11Lecture 14 Ch. 5 – The Eye Finish Ch. 4. The camera. Start Ch. 5. The eye. Read Chapter 5. There will be a homework on ch. 5 due Oct. 14. Pick up a “blind spot” handout. DCTo change your iClicker frequency, turn on your iClicker. Hold down on the power button until the power light blinks. Then hit DC. You should see a green light indicating that you have changed the frequency. October 7, 201022Equivalent exposure settingsThese combinations give the same lightf number shutter speed1.4 1/250 sports event, stop motion2 1/1252.8 1/6041/305.6 1/1581/811 1/4 more depth of field233Which is best for a bird in a tree?A. focal length 200 mmB. focal length 50 mm44Which gives more light?A. f-number 4B. f-number 22355Which gives more light?A. shutter speed 1/4 secB. shutter speed 1/16 sec66Which f-number gives half the light of f-4?A. f-2B. f-2.8C. f-4D. f-5.6E. f-8477Which pair gives the same amount of light?1/30 sec. and f number 4 anda) 1/120 sec. and f-1b) 1/120 sec. and f-2c) 1/120 sec. and f-48Ch. 5 The Eye599• Anatomy: The parts of the eye• How the eye “works”• Night vision• Response time• Eye problems and fixesOutline10Evolution of the eye10Wikipedia611Comparison of eye to camera The cameraLensDiaphragm (f-stop)Focusing knobFilmThe eyeLens and corneaIrisCiliary muscleRetina12713Eye parts that you seeLens changes shape to focusCiliary muscle Suspensory ligamentIris changes its opening to adjust lightthe pupilis the openingSclera the white outer wall14The hyaloid canal in the fetus has an artery, but this regresses during development.815Focusingmostly by the corneaassisted to varying degrees by eyelensciliary muscles puff up to relax the lens for close focusing16IrisWide open at night , f/2 or f/3more aberrationsless depth of fieldClosed down in daytime, f/8fewer aberrationsmore depth of fieldYou can check depth of field:Try it: Close one eye, hold up thumb, stuff behind thumb is out of focus.917Retinahas 108nerve endings to detect imagerods, for night visioncones, for color and detail, 7 millionoptic nerve = 106transmission linesfovea, region of best vision (cones)18Rods and cones• Rhodopsin, a photochemical, responds to lightIt is destroyed and reformed.Signal goes to a synapse, a gap between nerve cells• There are 3 kinds of cones for 3 colors red, green, blue1019Retina detailsChoroid, outside layer with blood supplyPhotoreceptors: rods and conesPlexiform layer, inside layer with nerves(nerves are on top of photoreceptors)Photopicvision, in bright light, cones are usedScotopic, in low light, rods are usedmore rods per nerve combines signals20Some words• Aqueous humor, front fluid• Vitreous humor, back fluid• Blind spot = optic nerve attachment place1121Demo: handout blind spot locator22More about the eye• Night vision, dark adaptation• Response time•Eye problems– hyperopia, – myopia, – presbyopia, – astigmatism1223Dark adaptation (night vision)• Time to adapt to dark: ~30 minutes• Night adaptation: shifts to rods• Rods: more sensitive to blue (rod are for “black and white” vision)• Cones: more sensitive to red (color vision)• Purkinje shift: you see blue better in the dark • Red lights at the observatory help preserve night vision.24Persistence of vision• Images remain on receptors for – 1/25 second in low light– 1/50 second in bright light• Movies do 24 frames per second in a darkened room.• TVs do 60 frames per second, looks ok in a lighted room.Demo: bird in cage illusion1325Aberrations of the eyelens• Spherical aberrationCornea is not spherical surface (aspherical)Iris cuts out rays through the edge of the lensIndex of refraction is not uniform, which helps• Curvature of fieldretina is curved to correct for this• Chromatic aberration:Bluest light is absorbed26Eye problems• Loss of accomodation: good eyes can focus from 10 inches to infinity• Cataracts = cloudy eyelens, a replacement plastic lens does not accommodate • Floaters = dead cells floating in vitreous humor (seen against a clear sky)1427Eye problems continued• Myopia, see close objects clearly, fixed by a negative (diverging) lens•Hyperopia, see things far, fixed by a positive (converging) lens• Presbyopia, stiff lens, no accommodationBifocal glasses have near and far focal
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