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

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

Class-designed problem 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

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

Aberrations

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

Clicker question: Chromatic Aberration 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 Lens-makers’ eqn:

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

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.

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

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? q

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.

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

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

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)