Download - Announcements 11/7/11
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)