Although the two large-diameter super-telephoto lenses are twins, they were developed from the ground up as replacements for, respectively, the EF 300mm f/2.8L IS USM and the EF 400mm f/2.8L IS USM. The lenses consist of 16 elements in 12 groups. The first lens group, the third lens group, which contains the diaphragm, and the fifth (rear) lens group are stationary, whereas the fourth lens group (IS) compensates for camera shake and the second lens group is the focusing lens group (figures 1 and 2).

The following sections detail the main features of the lenses.

These two lenses are distinguished by the two large-diameter fluorite elements in lens group 1. The purpose of the fluorite elements is to further improve image quality while reducing weight. The previous models had two UD glass elements and one fluorite element to form the achromatic lens group 1. But by using two fluorite elements and optimizing spacing within the lens group, our designers were able to eliminate one element, making the overall optical system lighter, as well as removing more chromatic aberrations than previously. The lenses were also designed to curb color fringing even when mated with the new extenders, thereby delivering high-resolution, high-contrast images at 1.4x or 2x extended telephoto focal lengths (figures 3 and 4).

The lenses provide excellent color balance as well as minimizing flaring and ghost, which commonly occur with digital cameras. This is accomplished by optimizing, using simulation technology, the interior construction of the lens barrel. Ghost is also further reduced with Canon's proprietary SubWavelength Structure Coating (SWC) applied to G12R1. We also treated the front lens (G1R1) and the rear lens (G15R2) which are exposed to the outside air, with a new fluorine coating.

The chromatic aberration improvements described above not only improve the lenses' image quality; they also have the benefit of reducing aberration variations caused by focusing. Pairing these improvements with the introduction of high dispersion glass with extraordinary dispersion characteristics to the focusing lens group shortens the minimum focusing distance to 2.0 meters from 2.5 meters for the EF 300mm f/2.8L IS II USM and to 2.7 meters from 3.0 meters for the EF 400mm f/2.8L IS II USM. This both shortens the minimum focusing distance of the lenses and enhances their tele-macro performance.

Image stabilization on these lenses works by shifting the fourth lens group (elements G10, G11, and G12) perpendicularly to the optical axis to counter camera shake.

The control algorithm has been tuned to suit the IS unit's architecture and characteristics, delivering a stabilization gain equivalent to roughly four f-stops^*1 of shutter speed. The lenses also add a new IS mode (Mode 3) for sports photography to the previous two modes. When Mode 3 is selected and the shutter button pressed halfway, the camera releases the mechanical lock on the IS unit but not the electronic lock. In this way, the camera calculates the amount of image stabilization required but does not actually apply it. When the shutter is fully depressed, the camera releases the electrical lock and the IS unit responses to camera shake based on the running calculations and the exposure controls. This sequence avoids distracting viewfinder image shake while trying to frame the shot. The Mode 2 algorithm has also been revamped to limit viewfinder image shake when recomposing shots or panning. A mechanism that prevents accidental operation when from a tripod makes it possible to shoot with a tripod while leaving image stabilization on. The lenses' image stabilization function is effective against even slight camera shake or other vibrations during tripod shooting.^{*2, *3, *4}

*1. Image stabilization generally reaches its effective limit at a shutter speed of about [1/focal length] seconds.
*2. Image stabilization is effective at shutter speeds between 1/30 of a second and one second.
*3. Image stabilization has no discernable benefit on images taken at shutter speeds slower than one second.
*4. In certain conditions, depending on the tripod type or camera, there may be less blurring in the resulting photograph when the image stabilization function is off.

In addition to reducing the weight of the lens assembly described above, we made bold modifications to the mechanical construction as well. Major components were constructed from magnesium alloy wherever possible. Precision simulations were used to make the lens barrel walls thinner while ensuring they remained sufficiently strong. The thinner walls dramatically reduced the weight of the new models over their predecessors: the EF 300mm f/2.8L IS II USM, including the tripod mount, weighs about 2,350 grams, and the EF 400mm f/2.8L IS II USM weighs in at just 3,850 grams.

