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The Single-lens Reflex Camera. A camera consists of a lens, a light-tight box, a shutter, and a sensitized plate or a film Shutter speed refers to how long the shutter is open and the film exposed The amount of light must be controlled to avoid overexposure or underexposure

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the single lens reflex camera
The Single-lens Reflex Camera
  • A camera consists of a lens, a light-tight box, a shutter, and a sensitized plate or a film
  • Shutter speed refers to how long the shutter is open and the film exposed
  • The amount of light must be controlled to avoid overexposure or underexposure
  • To control the exposure, a f-stop or iris diaphragm is placed behind the lens
  • The f-stop = f / D, where f is focal length, D: diameter
  • The faster the shutter speed, or the darker the day, the greater the opening to get proper exposure
  • Depth of field is the range of distance which the circles of confusion will be small enough to allow sharp image
  • A telephoto lens acts like a telescope to magnify images

Physics 25: Optical Instruments - Christopher Chui

the human eye corrective lenses
The Human Eye; Corrective Lenses
  • The human eye consists of the iris, lens, retina…
  • Fovea consists of rods and cones to convert light energy into electrical signals interpreted by the brain
  • Refraction is done at the surface of cornea (n=1.376)
  • Far point is the farthest distance to see object clearly
  • Normal eye has a near point=25 cm, infinite far point
  • Myopia, nearsightedness, focuses on nearby objects; and can be corrected by diverging lens
  • Hyperopia, farsightedness, cannot focus near objects; and can be corrected by converging lens
  • Astigmatism, caused by non-round cornea, blurs image; corrected by cylindrical lens

Physics 25: Optical Instruments - Christopher Chui

magnifying glass converging lens
Magnifying Glass = Converging Lens
  • Magnifying power, M = q’/q = (N/f) + 1
  • Telescope magnifies objects very far away
  • Refracting or Keplerian telescope consists of 2 converging lens at each end. M = q’/q = - fo/fe
  • Reflecting telescope uses a curved mirror as the objective. Real image is recorded on film
  • Some telescopes: Newtonian, Cassegrainian, 200” Hale at Palomar, and 10-m Keck on Mauna Kea
  • Terrestrial telescopeupright image. The Galilean has a diverging lens as eyepiecevirtual upright
  • Spy-glass is longupright image

Physics 25: Optical Instruments - Christopher Chui

compound microscope
Compound Microscope
  • A microscope has an eyepiece and objective
  • The image is real and inverted
  • Lateral magnification, mo = hi/ho = di/do = (L-fe)/do
  • Angular magnification, Me = N/fe
  • Overall magnification, M = Memo = (N/fe)[(L-fe)/do ~ NL/fefo
  • Lens aberrations are deviations from simple theory
  • Rays from the edge of the lens will focus at a different point than those from the centerspherical aberration
  • Circle of least confusion is the place of film
  • Rays from different parts of the lensnoncircular images, which include coma and off-axis astigmatism
  • Curvature of field and distortion are other problems of lens
  • Chromatic aberration also exists

Physics 25: Optical Instruments - Christopher Chui

limits of resolution rayleigh criterion
Limits of Resolution; Rayleigh Criterion
  • Two factors: lens aberration, and diffraction
  • An image point is a diffraction pattern: blurred
  • The central maximum has an angular half width given by q = 1.22 l / DRayleigh Criterion, which states: 2 images are resolvable when the center of the diffraction disk of one is directly over the 1st minimum in the diffraction pattern of the other
  • Resolving power, RP = s = fq = 1.22lf / D
  • Oil-immersion objective, RP = 0.61l / n sin a
  • Numerical aperture (NA) of the lens = n sin a
  • It is NOT possible to resolve details smaller than the wavelength of the radiation being used

Physics 25: Optical Instruments - Christopher Chui

x rays and x ray diffraction
X-Rays and X-Ray Diffraction
  • Roentgen (1895) discovered X-rays (30kV to 150kV)
  • X-rays are EM waves with l = 10-2 nm to 10 nm
  • X-ray diffraction examines atoms and molecules
  • Bragg equation: m l = 2d sin f, m = 1, 2, 3,..
  • Computerized tomography (1970s) was developed
  • Computerized axial tomography (CAT) uses extensive computer enhanced software to reconstruct the cross-sectional images, which help medical professionals to see the inside of a human

Physics 25: Optical Instruments - Christopher Chui