Canon EF 400mm f4.0 DO IS Lens, With Canon 1-Year USA Warranty

The EF 400mm f/4 DO IS USM with 'Multi-Layer Diffractive Optical Element' incorporating beneficial light diffraction, is a major breakthrough in lens design. By incorporating this element in the optical design, the EF 400mm f/4 DO IS USM is much smaller and lighter than a comparable lens having conventional optical elements, yet delivers exceptional image quality.

Canon has a rich history in the development of optical technologies and examples are the use of fluorite and aspherical elements in lens design. These optical elements are now found in diverse range of lens products such as interchangeable SLR lenses, video camera lenses, and digital camera lenses. The Multi-Layer Diffractive Optical Element developed by Canon is a milestone in lens design possessing the characteristics of both fluorite and aspherical elements, which has led to the production of the high-performance EF 400mm f/4 DO IS USM.

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. However, this increases chromatic aberration. To resolve this problem, the Multi-Layer Diffractive Optical Element is incorporated in the lens design to cancel out the chromatic aberration. Compared to a comparable super telephoto lens with a conventional optical design, the EF 400mm f/4 DO IS USM is about 26 percent shorter at 233 mm and about 36 percent lighter at 1,930grams (including the 140gram tripod collar).

DO elements have a diffraction grating that alters the light path by diffraction*1. Such elements are already incorporated in industrial instruments such as spectroscopes and in signal-reading optical systems in CD and DVD players. Natural (white) light's tendency to produce superfluous diffracted light after entering the lens results in flare, which degrades the image quality and therefore have not been employed in camera lenses. By combining a Multi-Layer Diffractive Optical Element and refractive optical element in an optical system, chromatic aberration (color smearing) that adversely affects the image quality can be corrected even more effectively than with a Fluorite element. Also, by adjusting the pitch (spacing) of the diffraction grating the same optical characteristics as a Ground and Polished Aspherical surface can also be achieved. This effectively corrects for Spherical and other aberrations.

The lens also incorporates Canon's unique dust and moisture resistant design. Weatherproof seals are placed on the lens mount and switch panels to repel dust and moisture penetrating the lens. This design enables the lens to be used in conditions that would be considered to harsh for a conventional lens to be used.

The EF 400mm DO IS USM also uses Canon's Image Stabilizer technology that detects camera shake and corrects for it optically. The systems delivers the equivalent of two stops of image shake correction, that makes it possible to hand hold the lens at two stops slower than would normally be possible without camera shake.