DO Lenses - RF Lens World - Canon South & Southeast Asia

DO Lenses

The introduction of the EF400mm f/4 DO IS USM lens, in 2001, marked the debut of a new technology that would greatly impact super-telephoto lenses. It is the first lens to incorporate a Diffractive Optical (DO) lens group — a proprietary Canon optical technology that allows the size and weight of the 400mm f/4 lens to be reduced, while maintaining the same high performance.

Light has the feature of bending around the edges of obstacles. This physical phenomenon is called “diffraction”. The diffraction phenomenon is known to appear in photographic lenses, particularly when the lens is set to a small aperture. This phenomenon usually degrades image quality. However, Canon discovered a way to take advantage of this feature of light, with the DO lens. The direction of light is regulated using an extremely fine, saw-tooth-shaped grid on the surface of the lens that is aligned in concentric circles. This structure is effective in correcting chromatic aberration.

While general refractive lenses create images that split the spectrum in the order of blue > green > red, DO lenses do the exact opposite, forming images that refract the spectrum in the order of red > green > blue. By combining these two types of lenses, it is possible to cancel and correct chromatic aberration. Furthermore, this makes it possible to reduce the overall length and weight of the lens significantly, compared to conventional optical system designs that use only refractive lenses. This is a triumph of flexible thinking, whereby Canon leveraged the “negative” characteristics of diffraction in order to achieve a technological breakthrough.

DO lenses have evolved further, and the technology has been incorporated in the RF lens lineup: the RF600mm f/11 IS STM and RF800mm f/11 IS STM use a gapless double-layer Diffractive Optical element. The cost has also been reduced, thanks to the development of a special resin material to provide the adhesion between layers.