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

The developers reveal how they designed and created Canon's most advanced super-telephoto lens yet, combining all the benefits of a zoom with the qualities of an f/2.8 prime.
Four of the developers of the RF 100-300MM F2.8L IS USM sit at a table, one of them holding a camera with the lens attached.

"When designing something completely new, you are bound to come across obstacles, and it makes you think, 'I see; that is why this hasn't been done yet'," says Makoto Hayakawa, Chief of Development/Mechanical Design (centre, holding lens). "With the RF 100-300MM F2.8L IS USM, we achieved the highest level of optical performance, reliability, AF speed and precision in a lightweight package. I think we were able to achieve a reduction in weight without compromising on a single factor."

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.

Seven people, the developers of the Canon RF 100-300MM F2.8L IS USM, stand side by side, with the man in the middle holding a camera fitted with the lens

The developers of Canon's breakthrough RF 100-300MM F2.8L IS USM lens: Yuriyo Asami (Product Planning), Masato Katayose (Optical Design), Nobuyuki Nagaoka (Mechanical Design), Makoto Hayakawa (Chief of Development/Mechanical Design), Yumi Toyoda (Electronics/Firmware Design), Masaaki Igarashi (Design), and Ken Uraba (Manufacturing Technology).

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.

A side view of the RF 100-300MM F2.8L IS USM with the casing made transparent at the mount end to reveal the internal components.

The developers achieved a reduction in size and improvement in image quality through daring innovations in mechanical and optical design. The RF 100-300MM F2.8L IS USM is the first lens with two nano USMs for electronic floating focus control, and the drive ranges of the floating lens and focusing lens overlap – a radical design decision that posed its own challenges.

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

We also used a large aperture glass moulded (GMo) aspheric lens for the final lens group. This was a significant factor in reducing the number of lenses and achieving high image quality. We designed the lens to thoroughly reduce chromatic aberration and preserve the soft bokeh effect of the 300mm f/2.8 lens. In addition, to reduce ghosting, we used Air Sphere Coating (ASC) to achieve a high anti-reflective effect.

Hayakawa: In the mechanical design, we installed a new ball-bearing structure to hold the cam ring of the zoom lens group, which moves backwards and forwards when zooming. The ball-bearing structure suppresses rattling and stabilises the lens position. Thus, even though the RF 100-300MM F2.8L IS USM is a zoom lens, we could ensure optical performance rivaling that of a fixed focal length lens.

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A man holds a design prototype of the RF 100-300MM F2.8L IS USM, with various component prototypes on the table in front of him.

Masaaki Igarashi holds a design prototype of the RF 100-300MM F2.8L IS USM, with various component prototypes on the table in front of him. "The Canon EOS R System is based on the Mount Core Design concept," he explains, which makes the RF Mount the starting point for lens and camera design, but this lens required numerous innovations. For example, he notes, "we designed a new wide-mount core ring for the RF 100-300MM F2.8L IS USM to give it a balanced design when attached to the camera body."

Hands holding part of the RF 100-300MM F2.8L IS USM lens mechanism

"To reduce the weight of the lens, we extensively used magnesium alloys," reveals Ken Uraba. "By using a combination of composite materials, we aimed to create a lightweight structure that was also resistant to vibration and shocks for the internal components."

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.

A cutaway diagram of the RF 100-300MM F2.8L IS USM lens showing its weather sealin

As a Canon L-series lens, the RF 100-300MM F2.8L IS USM features advanced environmental protection, including dust and drip sealing and mechanical shock resistance. It also features Canon's iconic white thermal finish, which helps ensure that the lens stays cool even during long shoots in the sun.

Two of the RF 100-300MM F2.8L IS USM developers sit at a table, with the lens in front of one and part of its mechanism in front of the other.

