The single lens reflex camera
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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 l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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 l.jpg
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


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