1 / 50

Basic Principles of Imaging and Lenses

Basic Principles of Imaging and Lenses. Light. Electromagnetic Radiation. Light. Photons. These three are the same…. Light pure energy Electromagnetic Waves energy-carrying waves emitted by vibrating electrons Photons particles of light. EM Radiation Travels as a Wave.

opal
Download Presentation

Basic Principles of Imaging and Lenses

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Basic Principles of Imaging and Lenses

  2. Light

  3. Electromagnetic Radiation Light Photons

  4. These three are the same… • Light • pure energy • Electromagnetic Waves • energy-carrying waves emitted by vibrating electrons • Photons • particles of light

  5. EM Radiation Travels as a Wave c = 3 x 108 m/s

  6. EM Radiation Carries Energy • Quantum mechanics tells us that for photons E = hf where E is energy and h is Planck’s constant. • But f = c/l • Putting these equations together, we see that E = hc/l

  7. Electromagnetic Wave Velocity • The speed of light is the same for all seven forms of light. • It is 300,000,000 meters per second or 186,000 miles per second.

  8. The Electromagnetic Spectrum • Radio Waves - communication • Microwaves - used to cook • Infrared - “heat waves” • Visible Light - detected by your eyes • Ultraviolet - causes sunburns • X-rays - penetrates tissue • Gamma Rays - most energetic

  9. The Multi-Wavelength Sun UV Visible X-Ray Composite Radio Infrared

  10. EM Spectrum Relative Sizes

  11. The Visible Spectrum Light waves extend in wavelength from about 400 to 700 nanometers.

  12. Transparent Materials Transparent - the term applied to materials through which light can pass in straight lines.

  13. Opaque Materials Opaque - the term applied to materials that absorb light.

  14. Are clouds transparent or opaque to visible light? • Answer: opaque • Are clouds transparent or opaque to ultraviolet light? • Answer: almost transparent

  15. Special Things About a Light Wave • It does not need a medium through which to travel • It travels with its highest velocity in a vacuum • Its highest velocity is the speed of light, c, equal to 300,000 km/sec • The frequency (or wavelength) of the wave determines whether we call it radio, infrared, visible, ultraviolet, X-ray or gamma-ray.

  16. 1544 A Brief History of Images Camera Obscura, Gemma Frisius, 1558

  17. Camera Obscura "When images of illuminated objects ... penetrate through a small hole into a very dark room ... you will see [on the opposite wall] these objects in their proper form and color, reduced in size ... in a reversed position, owing to the intersection of the rays". Da Vinci Slide credit: David Jacobs

  18. Abu Ali Al-hasen Ibn Alhasen, mathematician, born in Basra, d. 1038 Cairo, claimed he could control the inundations of the Nile, for which caliph Hakim ordered him to Cairo in 1015 or 1017. Realizing his abilities as civil engineer were less than his skill as a mathematician, he feigned insanity to save his head. Until Hakim died in 1021, Alhazen spent his time at the library of Alexandria, writing on geometry, optics, perspective and the camera obscura. Translated into Latin in 1270 and printed as Opticae Thesaurus Alhazani in 1572. MSS at Paris, Oxford, Leyden. An additional MS at the Vatican Library is annotated by Lorenzo Ghiberti of the Florence Baptistry doors (1378 - 1455). Earlier MSS may have existed, for Roger Bacon writes a[bout] optics and the camera obscura before 1266. Alhazen is the first to show how an image is formed on the eye, using the camera obscura as an analog. Alhazen states (in the Latin translation), and with respect to the camera obscura, "Et nos non inventimus ita", we did not invent this. Source: http://www.acmi.net.au/AIC/CAMERA_OBSCURA.html

  19. A Brief History of Images 1558 1568 Lens Based Camera Obscura, 1568

  20. Jetty at Margate England, 1898. http://brightbytes.com/cosite/collection2.html (Jack and Beverly Wilgus) Slide credit: David Jacobs

  21. A Brief History of Images 1558 1568 1837 Still Life, Louis Jaques Mande Daguerre, 1837

  22. A Brief History of Images 1558 1568 1840? Abraham Lincoln?

  23. 1558 A Brief History of Images 1568 1837 Silicon Image Detector, 1970 1970

  24. 1558 A Brief History of Images 1568 1837 1970 Digital Cameras 1995

  25. 1558 A Brief History of Images 1568 1837 1970 Hasselblad HD2-39 1995 2006

  26. Pinhole camera - box with a small hole in it Image is upside down, but not mirrored left-to-right Question: Why does a mirror reverse left-to-right but not top-to-bottom? Pinhole Cameras

