CANON OPTICAL TECHNOLOGY Vari-Angle Prism (VAP) The VAP In 1992, Canon introduced the world's first vari-angle prism (VAP). At the heart of the VAP are two sheets of glass connected by bellows made of a special film. A liquid with a high index of refraction fills the space between the glass sheets. By slanting the two sheets of glass it is possible to change the angle of refraction of the incoming light, creating blur-free images. A gyro, sensitive to vibrations, detects any shaking of the camera. A microcomputer which controls the VAP then takes over to compensate for the unwanted movements. The non-toxic and non-flammable liquid between the sheets of glass retains its optical clarity over a long period. The bellows are thin, sturdy and impermeable, thus preventing leakage. The VAP was first used in 8 mm camcorders, and has ever since been used for broadcast TV camera lenses and binoculars. Eye-Controlled Auto-Focus Technology Canon was the first to invent and develop eye-controlled auto-focus technology in the world. When the photographer looks through the viewfinder, where the focusing mechanism is located, a beam of infrared light, emitted by a diode, shines on the viewer's eye. This infrared light is reflected by the cornea. This reflected image of the eye passes through a light-gathering lens and is focused on the Base-Stored Image Sensor (BASIS), which determines the eye's line of sight. The image is used to determine the position of the centreof the pupil and the position of the reflected light. From these the angle of rotation of the eye is computed, and with that the sensor can determine exactly where the photographer is looking in the viewfinder. This occurs instantaneously because a microcomputer makes the necessary calculations at an exceptionally high speed. No matter where the subject is located in the viewfinder, it can be focused on by simply looking at it. This technology is utilized in SLR cameras and 8 mm video camcorders. Shift-Method Image Stabilization Technology The image stabilizer (IS) developed by Canon achieves its ends through the lateral shift of a correction lens -- an ideal way to correct blurring caused by an unsteady grip on a single-lens reflex camera. Because the aperture of the front lens is large, it is not possible to use a vari-angle prism in the way one can in an 8 mm camcorder. Nor is it possible to locate it in the optical system, as is done in binoculars, because the lens groups move in the zooming operation. In this IS technology, vibrating gyroscopes detect hand movements. However, optical correction is carried out by a corrective lens group positioned within the zoom optical system. The corrective lens group moves parallel to the image plane following guidance from the hand movement detection signal. As a result, light is refracted in such a way that the effects of any vibration are canceled out, and any blur caused by unsteady hands is automatically corrected. In a telescopic zoom lens with a range of 75 to 300 millimeters, the IS system automatically compensates for hand movements even at low shutter speeds. When photographing at 1/30th of a second, it is possible to achieve an image whose quality compares favorably to one exposed for 1/125th of a second. Aspherical Lens Technology Spherical lenses are subject to a phenomenon known as spherical aberration. As a consequence, it is impossible to focus the light passing through the centre of a lens and the light passing through its periphery on a single point. Spherical aberration can be corrected by combining a series of lens elements; however, if only spherical lenses are used, a large number of elements are needed to achieve the desired result. The solution to the problem is an aspherical lens. This focuses the light passing near the centre of the lens and the light passing through its periphery on a single point. The design of such a lens, the production of the requisite lens dies and the perfection of polishing techniques were technical hurdles which Canon overcame successfully because of its many years of optical expertise. A design which incorporates an aspherical lens needs fewer lens elements and results in more compact units. It also means increased precision as can be seen in Canon steppers used to make ICs, and lightweight products such as compact cameras.