This fisheye lens (Photo 1) was developed not only to succeed the EF 15mm f/2.8 fisheye lens but also to provide all Canon EOS Digital cameras with the ultra-high performance expected of an L-type multifunctional fisheye lens. This performance includes genuine fisheye effects, advanced dust and moisture protection, and rugged durability paired with superb picture quality.

In order for fisheye lenses to fit the hemispherical image into the image circle, some part of the picture must be highly compressed. The extent of this compression is closely related to how the image is deformed.

It must be noted that this compression is not the same as severe lens distortion.

(1) Ordinary (non-fisheye) camera lenses

Ordinary camera lenses use central projection methods that map subjects and images so their shapes are similar.

The coefficient between the subject and image sizes is known as magnification. The difference between the lens’s magnification at the periphery and at the center appears in the form of distortion (an aberration). Keeping this lens distortion to a minimum is ideal.

Because this projection method does not allow for any picture compression from the center to the periphery, as the angle of view increases there will always be an area that cannot fit into the picture regardless of how short the focal length is. This is why ordinary lenses cannot take pictures that encompass the entire FOV. The practical limit of this projection method is a focal length of about 14 millimeters and an angle θ of about 57 degrees (full angle of view of 114 degrees) (Figure 1A).

There are many methods of compressing pictures, but for our purposes here I will give the two most common types.

(2) Strong central compression

This method, called stereographic projection, applies heavy compression in the center of the picture, gradually reducing the amount of compression at the periphery.

This method can be used to emphasize the sense of perspective in a scene. It is also used for peephole door lenses and security camera lenses because there is little image deformation at the periphery. The subject’s surface area and size appear much larger at the edges (Figure 1B). One interesting effect with stereographic projections is two cars coming from the left and right will both appear to face the viewer head on.

(3) Moderate peripheral compression

This method, which the EF 8-15mm f/4L Fisheye USM uses, is called equisolid angle projection. An equisolid angle projection applies compression to maintain an almost uniform proportional relationship between image height and the angle of incidence in the center region, and adds slightly more compression at the edges. Although the subject is somewhat squeezed and warped at the edges, it still looks relatively natural in size (Figure 1C).

Photographic fisheye lenses almost exclusively use this projection method because of its modest compression. The EF 8-15mm f/4L Fisheye USM also uses equisolid angle projection.

With these projection methods, the imaging relationship is governed by subject compression. This concept is clearly different from the concept I described earlier - the lens distortion arising from magnification variations in ordinary camera lenses (using central projection). One might say, however, that fisheye lenses produce severe negative lens distortion at the edges if one considers how the subject is emphasized.

The next sections describe the main features of the new fisheye lens.

Our new fisheye lens is a two-stage short-zoom lens constructed with 14 elements in 11 groups. The first stage, consisting of five air-spaced elements, uses a glass-molded aspherical lens for G5 that effectively eliminates spherical, coma, and other optical aberrations. The nine-element, six-group second stage includes a UD lens element that greatly reduces lateral chromatic aberration - a shortcoming of wide-angle lenses - enabling fine resolution detail and high contrast at all magnifications and in all areas of the frame (figures 3 and 4).

We applied our own newly developed special anti-reflective coating, called subwavelength structure coating (SWC), on the highly curved G1R2 surface that is inherent to ultra-wide-angle lenses. SWC stops virtually all reflections even at the edges of the lens. The internal structure of the lens barrel was also optimized using simulation technology to minimize the flare and ghost that occur easily in digital cameras.

The front lens surface (G1R1) is convex and protrudes slightly beyond the lens barrel in order to prevent the lens barrel from blocking light at the edge of the FOV. This means filters cannot be attached to the front of the lens to protect the front element as is common with ordinary lenses. For this reason, the front surface (G1R1) and rearmost lens surface are coated with a fluorine coating, which allows fingerprints and other contaminants to be easily removed. Also for this reason, the lens uses rear drop-in gelatin filters.

This fisheye lens offers faster autofocusing that previous models due to the inner-focusing system mentioned above, a newly developed ring USM, high-speed CPU, and optimized AF algorithms.

Additionally, the lens’s full-time mechanical manual focus construction allows the user to continue focusing manually without leaving the AF mode. Thus, the user can immediately fine-adjust the focus with the focusing ring after initially focusing with AF without touching the focus mode switch. And the zoom limiter lets the user mechanically set the lens to the full-frame fisheye position, marked as “C” on the lens, when using a EOS Digital camera with an APS-C sensor.

Waterproof and dustproof construction at the focus mode switch - which is shaped to prevent the switch from being accidentally moved, the mount, and other switches stop dust and moisture from getting into the lens, making it suitable for taking pictures in harsh conditions.

Because of its very short focal length, this fisheye zoom lens, when stopped down, has an extremely deep depth of field. This means any dirt or fingerprints on the front lens glass (G1R1) will likely show up in the image. When capturing the entire FOV, care must be taken when looking through the viewfinder that the photographer, the lens hood, the tripod, and other items are not in frame. Another problem is that the sun or other intense light sources may unintentionally appear in the FOV and cannot be blocked by the hood. When this happens, the photographer will have to cover the light source or take some other measure to avoid ghost.

When the corners are black, such as when shooting circular fisheye images, the auto-exposure function will still function well most of the time. However, for a higher probability of getting the correct exposure, we recommend that you experiment with the different manual exposures beforehand to get a feel for how the lens responds.

The EF 8-15mm f/4L Fisheye USM brings excellent L-series optical performance and fisheye effects to all EOS Digital cameras. I urge all EOS users to try this lens.