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 aberrationb. hyperbolic aberrationc. parabolic aberrationd. spherical aberration

Spherical AberrationSpherical Aberration

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

Reducing Spherical Aberration with Reducing Spherical Aberration with ApertureAperture

Spherical AberrationSpherical Aberration

Reducing Spherical Aberration by Reducing Spherical Aberration by Reversing LensReversing Lens

ComaComa

0 Degree Tilt0 Degree Tilt

10 Degree Tilt10 Degree Tilt

20 Degree Tilt20 Degree Tilt

30 Degree Tilt30 Degree Tilt

40 Degree Tilt40 Degree Tilt

40 Degree Tilt + Aperture40 Degree Tilt + Aperture

Thought question

Red light coming from O produces an image at I. Where will blue light coming from O form an image?

a. same placeb. closer to the lensc. farther from lens

1 2

1 1 11n

f R R

Lens-makers’ eqn:

Chromatic Aberration

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 metersb. The focal length in inchesc. One over the focal length in metersd. The focal length divided by the

diameter of the lense. 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 lens?

a.

b.

c.

d.

e.

1 1tan

2 f-number

1tan f-number

1 12cos

f-number

1 1sin

f-number

1sin 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 lensesb. Diverging lenses

Near point vs. Far point

Far point: how far away can you focus on thingsa. Regular person: fp = infinityb. 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 cmb. Farsighted person: np = much largerHow to fix things with glasses?

Farsighted: object at 25 cm image at –np (converging lens)

Nearsighted: object at cm image at –fp (diverging lens)