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iam11_lecture04

iam11_lecture04 - Image Acquisition Methods Simon Setzer...

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Image Acquisition Methods Simon Setzer, Lecture 4 Lecture 4: Optics, Sensorics, Photography Imaging by Visible Light II Contents 1. Lens Optics 2. Camera Models 3. Measuring Light 4. Image Sensorics 5. Photographic Parameters 6. Sources of Image Degradation in Visible Light Photography c 2005-2011 M. Welk, J. Weickert, A. Bruhn, O. Vogel and S. Setzer 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Lens Optics (1) Lens Optics Lenses and Lens Models Idea: Lenses bend light beams by refraction (air/glass/air transition). Convex lenses bundle parallel beams such that they become convergent. Concave lenses create divergent beams. Convex-concave lenses allow to shift point of convergence (e.g. glasses). Different lens types: biconvex, plan-convex,biconcave, plan-concave, convex-concave. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

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Lens Optics (2) Ideal Convex Lens Refraction of Different Beams Beams parallel to optical axis converge after refraction to focal point F at distance f ( focal length ). from lens on optical axis ( 1, 2 ). Beams through center C of lens are not bent ( 6 ). Beams diverging from point - 2 F at double focal length before lens converge after refraction to +2 F at double focal length behind lens ( 3, 4 ). Beams diverging from point - F at focal length before lens leave lens parallel to optical axis ( 5 ). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Lens Optics (3) Image Formation by Convex Lenses Image Formation: Light beams from object points converge to image points, or appear to diverge from them after passing the lens. Real Image: image behind the lens (reached by the light beams) Virtual Image: image before the lens (not reached by the light beams) Ideal Lens Formula: Given an ideal convex lens with focal length f , an object point at distance s from the lens and h from the axis (upward) is transferred to an image point at distance s from the lens and h from the axis (downward): 1 f = 1 s + 1 s , h s = h s . s > 0 indicates an upside-down real image s < 0 indicates an upright virtual image 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
Lens Optics (4) Real and Virtual Images Real Image (with s> 2 f ) Real Image (with f <s< 2 f ) Virtual image (with s<f ) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Lens Optics (5) Aberrations Problem: Real lenses do not behave exactly like ideal ones. The different discrepancies are called aberrations . The two main problems are: Spherical Aberration: Bispherical convex lenses only work ideally for beams close to the axis. For beams more distant from the axis, the focal length varies. Remedy: more expensive aspherical lenses . Chromatic Aberration: Dispersion leads to different focal lengths for different wavelengths. Remedy: acromats (lense combinations with different dispersion) Left: Spherical Abberation. Right: Chromatic Abberation. (Wikipedia).

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