Glossary |
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| Rear focusing | Focusing is accomplished by moving one or more lens elements positioned internally, behind the lens’ diaphragm assembly. By moving internal elements, less weight is required to be moved, so focusing can be faster and more responsive. Furthermore, the front of the lens does not move during focusing - ideal for photographers who use filters. |
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| Rear Focusing (RF) | With Nikon’s Rear Focusing (RF) system, all the lens elements are divided into specific lens groups, with only the rear lens group moving for focusing. This makes autofocusing operation smoother and faster. |
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| Reduction in overall lens length | To reduce the length of a telephoto lens, it is necessary to increase the mutual power of the convex-concave groupings. Fluorite’s low index of refraction makes it possible to achieve significant reduction in lens length while maintaining high image quality.
Although the extraordinary optical properties of fluorite were discovered in the 19th century and lens designers have long desired to use it, naturally formed pieces of fluorite large enough for use in lens production are extremely difficult to find. Deciding to solve this problem, Canon took up the challenge of developing synthetic crystals, bringing practical fluorite production technology on-line by the late 1960’s. |
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| Reflection | Reflection differs from reflection in that it is a phenomenon which causes a portion of the light striking the surface of glass or other medium to break off and propagate in an entirely new direction. The direction of propagation is the same regardless of wavelength. When light enters and leaves a lens which does not have an anti-reflection coating, approximately 5% of the light is reflected at the glass-air boundary. The amount of light direction of propagation. The two elements of a light wave which can actually be detected by the human eye are the wavelength and amplitude. Differences in wavelength are sensed as differences in color (within the visible light range) and differences in amplitude are sensed as differences in brightness (light intensity). The third element which cannot be detected by the human eye is the direction of vibration within the plane perpendicular to the light wave’s direction of propagation. |
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| Resolution | The resolution of a lens indicates the capacity of reproduction of a subject point of the lens. The resolution of the final photograph depends on three factors: the resolution of the lens, the resolution of the film, and the resolution of the printing paper. Resolution is evaluated by photographing, at a specified magnification, a chart containing groups of black and white stripes that gradually decrease in narrowness, then using a microscope to observe the negative image at a magnification of 50x. It is common to hear resolution expressed as a numerical value such as 50 lines or 100 lines. This value indicates the number of lines per millimeter of the smallest black and white line pattern which can be clearly recorded on the film. To test the resolution of a lens alone, a method is used in which a fine resolution chart is positioned in the location corresponding to the film plane and projected through the test lens onto a screen. The numerical value used for expressing resolving power is only an indication of the degree of resolution possible, and does not indicate resolution clarity or contrast. |
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