Physics 1230: Light and Color Ivan I. Smalyukh, Instructor

Office: Gamow Tower, F-521 • Email: • ivan.smalyukh@colorado.edu • Phone: 303-492-7277 • Lectures: • Tuesdays & Thursdays, • 3:30 PM - 4:45 PM • Office hours: • Mondays & Fridays, • 3:30 PM – 4:30 PM • TA: Jhih-An Yang • jhihan.yang@colorado.edu Physics 1230: LightandColorIvan I. Smalyukh, Instructor Class # 12

Announcements • HW #3 Due today; • Exam #1 - October 11; • Overview of Exam #1 material today;

Thin convex lens: three easy rules for ray tracing } focal length • A ray parallel to the axis is deflected through the focus on the other side • A ray through the center of the lens continues undeviated • A ray coming from the focus on one side goes out parallel to the axis on the other 1 2 F’ F 3 3 foci Ray might have to be extended

Thin concave (diverging) lens: three easy ray rules • A ray parallel to the axis is deflected as if it came from the focus • A ray through the center of the lens continues undeviated • A ray aimed at the focus on the other side comes out parallel 1 2 F’ F 3 Ray might have to be extended For diverging lens focal length defined to be negative

Magnification formula S0 = object height Si = image height Note the similar triangles. Distances below the horizontal axis are defined as negative. Demo: big mama lens and bulb

Image distance equation F = focal length XO = object distance XI = image distance Usually, F is given. Distant objects: Let Xo be very large, say 1,000,000 meters. Then 1/Xo = 0.000001, which is very small. You can ignore it. Then For distant objects, the image is at the focal point (ask a burnt ant) Demo: find focal length of lenses

What is lens power (or diopters)? Lens power: D = 1/F Units of D are 1/meters, also called diopters Eyeglass lenses are measured in diopters. Example: D = 2/m = what focal length? F = 1/D = 1/(2/m) = (1/2) m = 0.5 m

How thin lenses add Ftot = final focal length F1= focal length lens 1 F2 = focal length lens 2 Diverging lenses (concave) have negative focal lengths This is the same as adding powers: Dtot = D1 + D2 Demo: put together some lenses

Compound Lenses • Can have less aberration. • A modern lens can have 16 elements and can “zoom”. “stop” Reduces aberration Image plane

Ch. 3 – Spherical mirrors and lenses Virtual images (review) Spherical mirrors Spherical lenses 3 formulas Aberrations of lenses We are here 10 10

Aberrations • Field curvature • Off-axis aberration • Spherical aberration • Distortion • Chromatic aberration

Aberration: field curvature Image does not lie in one plane

Off axis aberration Edges of images are less clear. Demo with lens and bulb

Spherical aberration Rays at the edge focus closer to the mirror Demo with lens, not mirror

Aberrations: Distortion Demo with overhead and small lenses

Chromatic Aberration Demo with lens and bulb

Web tutorials with Java Applets • Useful web links on curved mirrors • http://micro.magnet.fsu.edu/primer/java/mirrors/concavemirrors/index.html • http://micro.magnet.fsu.edu/primer/java/mirrors/convexmirrors/index.html • http://micro.magnet.fsu.edu/primer/java/mirrors/concave.html • Useful web links on lenses • http://micro.magnet.fsu.edu/primer/lightandcolor/lenseshome.html • http://micro.magnet.fsu.edu/primer/java/lenses/simplethinlens/index.html • http://micro.magnet.fsu.edu/primer/java/lenses/converginglenses/index.html • http://micro.magnet.fsu.edu/primer/java/lenses/diverginglenses/index.html • http://micro.magnet.fsu.edu/primer/java/components/perfectlens/index.html • http://micro.magnet.fsu.edu/primer/java/mirrors/convex.html 17

Fresnel Lens Used in lighthouses Lighthouse lens Fresnel stage light

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Physics 1230: Light and Color Ivan I. Smalyukh, Instructor