Introducing the newly-launched ultra-wide angle zoom lens, the EF11-24mm f/4L USM. How does it achieve both the beautiful image quality typical of an L-lens and an ultra-wide angle of 11mm at its widest end? In this series of articles (4 in total), I will go behind the scenes to find out more about its development. (Reported by: Ryosuke Takahashi)

Developing Canon's largest ever, distortion-eliminating aspherical lenses

- Firstly, I would like to ask about the basic concept behind the development of the EF11-24mm f/4L USM.

Shimada As you can see from the lens' name which includes its focusing distance, the product concept was based on a plan to make it possible for the “world’s widest angle of view" to become a reality. Instead of simply creating a lens with a wide angle of view, we wanted to create a product that could produce a high level of image quality befitting of an L-lens. Additionally, the lens also features the ability to thoroughly suppress distortion that occurs in wide-angle zoom lenses. Using a lens with a wide angle of 11mm presents you with a whole new world that you will have never seen before. It would be great if it could help users achieve new photographic expressions, whether it be a still image or a video.

The building on the right looks as though it were falling towards the centre of the image. The person to the left also appears stretched towards the image edges, with his legs appearing longer than they actually are. These idiosyncratic distortions are typical of the 11mm wide angle lenses.

EOS 5D Mark III/ EF11-24mm f/4L USM/ FL: 11mm/ Aperture-Priority AE (f/8, 1/500 sec)/ ISO 100/ WB: Auto

- If amateur photographers want to try out this lens, which kinds of scenes would it be useful for, and what are some of the characteristics that make it convenient?

Shimada The scenes that can bring out the best in the EF11-24mm f/4L USM can be broadly divided into 4 types. The first is the kind of wide angle image which previously could not be captured within a single shot. The second is the kind that can be captured even from constricted positions where the photographer is unable to move backwards. The third is the kind that makes use of the shortest shooting distance. As it is possible to get as close as 0.32m to the subject when shooting with the 11mm end, you can use this close proximity to the subject to capture bold, wide-macro images. The last type of scene is the kind where the lens' powerful sense of perspective can be utilized to create a surreal-looking image.

- With a focal length of just 11 mm, I believe you must have faced a variety of problems and challenges during its development. What kind of problems did you struggle with in particular and how did you overcome them?

Sakai From an optical perspective, this zoom lens has an unprecedented wide angle of view. The issues we faced developing this product were in achieving high image quality while suppressing lens distortion, and also in coming up with measures to counter ghosting and flaring. To tackle the former, we used the largest aspherical lens element that has ever been used in an interchangeable SLR lens as the first lens element. This is where we introduced the technology of polished aspherical lens elements, something that our company prides itself in. One of the major breakthroughs we have achieved is the ability to mass produce polished aspherical lens elements with a large curvature, as well as with an even larger aperture.

The above is a view of the city from high ground in Avila. Although the shot was taken with the sun in the centre, there is no ghosting and flaring, and the dark areas were also well-moderated. The clouds extending out of the picture might make it look as if it was a video screen capture, but this is actually a depictive ability unique to ultra-wide angle lenses.

EOS 5D Mark III/ EF11-24mm f/4L USM/ FL: 11mm/ Aperture Priority AE (f/8, 1/800 sec, EV+0.3)/ ISO 200/ WB: Auto

- Canon also sells 14mm single focus lenses and 16-35mm wide-angle lenses. Compared to these lenses, is it technically much harder to produce lenses with a focal length of 11mm?

Sakai The changes in the angle of view brought about by widening the wide angle end by 1mm are very different from those brought about by widening the telephoto end by 1mm. There is a tendency to increase the size of the front element in order to take in a wider range. If we were to use traditional glass moulding technology, it would have been difficult to use an aspherical lens for a front element with a diameter this wide, and therefore also impossible to produce high-image quality lenses with low distortion. Not only so, the wider the angle of view, the more sunlight and other artificial light sources entering the lens from all angles, and therefore the higher the tendency for ghosting to occur. We needed to decide on a lens shape and arrangement that would prevent ghosting early on, when we were still at the lens design phase. Even so, there was still some unavoidable ghosting. In order to deal with these problems, we first employed SWC (Subwavelength Structure Coating) in the rear surfaces of the first and second lens. In addition, we also employed ASC (Air Sphere Coating) in the surface of the 4th lens. With these measures, we managed to reduce ghosting substantially and realise a lens performance that satisfies in all aspects.