Canon EF Lens Technology

DO - Diffractive Optics

Another world's first in camera lens optical design, Canon introduced new technology in order to build a super telephoto that complements its latest compact film and digital SLR cameras. This cutting-edge technology employs diffractive optical elements that use the principle of diffraction to change the direction of the light wave's path. This revolutionary element has Aspherical characteristics, which help define superior maximum aperture image quality, as well as optical qualities superior to UD-glass to totally correct color fringing.

The Multi-Layer Diffractive Optical Elements exhibit outstanding ability to correct chromatic aberrations (color defects), and are especially effective in super telephoto lens design where these specific types of optical defects are most likely to happen. You can see how well the technology works in your own pictures by examining the straight edges of a subject in your picture. You will see a crisp, clear edge without the telltale, prismatic color fringing that is visible with images shot using inferior optics.

Glass lens elements refract, or bend light waves, as they pass through to form an image. That's simply the naturally occurring physics of light. Canon uses multiple elements and special glass to help keep the waves focused like a pinpoint instead of spreading them into the rainbow of color seen when light passes through a glass prism.

To diffract a lightwave means that the ray goes through a change in direction before passing through the lens. The change in direction is caused by a diffraction grating -- very fine parallel grooves or slits on the surface. Canon found that using a concentric diffraction grating that gets smaller toward the edges -- some as fine as tenths of a micrometer -- solved many of one inherent physical limitations of camera optics. The design also makes it possible to obtain the same effect as an Aspherical lens.

And taking the technology a step beyond, Canon actually uses two single-layer diffractive optical elements whose diffraction gratings are bonded together face-to-face. Since longer wavelengths form an image closer to the lens due to the large diffractive angle, and shorter wavelengths form an image farther from the lens due to the smaller diffractive angle, putting the DO elements with conventional glass optics actually cancels out each other's chromatic aberrations and is exceptionally effective in correcting this optical defect. The diffraction that occurs with Canon's Multi-Layer Diffractive optical elements actually corrects the optical system's chromatic aberrations and improves the image formation performance.

The net result of Canon's DO technology is a lens design with reduced size and weight while offering higher image quality than a comparable focal length lens that incorporates conventional glass optical elements. It means a new generation of high-performance lenses that complement the more compact designs of Canon's latest SLR film and digital cameras.

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