Diffractive Optics, abbreviated in lens designations as DO, is a process of bonding diffractive coatings to the surfaces of two or more lens elements. The elements are then combined to form a single, multilayer DO element designed to cancel chromatic aberrations at various wavelengths when combined with conventional glass optics. Diffractive Optics results in smaller and shorter telephoto lenses without compromising image quality. For example, the EF 70-300mm f/4.5-5.6 DO IS USM lens is 28% shorter than the EF 70-300mm f/4.5-5.6 IS USM lens.
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