Next-generation L-series lenses have evolved to give discerning photographers around the world more of the qualities that they want. At Canon, our proprietary technology has made that progress possible. Beyond special optical element technology, sophisticated optical design and high-precision machining expertise, the keys to opening up a new world of photography lie in our tireless efforts to continue developing ideal lenses for every need.
With lenses that use regular glass, the refractive index varies according to respective wavelengths of various kinds of light. Therefore, the focal points for each of these kinds of light diverge, even if each kind of light should be on the same optical axis. This causes chromatic aberration that appears as color fringing and compromises image quality. To compensate for chromatic aberration, engineers have applied achromatism (color deletion) using combinations of convex and concave lenses, but it has always been difficult for engineers to minimize blue color fringing, due to the highly refractive nature of its short-wavelength color.
Canon took action to eliminate such color bleeding through its design of organic optical materials' molecular structure, and successfully developed the BR optical element featuring extraordinary dispersion characteristics (that largely flex blue light). The BR lens combines this latest element and glass lenses, and controls focal length of blue ray of light. This makes extra-high-level chromatic aberration possible, resulting in excellent image depiction.
The BR lens used for the first time in the EF35mm f/1.4L II USM large-diameter fixed focal length lens contributes to the lens' remarkable image quality worthy of the next-generation L-series lens.
Fluorite, a natural calcium fluoride (CaF2) crystalline mineral, has outstanding optical characteristics including very low refractive index and extraordinary dispersion characteristics that optical glass alone doesn't provide. An optimal combination of optical glass and fluorite elements effectively compensates for residual chromatic aberration (also known as secondary spectrum). Canon successfully produced synthetic fluorite crystals and employed it for photographic lenses in 1969. Fluorite lenses are mainly used by telephoto and super-telephoto lenses of the L-series lineup, attesting to their excellent resolving power.
The EF500mm f/4L IS II USM and EF600mm f/4L IS II USM new-generation L-series lenses typify the excellence of fluorite lenses. Employing two fluorite lens elements (whereas one element was used in the previous models), these lenses make it possible to reduce the number of elements and still provide high image quality with reduced color fringing. The fluorite lens technology helps to reduce lens size and weight, and dramatically improves overall performance.
UD (Ultra-low Dispersion) glass, optical material that Canon developed, exhibits low refractive index, low dispersion, and extraordinary dispersion characteristics. These provide for secondary spectrum elimination effects, all at similar levels to those of fluorite (with the condition that two UD lenses are equivalent to one fluorite lens). In 1993, Canon dramatically improved upon the optical performance of UD lenses and developed Super UD lenses that are nearly as effective as fluorite lenses. This lens technology also greatly helps to reduce aberration and minimize lens sizes.* UD: Ultra Low Dispersion
Spherical lenses had been theoretically limited by their inability to converge parallel rays of light to the same focal point, causing difficulties in the development of spherical aberration compensation for large-aperture lenses, lens distortion compensation for wide-angle lenses, and downsized zoom lenses. Aspherical lenses were the solution to these issues. Canon led aspherical lens manufacturing technology innovation, and in the early 1970s introduced the world's first mass-produced aspherical lenses* featuring dramatically improved delineation.
Canon incorporates very accurate large-aperture aspherica l lenses in its select new-generation L-series lenses. For higher image quality, the EF24-70mm f/2.8L II USM features three (compared to two previously) aspherical lens elements, and the EF11-24mm f/4L USM employs four. For the first group of lens elements, high-precision processing technology was used to develop a ø87mm large-aperture ground aspherical lens that simultaneously achieves both a wide angle of 11mm and high-quality imaging.* Among lenses for use with SLR cameras that do not have a mirror ock-up mechanism.
Anti-reflective Subwavelength Structure Coating (SWC) suppresses light reflection with countless wedge-shaped structures more minute than the wavelength of visible light on the surface of a camera lens. This coating layer enables continuous variation of the refractive index, resulting in full-scale suppression of reflection. SWC realizes excellent anti-reflective effect even with a large angle of incidence, and dramatically reduces flare and ghosting in peripheral areas of the lens, which were difficult to suppress with conventional coatings.
Air Sphere Coating (ASC) technology creates a film containing microspheres of air over a vapor deposition lens coating. Systematic lining of the inside of the coating with spheres of air forms an ultra-low refractive index layer. This results in extreme anti-reflective performance, particularly for incidental light that enters at nearly a vertical angle, effectively preventing flare and ghosting. The layer of air microspheres is covered by an interfacial layer, so the ASC coating is highly durable.* ASC: Air Sphere Coating
This lens coating used in select next-generation L-series lenses helps keep lenses clean by reducing the possibility of dust and dirt adhering to the lens and by facilitating cleaning, should the need arise. It is applied on the tops and bottoms of lens elements that face open air. With outstanding oil- and water-repellent characteristics, this coating makes it easy to wipe dirt from the lens surface with a dry cloth, without requiring lens cleaning solvent. Moreover, static electricity caused by dry wiping is reduced, and the coating's very smooth surface is not easy to scratch. The coating's resistance to drops of water is also beneficial.
The EOS system's high-speed autofocusing is the result of elegant interplay between the camera's AF system and the EF lens internal drive system's control engine. Next-generation L-series lenses feature control CPU and firmware that further enhance this control engine's performance. Moreover, an arithmetic circuit processor added around the CPU disperses the CPU workload, elevating processing capability even more. Adoption of rear focus and inner focus that reduce focusing workload, highly responsive USM, and optimization of the camera's AF algorithm are all seamlessly synchronized for the sake of superior autofocusing speed and precision.