minds-on. the human eye the eye vs. the camera the eyethe camera opens and closes to adjust the...
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Minds-on
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The Human Eye
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The Eye vs. the CameraThe Eye The Camera
Opens and closes to adjust the amount of light that enters
The Iris The diaphragm
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The Eye vs. the CameraThe Eye The Camera
The opening where light enters
The pupil The Aperture
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Dilated pupil: when in dim light
Constricted pupil: when in bright light
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The Eye vs. the CameraThe Eye The Camera
Refract light to form a smaller, sharp image
The lens and cornea
The lens
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The Eye vs. the CameraThe Eye The Camera
Surface where the image is created
retina Film or digital sensor
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Photoreceptor cells on Retina- Rod cells: detect object in low light; we see shades of grey- Cone cells: detect colors
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The Cornea-lens combination concentrates light to form a smaller, inverted and real image on the retina.
How the Brain ‘Sees’
Any question at this point?
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Electrical impulses from the retina travel through the optical nerve to the brain, where
the image is flipped so we ‘see’ upright.
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Accommodation: Changes the focal length of the lens by changing the lens shape(using eye
muscles) so that both close and distant objects can be seen clearly.
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Focusing Problems
Hyperopia (Far-Sightedness)Disability: can’t focus near
objects.Cause: eyeball is too shallowImage forms: beyond retinaCorrect with: A converging lens
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The converging lens, causes the light rays to intersect sooner so that the image focuses on the retina instead of beyond the retina.
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A positive meniscus is a thinner converging lens used in glasses.
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Focusing ProblemsMyopia (Near-Sightedness)Disability: can’t focus
distant objects.Cause: eyeball is too
deepImage forms: in front of
retinaCorrect with: A diverging
lens
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The diverging lens, causes the light rays to intersect later so that the image focuses on the retina instead of in front of the retina.
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A negative meniscus is a thinner diverging lens used in glasses.
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Focusing ProblemPresbyopiaDisability: can’t focus near
objects (small print) due to poor accomodation.
Cause: aging lens is less elastic, eye muscles are weakerLens does not thicken enoughImage forms: beyond retinaCorrect with: A converging lens
for reading
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For Presbyopia:The converging lens, causes the diverging light
rays (from close objects) to intersect sooner so that the image focuses on the retina instead of beyond the retina.
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Other Focusing Problems
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Astigmatism
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Colour Blindness
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Cataracts
Cataract = a medical condition in which the lens of the eye becomes progressively opaque, resulting in blurred vision.
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Tunnel Vision
a condition in which you can see things that are straight ahead of you but not to the side (i.e. loss of peripheral vision)
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Eye blood vessels burst
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