Canon today announced a prototype Canon EF 400mm f/4 DO IS USM lens, the prototype will be shown at Photokina 2000 (which we will attend) in Cologne, Germany, from Sept 20 - 25. A full commercial version of the lens should be available in the first half of 2001. Diffractive optical elements use a diffraction grating to alter the light path, this new 400mm lens is significantly smaller and lighter (almost 1 KG) than Canon's current 400mm f/4

Multi-Layer Diffractive Optical Element (right)
and Prototype "EF400mm f/4 DO IS USM" (left)

Canon press release:

Canon Develops World's First Multi-layer Diffractive Optical Element for Camera Lenses

Prototype Super Telephoto Lens to be Featured At Photokina 2000

LAKE SUCCESS, N.Y.--(BUSINESS WIRE)--Sept. 6, 2000--Canon U.S.A., the company whose imaging solutions give people Know How, today announced the development of the world's first "Multi-Layer Diffractive Optical Element'' for camera lenses.

A prototype Canon EF 400mm f/4 DO IS USM lens incorporating this element will be exhibited at Photokina 2000 in Cologne, Germany, from Sept. 20-25. A commercial version of this lens will be marketed during the first half of 2001.

Multi-Layer Diffractive Optical Element Multi-Layer Diffractive Optical Element
(Conceptual Diagram)

Canon's history of advanced optical element development includes the creation of fluorite and aspherical elements, which have contributed to the realization of high-performance camera lenses. These optical elements are now found in a diverse range of lens products, such as interchangeable SLR camera lenses, and lenses for video camcorders and digital cameras. Canon's Multi-Layer Diffractive Optical Element, a major innovation in the world of optical technology, represents a milestone in that it possesses the characteristics of both fluorite and aspherical elements.

Diffraction Properties of a Single-Layer Diffractive Optical Element and
Multi-Layer Diffractive Optical Element

Diffractive optical elements have a diffraction grating that alters the path light travels through diffraction.(a) Such elements are already incorporated in such industrial instruments as spectroscopes and in signal-reading optical systems found in CD and DVD players. Diffractive optical elements, however, have not been employed in camera lenses due to the tendency of natural (white) light to produce superfluous diffracted light upon entering the lens, resulting in flare that degrades image quality.

Canon's Multi-Layer Diffractive Optical Element features a multi-layer construction comprising two single-layer diffractive optical elements with opposing concentric circular diffraction gratings. When incident light enters the Multi-Layer Diffractive Optical Element, superfluous diffracted light is not produced and almost all of the light is used for the image. The achievement makes possible for the first time the incorporation of a diffractive optical element in a camera lens.

The most significant characteristic of the diffractive optical element is that the positions where the wavelengths combine to form an image are reversed from those of a refractive optical element. By combining a Multi-Layer Diffractive Optical Element and a refractive optical element within the same optical system, chromatic aberration (color smearing), which adversely affects image quality, can be corrected even more effectively than with a fluorite element. Also, by adjusting the pitch (spacing) of the diffraction grating, the diffractive optical element makes possible the same optical characteristics as a ground and polished aspherical surface, which effectively corrects for spherical and other aberrations.

Correction of Chromatic Aberrations by the Multi-Layer Diffractive Optical Element

During the manufacture of the Multi-Layer Diffractive Optical Element's diffraction grating, the height and pitch of the diffraction grating as well as its positioning requires micron-level precision (1 micron equals 1/1000 mm). Such exacting accuracy was made possible through Canon's proprietary three-dimensional ultra-high-precision micro manufacturing technologies and the replicated aspherical lens manufacturing technology used in the production of Canon EF lenses. Such advanced technology also makes possible the manufacture of the ultra-precision diffractive optical element.

Canon will continue its research and development efforts with the aim of incorporating the Multi-Layer Diffractive Optical Element in a variety of products, such as interchangeable SLR camera lenses, digital camera lenses, HMDs (Head-Mounted Displays),(b) LCD projector lenses, and other imaging equipment.

Overview of the Prototype Canon EF 400mm f/4 DO IS USM Lens

EF400mm f/4 DO IS USM" built in Multi-Layer Diffractive Optical Element (above)
and 400mm f/4 Lens incorporating only refractive optical elements (below)

The Multi-Layer Diffractive Optical Element is effective in correcting chromatic aberrations and, accordingly, should serve well in super telephoto lenses, in which chromatic aberrations are most prone to occur. As an initial trial application, the element has been strategically placed in the prototype EF 400mm f/4 DO IS USM lens. This lens achieves the same high level of image quality as that of comparable super telephoto lenses incorporating only refractive optical elements. The EF 400mm f/4 DO IS USM lens, however, is much smaller and lighter than the other lenses.

Downsizing and Weight Reduction

To make a lens smaller and lighter, the spacing between the elements is shortened and the refractive properties of the front and rear lens groups are made more pronounced. This, however, results in increased chromatic aberration. To resolve this problem, the Multi-Layer Diffractive Optical Element is located within the lens to cancel out the occurrence of chromatic aberration. Compared with conventional super telephoto lenses, the prototype EF 400mm f/4 DO IS USM lens, measuring 233 mm in length, is about 26% shorter and, weighing 1,930 grams (including the 140 gram tripod collar), about 36% lighter.

High Image Quality

The Multi-Layer Diffractive Optical Element placed in the front lens group eliminates chromatic aberration caused by the refractive lens group. Chromatic aberration is thereby suppressed to an absolute minimum. Furthermore, the aspherical effect corrects for spherical and other aberrations, resulting in high resolution and high contrast for outstanding image quality.

Optical downsizing with the Multi-Layer Diffractive Optical Element

Lens downsizing and Weight Reduction with Multi-Layer Diffractive Optical Element