  27. image plane y effective focal length, f’ z optical axis pinhole x Pinhole and the Perspective Projection Is an image being formed on the screen? YES! But, not a “clear” one. (x,y) screen scene

  28. Magnification B y d f’ A optical axis z Pinhole A’ d’ x planar scene image plane B’ From perspective projection: Magnification:

  29. Properties of Projection • Points project to points • Lines project to lines • Planes project to the whole or half image • Angles are not preserved • Degenerate cases • Line through focal point projects to a point. • Plane through focal point projects to line

  30. Distant Objects are Smaller Size is inversely proportional to distance. Note that B’ and C’ labels should be switched.

  31. Parallel Lines Meet Common to draw film plane in front of the focal point. Moving the film plane merely scales the image.

  32. Each set of parallel lines meets at a different point The vanishing point for this direction Sets of parallel lines on the same plane lead to collinear vanishing points. The line is called the horizon for that plane Good ways to spot faked images scale and perspective don’t work vanishing points behave badly supermarket tabloids are a great source. Vanishing Points

  33. Problems with Pinholes • Pinhole size (aperture) must be “very small” to obtain a clear image. • However, as pinhole size is made smaller, less light is received by image plane. • If pinhole is comparable to wavelength of incoming light, DIFFRACTION • effects blur the image! • Sharpest image is obtained when: • pinhole diameter • Example: If f’ = 50mm, • = 600nm (red), • d = 0.36mm

  34. The Reason for Lenses

  35. Gaussian Lens Formula: • f is the focal length of the lens – determines the lens’s ability to bend (refract) light • fdifferent from the effective focal length f’ discussed before! Image Formation using (Thin) Lenses • Lenses are used to avoid problems with pinholes. • Ideal Lens: Same projection as pinhole but gathers more light! o i P P’ f

  36. Focus and Defocus aperture aperture diameter Blur Circle, b d Gaussian Law: Blur Circle Diameter : Depth of Field: Range of object distances over which image is sufficiently well focused, i.e., range for which blur circle is less than the resolution of the imaging sensor.

  37. Problems with Lenses Vignetting Compound (Thick) Lens B principal planes A nodal points thickness more light from A than B ! Chromatic Abberation Radial and Tangential Distortion actual ideal ideal actual image plane Lens has different refractive indices for different wavelengths.

  38. Spherical Aberration Spherical lenses are the only easy shape to manufacture, but are not correct for perfect focus.

  39. Two Lens System object final image image plane intermediate virtual image lens 2 lens 1 • Rule : Image formed by first lens is the object for the second lens. • Main Rays : Ray passing through focus emerges parallel to optical axis. • Ray through optical center passes un-deviated. • Magnification: Exercises: What is the combined focal length of the system? What is the combined focal length if d = 0?

  40. Lens systems • A good camera lens may contain 15 elements and cost a many thousand dollars • The best modern lenses may contain aspherical elements

  41. Insect Eye We make cameras that act “similar” to the human eye Fly Mosquito

  42. Human Eye • The eye has an iris like a camera • Focusing is done by changing shape of lens • Retina contains cones (mostly used) and rods (for low light) • The fovea is small region of high resolution containing mostly cones • Optic nerve: 1 million flexible fibers http://www.cas.vanderbilt.edu/bsci111b/eye/human-eye.jpg Slide credit: David Jacobs

  43. Human Eye • Rods • Intensity only • Essentially night vision and peripheral vision only • Since we are trying to fool the center of field of view of human eye (under well lit conditions) we ignore rods

  44. Human Eye • Cones • Three types perceive different portions of the visible light spectrum

  45. Human Eye • Because there are only 3 types of cones in human eyes, we only need 3 stimulus values to fool the human eye • Note: Chickens have 4 types of cones

  46. Human Eye vs. the Camera • We make cameras that act “similar” to the human eye

  47. CCD Cameras http://huizen.ddsw.nl/bewoners/maan/imaging/camera/ccd1.gif Slide credit: David Jacobs

More Related