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A burning apparatus consisting of two biconvex lens. A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction.A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis.
Different kinds of camera lenses, including wide angle, telephoto and speciality. A camera lens (also known as photographic lens or photographic objective) is an optical lens or assembly of lenses (compound lens) used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.
Lens hood: used on the end of a lens to block the sun or other light source to prevent glare and lens flare (see also matte box). Lens cap : covers and protects the camera lens when not in use. Lens adapter : allows the use of lenses other than those for which the camera was designed.
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This is any lens with a focal length longer than the diagonal measure of the film or sensor. [121] The most common type of long focus lens is the telephoto lens, a design that uses a special telephoto group to be physically shorter than its focal length. [122] Modern zoom lenses may have some or all of these attributes.
Lenses with focal lengths of 8 to 16 mm may be either rectilinear or fisheye designs. Wide-angle lenses come in both fixed-focal-length and zoom varieties. For 35 mm cameras, lenses producing rectilinear images can be found at focal lengths as short as 8 mm, including zoom lenses with ranges of 2:1 that begin at 12 mm.
The lens aperture is usually specified as an f-number, the ratio of focal length to effective aperture diameter (the diameter of the entrance pupil). A lens typically has a set of marked "f-stops" that the f-number can be set to. A lower f-number denotes a greater aperture which allows more light to reach the film or image sensor.
Near visual acuity or near vision is a measure of how clearly a person can see nearby small objects or letters.Visual acuity in general usually refers clarity of distance vision, and is measured using eye charts like Snellen chart, LogMAR chart etc. Near vision is usually measured and recorded using a printed hand-held card containing different sized paragraphs, words, letters or symbols.