chapter25 - Chapter 25 Optical Instruments Optical...

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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 Opaque, light-tight box Converging lens Produces a real image Film behind the lens Receives the image
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Digital Camera Image is formed on an electric device CCD Charge- coupled device CMOS Complementary metal-oxide semiconductor Both convert the image into digital form The image can be stored in the camera’s memory
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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 It is a muscular diaphragm that controls pupil size The iris regulates the amount of light entering the eye by dilating the pupil in low light conditions and contracting the pupil in high-light conditions The f-number of the eye is from about 2.8 to 16
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