# Announcements 11/7/11

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Announcements 11/7/11  Prayer  Term project progress reports due Saturday night  Slinkies! (Joshua M, Thomas, Mike, Rachael, and Ken—this means you!)…
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Announcements 11/7/11  Prayer  Term project progress reports due Saturday night  Slinkies! (Joshua M, Thomas, Mike, Rachael, and Ken—this means you!) Frank & Ernest Class-designed problem  p = _____  Lens 1: f = _____  Distance to Lens 2 = _____  Lens 2: f = _____  q2 = ? Real or virtual?  Mtot = ? Upright or inverted?  Ray diagram? (for first lens, anyway) Quick writing  Draw the ray diagram for this situation: Converging lens, f = 20 cm, p = 80 cm Quick writing  Draw the ray diagram for this other situation: Converging lens, f = 20 cm, p = 15 cm Quick writing  Draw the ray diagram for this third situation: Diverging lens, f = -20 cm, p = 15 cm Reading Quiz  What’s the term used to refer to rays failing to focus because a lens is shaped incorrectly? a. elliptical aberration b. hyperbolic aberration c. parabolic aberration d. spherical aberration Spherical Aberration Credit: the next several slides were produced by Dr. Durfee Reducing Spherical Aberration with Aperture Spherical Aberration Reducing Spherical Aberration by Reversing Lens Coma 0 Degree Tilt 10 Degree Tilt 20 Degree Tilt 30 Degree Tilt 40 Degree Tilt 40 Degree Tilt + Aperture Thought question Chromatic Aberration  Red light coming from O produces an image at I. Where will blue light coming from O form an image? a. same place Lens-makers’ eqn: b. closer to the lens 1  1 1    n  1    c. farther from lens f  R1 R2  How does a camera work?  Simplest picture  What if you leave out the lens?  What’s a pinhole camera? Reading Quiz  What is the f-number of a lens? a. The focal length in meters b. The focal length in inches c. One over the focal length in meters d. The focal length divided by the diameter of the lens e. The focal length divided by 25 cm Thought question  How does the f-number of a lens relate to the half-angle of the “light cone” formed by parallel light entering the q lens? a. q  2cos1   1   f-number  b. q  sin 1  f-number   1  c. q  sin 1    f-number  d. q  tan 1  f-number  1  1  e. q  tan    2  f-number  Cameras: f-stops  Which has the higher f-number?  What’s the advantage of one over the other? Thought question  If you have trouble seeing things far away but can see close objects well, you are “near- sighted”. What kind of lenses do you need in your glasses? a. Converging lenses b. Diverging lenses Near point vs. Far point  Far point: how far away can you focus on things a. Regular person: fp = infinity b. Nearsighted person: fp = much smaller – For me, my fp  1 m (right eye), 0.5 m (left eye)  Near point: how close can you see things comfortably a. Regular person: np  25 cm b. Farsighted person: np = much larger How to fix things with glasses? Nearsighted: object at  cm  image at –fp (diverging lens) Farsighted: object at 25 cm  image at –np (converging lens)
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