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Vision

Vision. Flexible, Converging lens, Whose focal length can be changed by pulling on it!. Eye anatomy. Retina. http://www.1800contacts.com/staticcontent/vision101/frames.html. common visual problems (or don’t show).

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Vision

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  1. Vision

  2. Flexible, Converging lens, Whose focal length can be changed by pulling on it! Eye anatomy Retina • http://www.1800contacts.com/staticcontent/vision101/frames.html common visual problems (or don’t show)

  3. “Accommodation”: the lens in our eyes can change shape (variable focal length) to enable us to focus on both near and far objects • Ciliary muscles strained • = shorter f • (To focus on close objects) • Ciliary muscles relaxed • = longer f • (To focus on far objects)

  4. Normal “20-20” Vision (see your handout!) Ideally  Ideally 10-15 cm Range of Clear Vision Far Point Near Point

  5. FARSIGHTED Can only see FAR objects CLEARLY (write this!!!) Rays from near objects don’t converge enough (eyeball is too short… hyperopia) Thus: use converging lens to correct for farsightedness

  6. Image, at or beyond their near point For a Farsighted Person… Object Near Point Far Point

  7. Far-sighted eye: lens too weak… eye too short

  8. NEARSIGHTED Can only see NEAR objects CLEARLY (write this!!!) Rays from far objects converge too much (eyeball is too long…myopia) Thus: use diverging lens to correct for nearsightedness

  9. For a Nearsighted Person… Object Near Point Image, at or before their far point Far Point

  10. Near-sighted eye: lens too strong… eye too long

  11. The unit “Diopters” (D) • Eye doctors refer to the refractive Power of a lens in Diopters, not focal length P=1/f A lens of P=4 diopters means f=1/4 m (greater converging power than a lens of P=3 diopters)

  12. Chromatic Aberration • blue refracts more than the red, • blue has a shorter focus.(demo this with lens as magnifying glass and light from OHP… lens close to OHP, move side to side to see rainbow)

  13. Correcting Chromatic Aberration • use a diverging lens with different n alongside the converging lens • Achromatic doublet (achormat) is often used to compensate for the chromatic aberration • the focuses for red and blue is then the same!

  14. Spherical Aberration • Spherical aberration comes from the spherical surface of a lens • The further away the rays from the lens center, the bigger the error is. • The image is improved if we cut out (stop) the rays from top and bottom

  15. Color Blindness (1 in 12 males are color blind! 1 in 100 females!) 29 45 56 6 8

  16. The colors affected are usually limited to green and red, which often appear as shades of tan or brown. Less often, the color blue may also be affected • WHAT CAUSES IT? • A genetic defect in your cones

  17. Rods and Cones • Cones (red, green, blue): for more precise vision, need strong light (AKA photopic vision). help to see colors (thus we don’t see color in dim light). Mostly distributed in the center of the retina (fovea). • Rods: for peripheral and night vision (AKA scotopic vision). Sensitive to light. Mostly distributed on sides of retina.

  18. Color Mixing of light • Primary colors: red, green, blue • When mixed together: • WHITE! • See http://pdukes.phys.utb.edu/PhysApplets/Colors/TabbedcolorBox.html

  19. Eye Fun Facts • Most people blink every 2-10 seconds.Each time you blink, you shut your eyes for 0.3 seconds, which means your eyes are closed at least 30 minutes a day just from blinking. • The reason cat's and dog's eyes glow at night is because of silver mirrors in the back of their eyes called the tapetum. This makes it easier for them to see at night. • An ostrich has eyes that are two inches across. Each eye weighs more than their brain. • A chameleon's eyes can look in opposite directions at the same time. • A newborn baby sees the world upside down because it takes some time for the baby's brain to learn to turn the picture right-side up.

  20. A person who sees more clearly under water than in air without eyeglasses is… 1) Nearsighted 2) farsighted 3) neither

  21. Nearsighted! The speed of light in water is less than in air, so the change in speed is less as light goes from water to your eye. Less refraction occurs. This makes all people more farsighted under water, which is advantageous if you’re nearsighted. If you’re very nearsighted, the image may fall on your retina and you’ll see as clearly under water as a person with normal vision who wears an air-enclosed mask.

  22. FunOptical Illusions

  23. What do you see?

  24. What do you see?

  25. Square A and B are the same shade of grey

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