1、1,Chapter 40 Mirrors and Lenses,2,40-1 Image formation by mirrors and lenses,1. Geometrical vs. Wave optics,Geometrical optics: The light travel in straight line paths or rays.a /1,Wave optics (physical optics): diffraction.a ,3,2. The formation of image,When the light incident on an objector,Reflec
2、tion (bounces) Mirrors See it,Refraction (bends) Lenses,Often some of each are composed.,4,Light rays from sun bounce off object and go in all directions. Some hit your eyes.,We know objects location by where rays come from.,Color is because some light is absorbed by object before bouncing off.,5,Vi
3、rtual image: (p913),Real image: (p914),A interesting experiment: (p914),6,40-2 Plane Mirrors,All you see is rays that reached your eyes. objects location is where rays appear to come from All needed to do are drawing the lines of rays down,7,Can you see Fidos tail in mirror?,No!,You need light rays
4、from the tail to bounce off mirror and reach your eye!,8,The image of an extended object,Image reversal,Two mirrors,How many images of money will you see (not including the actual money)?,9,40-3 Spherical Mirrors,1. The mirror equation,paraxial ray,focal point,plane mirror,10,2. Sign conventions,R-s
5、ide: real image side; V-side: virtual image side,On the R-side of the mirror, i, r, and f are taken to be positive.,On the V-side of the mirror, i, r, and f are taken to be negative.,The object distance o is positive if the object is real, no matter it is in R-side or V-side.,11,Principal Axis,Rays
6、traveling through focus before hitting mirror are reflected parallel to Principal Axis.,Rays traveling parallel to Principal Axis before hitting mirror are reflected through focus.,3. Ray tracing,12,40-4 Spherical Refracting Surfaces,Refracting surface formula,paraxial ray,13,Sign conventions,14,Sam
7、ple problem 40-5:,Solution: o is positive, r is negative,Then, the image distance i less than object distance o, and the image is virtual.,15,40-5 Thin Lenses,thin lens: the thickness of the lens is small compared with the o, i, and the radii of curvature r1, r2.,Focal point of the thin lens determi
8、ned by geometry and Snells Law: n1 sin(1) = n2 sin(2),Fat in middle = Converging Thin in middle = Diverging Larger n2/n1 more bending, shorter focal length,16,Lens makers equation:,For thin lens and paraxial rays,Thin-lens formula,Sign conventions,17,Two-lens systems,Lens 1 creates a real, inverted
9、image of the object.,Lens 2 creates a real, inverted and reduced image of the image from lens 1.,The combination gives a real, upright, enlarged image of the object.,18,All rays go the same length of the optical path ! (Fermats principle),19,40-6 Optical Instruments,Compound microscope,Refracting te
10、lescope,The simple magnifier,20,Amazing Eye,One of first organs to develop. 100 million Receptors 200,000 /mm2 Sensitive to single photon! Candle from 12 miles,21,Astigmatism Curvature of the lens not symmetric in transverse directions slightly cylindrical different focal lengths,22,Optical Aberrati
11、ons,Chromatic aberration Due to dispersion (index of refraction depends on frequency), focal length can be different for different colors.,Spherical aberration Outside the “paraxial limit”, optimal focusing occurs only for a parabolic lens. Spherical lenses look parabolic for narrow field of view.,2
12、3,Hubble space telescope,The HST was launched in 1990; it was discovered that a lens had been ground incorrectly, so all images were blurry! A replacement “contact lens”, COSTAR, was installed in 1993.,(Now, Hubbles instruments have built-in corrective optics, so COSTAR is no longer needed.),24,Aperture of primary mirror: 2.4 m Mass of primary mirror: 828 kg,The photo of M110,25,Homework: P938 P40-5, 9, 10, 11,
