chapter25_PC - Chapter25 OpticalInstruments...

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    Chapter 25 Optical Instruments
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    Optical Instruments Analysis generally involves the laws of  reflection and refraction Analysis uses the procedures of  geometric optics To explain certain phenomena, the  wave nature of light must be used
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    The Camera The single-lens  photographic camera is  an optical instrument  Components Light-tight box Converging lens Produces a real image Film behind the lens Receives the image
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    Camera Operation Proper focusing leads to sharp images The lens-to-film distance will depend on the object  distance and on the focal length of the lens The shutter is a mechanical device that is  opened for selected time intervals Most cameras have an aperture of adjustable  diameter to further control the intensity of the  light reaching the film With a small-diameter aperture, only light from the  central portion reaches the film, and spherical  aberration is minimized
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    Camera Operation, Intensity Light intensity is a measure of the rate at  which energy is received by the film per unit  area of the image The intensity of the light reaching the film is  proportional to the area of the lens The brightness of the image formed on the  film depends on the light intensity Depends on both the focal length and the diameter  of the lens
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    Camera, f-numbers The ƒ-number of a camera is the ratio of  the focal length of the lens to its  diameter ƒ-number = f/D The ƒ-number is often given as a  description of the lens “speed” A lens with a low f-number is a “fast” lens
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    Camera, f-numbers, cont Increasing the setting from one ƒ-number to the  next higher value decreases the area of the  aperture by a factor of 2 The lowest ƒ-number setting on a camera  corresponds to the aperture wide open and the  maximum possible lens area in use Simple cameras usually have a fixed focal length  and a fixed aperture size, with an ƒ-number of  about 11 Most cameras with variable ƒ-numbers adjust  them automatically
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    The Eye The normal eye focuses  light and produces a  sharp image Essential parts of the  eye Cornea – light passes  through this transparent  structure Aqueous Humor – clear  liquid behind the cornea
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    The Eye – Parts, cont The pupil A variable aperture  An opening in the iris The crystalline lens Most of the refraction takes place at the  outer surface of the eye Where the cornea is covered with a film of  tears
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    The Eyes – Parts, final The iris is the colored portion of the eye
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chapter25_PC - Chapter25 OpticalInstruments...

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