1Lecture 14Chap. 6 – Optical InstrumentsFeb. 25, 2010Homework #6, on ch. 6, due March 4Yes, it is March already, almost. Exam resultsCU Learn will go up this week, hopefullyExam 1 Histogram0102030405060700102030405060708090100MoreFrequency<50 = fail danger, grade range 19 - 98Average on ray tracing part of exam = 12/30Total grade = ray tracing part (30 pts.) + 70 pts. * (scantron/27) 90 - 10080 – 90Lecture plan3Exam II will cover • Ch. 4 (camera), • Ch. 5 (the eye), • Ch. 6 (optical instruments), • Ch. 7 (visual perception),• Ch. 9 & 10 (color & color perception). •We save Ch. 8 for later. 4Optical instruments• Single lens instruments– Eyeglasses– Magnifying glass•Two lens– Telescope & binoculars– Microscope• The projector– Projection lens– Field lens5EyeglassesFor nearsighted people (can’t focus far away)Eyeglasses are diverging (thinner in middle)Normal vision: you can focus from 25 cm to infinity (∞)For farsighted people (can’t focus up close)Eyeglasses are converging (thicker in middle)Demo: eyeglasses6Eyeglass prescription is in dioptersOptometrists use diopters to measure the strength of a lensDiopters [or D] = 1 / (focal length in meters)Example: f = 50 cm or f = 0.5 m D = 1/f = 2 diopters (units are 1/meters)7AstigmatismVertical and horizontal lines focus differently This problem is fixed by a cylinder lensSharply focusedOut of focusFocuses in one direction, but not the other!8Action of a cylinder lensFocuses in one direction, but not the other!If a cylinder lens is needed for your eyeglasses, your cornea and eyelens is curved more in one direction than in the other!Focus is a line, not a pointOne lens magnifier (again)9Demo with video camera10Magnification of a one-lens magnifierMagnification = Example: 5 cm focal length has 5 magnification10 cm focal length has 2.5 magnification2 mm focal length has 125 magnificationcmin length focalcm 2511van Leeuwenhoek’s microscope 25 cm, reading distance, approximatelyFocal length, approximately12van Leeuwenhoek’s microscope Year: 1600sTiny lens with 2 mm focal length(a lens cannot be much bigger than the focal length)Magnification = Problem: image was still small, and very dim. 125cm0.2cm 25=13Robert Hooke’s microscope 1600sDiscovered: Blood cellsMicrobes14Robert Hooke’s two-lens microscope objectlens 1Nosepieceor Objectivelens 2eyepiecelens 1 imagelens 2 imageA magnifying glass (the eyepiece) magnifies the first image further. The first lens, the nosepiece, is used as a projection lens. Demo with video camera15Hooke’s discoveriesThe cellDetails of a flea16Robert Hooke’s two-lens microscopeMagnification = M1x M2Example: Eyepiece M2= 25 Nosepiece M1= 40 Final magnification = 40 x 25 = 1000M1, like for any projection lens, is Xi/ XoM2, like for any magnifier, is 25 cm / focal length17Modern studentbinocular microscopeA beamsplitter, a half-silvered mirror, sends half the light to each eyepiece. 18Galileo’s telescope (~1600)Negative lens for eyepiece gives right-side-up image.19Kepler’s telescope (~1600)Positive lens for eyepiece gives upside down image that is easier to see. lens 1Objectivelens 2eyepiecelens 1 imagelens 2 imageDemo with video camera20Galileo’s telescope30 x magnificationTiny lens means not much light entered, so image is dim.Discoveries: SunspotsCraters on the MoonPhases of VenusMoons of JupiterDemoMagnification of a telescope(refractor or reflector)Magnification = Example: Objective focal length = 1 m = 100 cmEyepiece focal length = 1 cmMagnification = 10021eyepiece oflength focalmirroror lens objective oflength focalUseless magnificationA bigger fuzzy image is not useful (no additional information). A high resolution image requires large lenses and mirrors. 228 inch reflector telescope Hubble telescope, 96 inch mirrorSmallest visible feature ∝ 1/(diameter of lens or mirror)23Yerkes observatory,Largest refractor40 inch lens1897Larger lenses would sag under their own weight. The lens was achromatic (two kinds of glass). 24Newton’s reflector telescope25Newton’s telescopeAdvantage: no chromatic aberrationDemo26Telescope drives• Telescopes must rotate once every 24 hrs (approximately) to follow the stars, or the pictures will have streaks. NorthstarStudent telescopes27View of galaxyNGC130028Catadioptric telescopeAlso called Schmidt-CassegrainFront glass lens corrects aberrationsWhy buy this? It’s shorter.29Hubble Space Telescope imageCompare to studenttelescope image.30Palomar reflector - 5 meter mirror31South Africa Large Telescope (10 m)This shows 7 of the 91 mirrors. Diameter is about 10 m.Each mirror is a hexagon so that they pack closely. Former CU student Amanda Gulbisuses this telescope. 32Largest single mirrors are 8 m now33Finished mirror(don’t sneeze)34KeckTelescope36 mirrors10 m dia.35Magellan Telescope (yr. 2018)24.5 m dia. segmented mirror36European Extremely Large Telescope (42 m dia.) would use many smaller mirrorsDon’t twinkle, little star!Adaptive optics corrects for atmospheric turbulence, requires computer control. “Adaptive optics” is an additional mirrorthat can be deformed to correct the wave fronts that are “blurred” by atmospheric turbulence. Recall that you can “see” heat rising from a hot surface due to changes in the index of refraction with temperature. 38BinocularsSimply folded telescopes for each eye.39What does 7 x 50 binoculars mean? • 7x is the magnification• 50 is the diameter of the front lens (the objective lens) in millimeters • 6 x 30 binoculars are easy to carry• 7 x 50 binoculars are heavy, butthese give a brighter image• 15 x 80 binoculars need a