Canon EF 400mm f/4 DO IS II USM Lens

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. An entirely new optical technology for SLR camera lenses, Multi-Layer Diffractive Optics makes possible a 400mm super-telephoto lens that's about one-third shorter and significantly lighter. 

Diffractive Optics are combined with a small Fluorite element, they permit almost total elimination of chromatic aberrations, and at the same time are able to combat spherical aberrations. Combining portability and easy handling, Image Stabilizer weather-resistant construction, superb optics and incredible AF performance, the 400mm DO IS lens is ideal for photographers who want super-telephoto power along with good lens speed in a handholdable package.

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.

Key Features

- Flourite & UD elements eliminate secondary spectrum chromatic aberration 
- High-diffraction optics provide class-leading low size and weight 
- AF Stop function shuts off autofocus when an obstruction appears 
- Dust & moisture resistance made exceptional by magnesium alloy lens barrel and new rear gasket at lens mount 
- Two-stage image stabilization; dual-axis camera shake correction or vertical axis only (for panning) 
- 3-stage focus limiter 
- Focus preset function allows for returning to a specifically set focus by turning a ring in front of the focus ring 
- Full-time manual focus override