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Physics Class Announcements and Term Project Progress Reports

This announcement provides information about prayer, term project progress reports, extra time on slinkies, and class-designed problem on lenses.

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Physics Class Announcements and Term Project Progress Reports

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  1. Announcements 11/5/12 • Prayer • Term project progress reports due Saturday night • Slinkies: Ryan & Clement Frank & Ernest

  2. From warmup Extra time on? (nothing in particular) Other comments? (nothing in particular)

  3. Class-designed problem • p = _____ • Lens 1: f = _____ • Distance to Lens 2 = _____ • Lens 2: f = _____ • Ray diagram? (for first lens) • Final q = ? Real or virtual? • Mtot = ? Upright or inverted? 5 mins for class to solve

  4. Quick writing • Draw the ray diagram for this situation: Converging lens, f = 20 cm, p = 80 cm

  5. Quick writing • Draw the ray diagram for this other situation: Converging lens, f = 20 cm, p = 15 cm

  6. Quick writing • Draw the ray diagram for this third situation: Diverging lens, f = -20 cm, p = 15 cm

  7. Aberrations

  8. Spherical Aberration Credit: the next several slides were produced by Dr. Durfee

  9. Reducing Spherical Aberration with Aperture

  10. Spherical Aberration

  11. Reducing Spherical Aberration by Reversing Lens

  12. Coma

  13. 0 Degree Tilt

  14. 10 Degree Tilt

  15. 20 Degree Tilt

  16. 30 Degree Tilt

  17. 40 Degree Tilt

  18. 40 Degree Tilt + Aperture

  19. Lens-makers’ eqn: Clicker question: • Red light coming from O produces an image at I. Where will blue light coming from O form an image? • same place • closer to the lens • farther from lens ChromaticAberration

  20. How does a camera work? • Simplest picture • What if you leave out the lens? • What’s a pinhole camera?

  21. From warmup If the camera is initially focused on a distant object, to focus on a close object , must the lens be moved away from the CCD or moved toward the CCD? Away from the CCD, because since the focal length of the lens is constant, if p gets smaller, q must get bigger.

  22. F-number • f# = The focal length divided by the diameter of the lens

  23. q Clicker question: • How does the f-number of a lens relate to the half-angle of the “light cone” formed by parallel light entering the lens?

  24. From warmup Suppose you are comparing two cameras which both use the same size sensor and the same zoom level. One of them gives the aperture specification as "f/2.8" whereas the other one is "f/2.2". Which one allows more light to reach the sensor? (Or do they allow the same?) f/2.2, because it increases the area of aperture That depends on how long the shutter is open for each one. The one with f/2.2 will let more light through in a given time, but if the shutter speeds are timed differently, then in a single picture they may let the same amount of light through, or either one may have more.

  25. Cameras: f-stops • Which has the higher f-number? • What’s the advantage of one over the other?

  26. Clicker 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? • Converging lenses • Diverging lenses

  27. Near point vs. Far point • Far point: how far away can you focus on things • Regular person: fp = infinity • 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 • Regular person: np  25 cm • 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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