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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.

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Basic Principles of Imaging and Lenses

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

  13. 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". Leonardo da Vinci http://www.acmi.net.au/AIC/CAMERA_OBSCURA.html (Russell Naughton) Slide credit: David Jacobs

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

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

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

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

  18. 1558 A Brief History of Images 1568 1837 Silicon Image Detector, 1970 1970

  19. 1558 A Brief History of Images 1568 1837 1970 Digital Cameras 1995

  20. 1558 A Brief History of Images 1568 1837 1970 Hasselblad HD2-39 1995 2006

  21. Geometric Optics and Image Formation

  22. 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

  23. 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

  24. 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

  25. The Reason for Lenses

  26. 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

  27. 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.

  28. 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.

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

  30. 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?

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

  32. 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

  33. The Eye • The human eye is a camera! • Iris - colored annulus with radial muscles • Pupil - the hole (aperture) whose size is controlled by the iris • What’s the “film”? • photoreceptor cells (rods and cones) in the retina

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

  35. Image Formation Digital Camera Film The Eye

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

  37. The Retina

  38. Light Retina up-close

  39. Two types of light-sensitive receptors Cones cone-shaped less sensitive operate in high light color vision Rods rod-shaped highly sensitive operate at night gray-scale vision © Stephen E. Palmer, 2002

  40. Rod / Cone sensitivity The famous sock-matching problem…

  41. 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

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

  43. 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

  44. Distribution of Rods and Cones Night Sky: why are there more stars off-center? © Stephen E. Palmer, 2002

  45. The Physics of Light Some examples of the spectra of light sources © Stephen E. Palmer, 2002

  46. More Spectra metamers

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