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Right chromatic abberation wikipedia 25 26 27 28 lens

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Unformatted text preview: Left: Spherical Abberation. Right: Chromatic Abberation. (Wikipedia). 25 26 27 28 Lens Optics (6) 12 Multiple-Lens Systems 34 Solution: In general, multiple-lens systems can compensate aberrations and thus approximate much better ideal lens behaviour than single lenses. 56 78 • Objective lenses for cameras therefore mostly consist of 3 to 15 lenses • With so many glass surfaces, however, a special treatment of the surfaces (coating) is needed to avoid dramatic losses of light by reflection • Multiple-lens systems can be designed to allow adjustment of focal length by relative movement of some components zoom lens) 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Camera Models (1) 12 Camera Models 34 Pinhole Camera 56 Idea: Mapping of objects at any distance by projection through a small hole • Simplest camera model (camera obscura) • Diameter of the hole is called aperture • Image is captured on screen/sensor at rear side of camera 78 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Pinhole camera. 25 26 27 28 Camera Models (2) Tradeoff Sharpness vs. Brightness 12 34 Problem: The ideal sharpness is obtained only for zero aperture 56 • Small aperture leads to reduced brightness (less photons) or even diffraction. 78 • For positive aperture, far object points are imaged into discs with (approx.) radius of aperture → blurring almost independent of the object distance. 9 10 • The disc into which an object point is images is called disc of confusion. 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Camera Models (3) Camera with Lens 12 34 Solution: Use camera with lense → sharp images with positive aperture • Requires focussing: defocussed object points appear as disk-shaped spots. • Image quality depends on precise focussing and on the optical quality of the lens. Small aperture helps to suppress aberrations. 56 78 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Left: Camera with lens. Right: Distance-dependent defocussing by camera optics, with approximate discs of confusion for different locations. 23 24 25 26 27 28 Camera Models (4) Basic Classification by Focal Length 12 34 Attention: To obtain natural proportions F should equal the image diagonal. For example, for 24 × 36 mm film the normal focal length is 50 mm. • Shorter focal length: Wide-angle Lens • Longer focal length: Tele Lens 56 78 9 10 11 12 13 14 15 16 17 18 19 20 Motif photographed with different focal lengths. Left to right: 20, 50, 200 mm. (Freier 1992). 21 22 23 24 25 26 27 28 Measuring Light (1) Measuring Light 12 34 Radiometry Definition: Radiometry is the measurement of radiation energy emitted by light sources, received by sensors or received and reflected by surfaces. Energy can either be measured totally, or per surface area, or per solid angle. • Energy is measured in Ws (Watt-second), 1 Ws = 1 J = 1 Nm. • Area is measured in square metres m2. • Solid angle is measured in steradians sr. one steradian is the solid angle cutting out 1 m2 of area from a sphere of 1 m radius (similar as 1 rad is the ang...
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This note was uploaded on 07/09/2013 for the course SC 111 taught by Professor S during the Winter '12 term at Uni Saarland.

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