what do the colored rings on canon lenses mean
to identify Canon's lenses
title: Canon EF lens mount text: at the high-end user, most also include environmental or weather sealing and a constant maximum aperture. All L lenses are supplied complete with a hood and a pouch or case, which are not generally included with non-L lenses. Distinctive visual cues include a red ring around the lens and an off-white colour on longer-focal-length models. The latter also helps to reflect light and reduce heat absorption and subsequent internal expansion of lens components that can affect the image quality of long focal length lenses. All L lenses include at least one fluorite or ultra-low-dispersion glass element, and/or certain types of title: Canon FD lens mount text: chromatic aberration at long focal lengths. The earlier versions of these lenses carried "AL", "Aspherical", or "Fluorite" indications on the front of the lens. The post-1979 'New FD' versions acknowledged all the exotic technologies under the single designation "L" (commonly believed to indicate 'luxury' or 'asphericaL'). Canon has continued the "L" designation, and the famous red ring around the lens front, in the current EF autofocus lenses for EOS cameras, where the symbol now officially stands for "Luxury." The FD series included a number of zoom lenses with close-focusing mechanisms, targeted at amateur photographers. The series also included three true title: Canon L lens text: usually have an off-white barrel to reduce heat absorption under the sun that may otherwise affect the performance of the lens, as well as to identify Canon's lenses (for example at sporting events), though these can be confused with Sony A and Pentax K-mount lenses which are also offered in (pure) white. However, shorter focal length L-lenses can be black (such as the Canon EF 24–70 mm f/2.8L) and all L-lens primes under 200 mm are black. L-lenses can be identified by the distinctive red ring on the lens barrel. The off-white colour of the lens barrel is not exclusive title: Canon L lens text: dispersion glass elements. Their front elements do not rotate for the proper operation of some filters, such as circular polarizers. L lenses are often "fast", with maximum apertures commonly 2.8 or 4 and never exceeding 5.6. Standard prime lenses have a much greater maximum aperture, such as Canon's current 50mm and 85mm L lenses which open to 1.2. All current L-series lenses have ultrasonic autofocus motors (USM) and extra communication pins, except for the specialist tilt-shift lenses which do not provide autofocus. Larger sized L-lenses, such as the 70–200 mm, 100–400 mm zooms, and longer focal length primes (300 mm+), title: Canon EF lens mount text: used in some lenses. DO lenses are usually smaller and lighter and are better at handling chromatic aberration, compared to conventional lenses of similar focal length and aperture value. They are more expensive to make. Only the EF 400 mm 4 DO IS USM, its updated Mark II version, and the EF 70–300 mm 4.5–5.6 DO IS USM contain DO elements. DO lenses have a green ring on the barrel. Top range Canon EF lenses are designated "L-series", or "Luxury" lenses. L series lenses are compatible with the full range of EF or EF-S mounts and, as they are aimed