achieved high image quality from the centre to the periphery of the image by making use of the RF mount's short back focus and placing the lenses near the mount. We used fluorite and doublet UD lenses to reduce the chromatic aberration for each lens group, especially at the telephoto end. We used three UD lenses near the diaphragm, reducing chromatic aberration at the centre of the image

Speaking of mechanical design, can you tell us about the improved autofocus?

Nobuyuki Nagaoka: We used electronic floating focus control with two nano USMs, which have been used in other RF telephoto L-series zoom lenses. Nano USMs have excellent control, are very quiet, and are suitable for shooting both video and stills. I believe we have reached the highest level in terms of AF speed and accuracy, as well as optical performance.

We also implemented an optical design where the drive ranges of the focusing lens and floating lens overlap. As this was an unprecedented design, we did not know whether it was possible at first.

Yumi Toyoda: For electronics/firmware design, we were tasked with creating a control system to avoid clashes between the focusing and floating lenses. To drive lenses using two nano USMs with higher precision, we improved the control algorithm to allow for the control of a complex group of lenses.

And what about image stabilisation?

Nagaoka: The IS unit used in the EF 400mm f/2.8L IS III USM lens was the base for our design. We developed a new actuator optimised for the weight and amount of movement of the moving lens groups – one of the highest levels ever – to responsively control the IS. The RF 100-300MM F2.8L IS USM alone achieves an IS effect of 5.5-stops, with 6-stops of IS possible when combined with In-Body Image Stabilisation (IBIS).

Coordinated control takes advantage of camera developments too, doesn't it?

Toyoda: That is correct. In particular, with the RF mount, the communication speed between the camera body and the lens has been significantly improved and, compared to the EF mount, the amount of information has increased dramatically. Information on focus, zoom, aperture, and lens aberrations as well as IS information are instantly exchanged.

How did you achieve such significant size and weight reductions compared to other super-telephoto zoom lenses?

Nagaoka: The RF 100-300MM F2.8L IS USM features two linear-drive type nano USMs. The nano USMs improve the agility of reciprocating movements, and the mechanical structure of the focus drive has been simplified, which contributes to weight and size reduction.

Katayose: In terms of optical design, by placing three consecutive convex lenses next to the front element, we reduced the diameter of the proceeding lenses as much as possible. We reduced the number of lenses by using large aperture glass moulded (GMo) aspheric lenses. We considered specific gravity in addition to optical characteristics when selecting glass materials, and we worked on reducing the thickness of the concave lenses, which led to improved image quality and a significant weight reduction.

Ken Uraba: In lens processing, we made full use of our expertise, including high-precision processing technology for large aperture aspheric lenses at the Utsunomiya Plant. Improving the surface accuracy of thinned concave lenses to near the processing limit significantly contributed to [both] reducing the weight and improving the image quality.

How does reducing the weight relate to ease of use, robustness and ergonomics?

Asami : Even if we say that the lens is lighter and smaller, I think users understand the difference between numerical weight and how easy the lens is to handle. That is why we took care to create a lens that feels light when holding a camera and is easy to operate.

Masaaki Igarashi :The placement of the lens function/focus preset button was carefully considered for ease of use, to determine the optimal position where the fingertips of the right hand naturally reach.

What new shooting possibilities will all this enable?

Asami: Thanks to the improvements in mobility and portability, we expect photographers to use the lens in press and wildlife photography, and at major sports tournaments.

Hayakawa: The RF 100-300MM F2.8L IS USM can also be used for 140–420mm shooting with the Canon Extender RF 1.4x attached, and for 200–600mm shooting with the Canon Extender RF 2x attached. Being able to use the with extenders will [dramatically] reduce the weight and size of the lens sets that users have to carry, and make it easier for them to move around.

Do you feel you have achieved what you aimed for with this lens?

Asami: I feel like we have created a lens with which professional photographers and high-level amateurs will be happy. I hope that users take the lens in their hands and feel the progress made down to the details, and further expand their range of shooting possibilities.