The lenses feature the new power focus (PF) mode, which provides smoother focusing movements suitable for movie recording. This mode functions when the focus preset switch is off. In PF mode, rotating the focus recall ring, which is located in front of the focusing ring, smoothly adjusts the focus. The user can select between two focus-shift speeds by the amount the focus recall ring is turned. Applying smooth focusing shifts during a movie can enhance its dramatic or creative appeal.

The lenses' nine-blade electro-magnetic diaphragm unit (EMD) with a circular aperture produces attractive circular bokeh even while focus shifting.

The combination of a ring USM drive, high-speed CPU, and optimized AF algorithm — along with the previously mentioned inner-focusing system — provide the lenses with fast autofocusing performance on par with their predecessors. In addition, the full-time manual focus construction allows the user to continue to focus manually without leaving the AF mode.

The lenses can be used in harsh weather conditions because the rings, switches, and drop-in filter assembly are all sealed to keep water and dust from penetrating inside the lens. Furthermore, the switches have been shaped to prevent accidental movement.

The lenses' design maintains the traditional external appearance and design sense of Canon's super-telephoto series with updates to highlight the luxury and presence befitting Canon's flagship models. These updates include high-grade leather-tone processing, an ergonomic form for a comfortable hold, and a control layout that lets the user concentrate on shooting. Canon's white lenses have also undergone a makeover to reflect an increasing sophistication and refinement, employing a new neutral white coating that is somewhat warmer than the traditional white.^*5

All lens optics use only lead-free glass in consideration of the environment.

A new security lock slot has been provided under the cover of the orientation locking knob. The security lock slot accepts security-wire locks for anti-theft protection.

All accessories included with the lenses (hood, lens strap, lens case, and lens cap) have been completely redesigned for added user convenience and comfort.

*5. The new white coating has been used on all models announced since August 2010.

These two extenders were newly developed as EF lens accessories to replace the EF 1.4x II extender and EF 2x II extender.

The two extenders have been designed — the EF 1.4x III with seven elements in three groups and the EF 2x III with nine elements in five groups (figures 5 and 6) — for maximum optical performance when used in combination with the new super-telephotos — the EF 300mm f/2.8L IS II USM and the EF 400mm f/2.8L IS II USM — announced at the same time. So although the new extenders provide adequate optical performance when used with existing EF lenses, they deliver stunningly fresh images free of color fringing at subject edges when used with the two new models (figures 7, 8, 9, and 10).

Besides applying Canon's Super Spectra coating, a number of design innovations were made to minimize the ghost and flaring that commonly occurs with digital cameras. Precision ghost simulations were used in the development stage to ensure the lens shape and positioning and mechanical construction did not contribute to ghost or flaring.

Only eco-friendly glass was used in the lens optics in consideration of the environment.

The extenders' design took into consideration how they connect with the curved lines of the super-telephoto lens series. At the same time, they were designed for use in harsh weather conditions by completely sealing all contacts, moving parts, mounts, and buttons to keep water and dust from penetrating inside the lens.

A fluorine coating is applied to the outer lens surface so that dust and contamination wipes off easily for easy care and maintenance.

The extenders include a microcontroller to obtain adequate optical performance when used with conventional EF lenses. The microcontroller takes care of communications between the lens and the camera. It sends the master lens's and the extender's ID and other data to the camera, which processes the data to arrive at the precise AF and optimal exposure. The microcontroller also ensures maximum performance when the extenders attached to one of the new super-telephoto lenses.

This month's technical report has presented two new super-telephoto lenses and two new extenders we are confident will address professional photographers' hopes for high performance lenses. We encourage everyone to try out these lenses, and we hope you add them to your camera bag.

These eminently portable Canon lenses that are a pleasure both to use and to carry are sure to add enjoyment and comfort to your photography life.