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| UD glass lenses | Lenses made from fluorite are extremely expensive due to the high cost of synthetic fluorite crystal production. UD (ultra low dispersion) glass made an appearance in the latter half of the 1970’s, delivering a special optical glass which could provide characteristics similar to fluorite but at a lower cost and thereby answering another desire of lens designers. While the index of refraction and dispersion of UD glass are not as low as fluorite, they are significantly lower than other types of optical glass. Moreover, UD glass does display similar partial dispersion characteristics. The selection of the proper lens element combination in consideration of the intended focal length and other factors can provide close to the same effect as fluorite, (two UD lens elements are equivalent to one fluorite element). Super UD glass was introduced in 1993 as a new material that achieves almost the same performance as fluorite while achieving a new balance of cost reduction and higher quality. |
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| USM (Ultrasonic Motor) | Canon became the first camera maker to apply the use of an advanced USM (Ultrasonic Motor) in 1987 when the EF 300mm f/2.8L USM amazed the world with its silent, super-fast autofocus performance. Then, in 1990, Canon developed the lower cost ring-type USM could be used in a variety of more affordable lenses. This feat was followed in 1992 by the development of a new type of micro USM that enabled the automation of production. Every day Canon comes closer to realizing the goal of equipping every EF lens with a USM.
Features of the ring-type USM include its ability to easily achieve the low-speed, high-torque characteristics needed to realize direct drive. Large holding torque means the disc brake automatically holds the lens in place when the motor is stopped. Its construction is extremely simple, operation is virtually noise-free, and it demonstrates excellent start/stop response and control. High efficiency and low power consumption allow the lens to be powered by the camera\'s battery. The motor\'s ring shape is optimally suited to lens barrel applications and its low rotation speed is ideal for lens drive purposes. Rotation speed control covers a wide variable range from 0.2 rpm to 80 rpm to realize high-precision, high-speed lens drive control. Variable-sensitivity electronic manual focus is also available. The broad operating temperature range of -30°C to +60°C (-22°F to 140°F) ensures stable operation even in severe environments. And, all lens drive control is performed by the microprocessor housed within the lens. |
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