Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Classical Photography and...

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Transcript of Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Classical Photography and...

  • Slide 1
  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Classical Photography and Geometric Optics Imaging Science Fundamentals
  • Slide 2
  • Chester F. Carlson Center for Imaging Science Typical Imaging Chain for Photography source (sun) object processing image collection (lens) exposure (aperture & shutter) detection (photographic film) camera
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Light Gamma Rays Ultraviolet Rays X Rays Light Infrared (IR) Microwave Radio wave 400 nm 750 nm People detect visible wavelengths as colors; the human eye is sensitive to that particular range of wavelengths. Wavelength
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Sources: Sun vs. light bulb Sun emits many different types of radiation, including X-rays, ultraviolet (UV), optical light, infrared (IR), and radio. Most harmful wavelengths (X-ray, UV) are blocked by the atmosphere. A light bulb -- like the Sun -- emits energy over a broad range of wavelengths; most of its energy comes out in the IR, but a lot comes out in the optical.
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Object Energy from the source interacts with the object to be imaged. Some energy is absorbed, while some energy is reflected or scattered. The wavelengths that are scattered -- i.e., not absorbed -- are the ones which determine the color of the object.
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Collection For a camera to be efficient, the pinhole is replaced by a lens. The lens redirects light rays emanating from the object.
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Refraction Light slows down in materials. Imagine a line of marching Girl Scouts... Direction of travel
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Girl Scouts in the Mud As the marching line steps into the mud, they will slow down, depending on how thick the mud is. Mud
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Wavefronts at Normal Angle of Incidence
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Index of Refraction u Index of Refraction (n) is the ratio between the speed of light in vacuum (c) and the speed of light in the medium (v). n = c/v MediumIndex of Refraction Vacuum 1 (exactly) Air 1.0003 Water 1.33 Glass 1.5 Diamond 2.4
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Girl Scouts in Mud at an Angle u The direction of travel changes when the marching line hits the mud at a non-normal angle.
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Wavefront at Non-Normal Angle of Incidence
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Snells Law u This change in direction is described by Snells Law AIR GLASS AIR GLASS normal
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Trigonometry Review sin( ) = y/r (opp/hyp) cos( ) = x/r (adj/hyp) tan( ) = y/x (opp/adj) Adjacent Side (x) Opposite Side (y) Hypotenuse (r) RULES THAT DEFINE SIN, COS, TAN of an ANGLE:
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Snells Law Snells Law: n 1 sin 1 = n 2 sin 2 11 22 n1n1 n2n2 (Or, if 1 and 2 are small, n 1 1 = n 2 2 )
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Refraction for Different Materials AIR WATER GLASS DIAMOND light
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Flat to Curved Surface A curved surface can be approximated with small straight segments.
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Curved Interface u Concave interface diverges rays. u Convex interface converges rays. Assuming n > n nnn
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Graphical Ray Tracing u A way to analyze optical systems. u Light rays always travel from left to right for analysis purposes. Axis of symmetry Image side (+)Source side(-) Light Rays Lens
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Convex Lens u Positive Lens u Burning Glass u Magnifying lens shorthand In real life Double Convex Plano-Convex Positive Meniscus
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Convex Lens u Image focal point, F, is half the distance to the effective center of curvature of the lens. u Object focal point, F, is exactly the same distance on the object side of the lens. Axis of symmetry Light Rays Lens F F Object side Image side
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Convex Lens u Image focal length, f, is the distance from the lens to the image focal point. u Object focal length, f, is the distance from the lens to the object focal point. F f F f
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Ray Diagrams for a Positive (Convex) Lens (infinity) Object Location Image Type and Location Real, at F F Real, at 2F Real, at (infinity) Virtual 2F < F
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Concave Lens u Negative Lens u Near-sighted corrective lens shorthand In real life Double concave Plano- concave Negative meniscus
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Concave Lens u Image focal point, F, is on the object side u Focal length, f, is negative. Axis of symmetry Light Rays Lens F f
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Ray Diagrams for a Negative (Concave) Lens Rays converging toward F Object Location Image Type and Location Virtual, at (infinity) Approaching the lens from (infinity) Virtual, at F Virtual, between F and the lens (infinity)
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Dispersion u Dispersion - Index of refraction, n, depends on the frequency (wavelength) of light. Dispersion is responsible for the colors produced by a prism: red light bends less within the prism, while blue light bends more.
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Chromatic Aberration u Dispersion results in a lens having different focal points for different wavelengths - this effect is called chromatic aberration. u Results in a halo of colors. u Solution: Use 2 lenses of different shape and material (achromatic doublet). F Red. Object (small dot)Image with chromatic aberration F Blue White light
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Spherical Aberration u All the rays do not bend toward the focal point, resulting in a blurred spot. u Solution: use lenses with aspherical curvature, or use a compound lens. F. Object (small dot)Image with spherical aberration
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Other Aberrations u Coma u Off axis blur which looks like the coma of a comet. u Astigmatism u Different focal lengths for different planes. u Distortion u Images formed out of shape...
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Exposure u Exposure is defined as the total amount of light falling on the film. u Exposure = Illuminance * Time camera Aperture Shutter Lens
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Illuminance u Illuminance is the rate of light falling on a given area (i.e. energy per unit time). u Illuminance is controlled by aperture: a larger aperture brings more light to the focus. Small aperture Large aperture
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Aperture and F number u F# (F number) is often used in photography to describe the aperture. u F# = focal length of the system/diameter of aperture d
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Exposure Time u Exposure time is controlled by the shutter: when closed, the film is not exposed to light. u Exposure time is simply the time interval between opening and closing the shutter. Shutter Closed Shutter Open
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Types of Shutters Simplified Camera Between the Lens (BTL) Or Leaf Shutter Focal Plane Shutter
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  • Imaging Science FundamentalsChester F. Carlson Center for Imaging Science BTL or Leaf Shutter u Made o