The Single-lens Reflex Camera

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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