Optimising the performance of the RF 100-300MM F2.8L IS USM, particularly enhanced image stabilisation, posed challenges for both mechanical and electronics design. "It wasn't easy to create an optimal control algorithm to take advantage of the characteristics of the gyro sensor inside the lens," says Yumi Toyoda. "We were able to realise high-performance IS by coordinating control with the camera throughout the entire zoom range thanks to high-speed communication between the camera body and the lens."

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).

Toyoda: Coordinated IS control has made it possible to accurately detect and correct shaking information across the camera and lens. This is based on the gyro sensors on both the camera and lens, in addition to the camera's acceleration sensor and live view images. To detect low-frequency swaying, such as movement of the entire body when shooting handheld, we gave the RF 100-300MM F2.8L IS USM a design that is more resistant to low-frequency sway.

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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.

A developer holds part of the internal mechanism of the RF 100-300MM F2.8L IS USM while the complete lens, attached to a camera, sits on the table in front of him.

It was a core aim of the optical design to achieve the soft bokeh characteristic of f/2.8 lenses. The nine-blade aperture in the RF 100-300MM F2.8L IS USM renders highlights and out-of-focus areas beautifully, while a moulded glass aspheric lens, unusual in a super telephoto, along with UD and fluorite elements work together to deliver incredible detail with reduced chromatic aberration, ghosting and flare.

A photographer wearing a high-visibility jacket carries a camera with RF 100-300MM F2.8L IS USM attached, slung over one shoulder.

The RF 100-300MM F2.8L IS USM is the lightest lens in its class. With its versatile zoom range, further enhanced by its compatibility with Canon's RF 1.4x and RF 2x extenders, it is designed to give professionals a lightweight all-in solution that's much easier to carry around in the field than a kitbag full of prime lenses to cover the same requirements.

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.

A hand poised alongside the controls on the side of barrel of the RF 100-300MM F2.8L IS USM.

The RF 100-300MM F2.8L IS USM is the first super-telephoto zoom lens to feature the lens control ring that users enjoy on RF prime lenses, which can be customised to control aperture, shutter speed, ISO and exposure compensation. Ergonomics and ease of use were a priority in the design of everything from the placement of buttons and controls to the textures and contours of the casing, ensuring comfortable hold and operation.

A photograph taken with a Canon RF 100-300MM F2.8L IS USM of a table tennis player frozen in motion just after hitting the ball, which is out of focus in the foreground

"By reducing the weight of the focusing lens, we could use nano USM instead of the previous ring USM, which has also enabled faster focus control," explains Toyoda. "In addition, as frame speeds for continuous shooting are also getting faster, we improved the nano USM's drive control algorithms." Taken on a Canon EOS R3 with Canon RF 100-300MM F2.8L IS USM lens at 300mm, 1/4000 sec, f/2.8 and ISO 6400.

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.

A photographer wearing a high-visibility jacket uses a Canon EOS R3 with RF 100-300MM F2.8L IS USM lens attached on a monopod.

"For the RF 100-300MM F2.8L IS USM, we emphasised stability in terms of the centre of gravity and robustness," says Hayakawa. "That's why we decided to make the lens barrel fully fixed. We also adjusted the position of the tripod mount ring so that rather than the support point of the monopod, the centre of gravity is closer to the user's hands when shooting with a monopod."

An action shot taken with a Canon RF 100-300MM F2.8L IS USM of two footballers, one in blue and one in red, clashing as the former kicks the ball away.

"We worked to improve the precision of focus tracking when zooming," Toyoda says. "We improved the alignment method for tracking control so that focus shift is automatically corrected and focus is maintained. As a result, we maintained focus tracking performance across the entire zoom range. Also, as the RF 100-300MM F2.8L IS USM supports focus breathing correction installed on the camera body, it can reduce changes in the angle of view when moving the focus during video shooting." Taken on a Canon EOS R3 with Canon RF 100-300MM F2.8L IS USM lens at 200mm, 1/2700 sec, f/2.8 and ISO 250.

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.

Peter Wolinski & Sarah Bakkland

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