Transcript The Eye
The Eye
Eye Dissected
The eye is an optical lens
system.
• Two single lenses
The goal of the eye is to focus
an image on the retina.
Corneal Lens
The cornea is a curved
membrane with fluid behind
it.
• Two indices of refraction
• ncorn = 1.376
• naq = 1.336
This is roughly the refraction
from air to water.
• Eye works poorly
underwater
R
(neye ns )
f
Crystalline Lens
The lens is a denser material
for fine focusing.
• nlens = 1.406 at maximum
Relaxed muscle provides little
additional focus.
• For distant objects
Contracted muscles provide
more focus.
• Relaxes tension and creates a
bulge
• For near objects
Accommodation
The focusing by the lens is
The moon subtends an angle
called accommodation.
of about 0.009 rad as seen
from the earth.
The size of the moon on the
retina comes from the image
triangle.
The relaxed lens forms a
combination with the cornea.
• Object focus 15.6 mm in front
of cornea
• Image focus 24.3 behind
• Optical center 17.1 mm in
front of the retina
Typical shifts in
accommodation are a few mm.
yi si
(17.1 mm)( 0.009 rad) 0.2 mm
Retina
The retina is the screen for the
eye.
• Light sensitive cells
• Neurons for signal
transmission
Ideally it should be at the focal
plane.
• Otherwise image is blurred
Pinhole Camera
A pinhole opening can act as a
single lens.
• Forces ray convergence at the
opening point
• Iris in eye can act as pinhole
lens
A pinhole camera is a box with
a pinhole opening to focus
light.
Single Lens Reflex
A single lens reflex (SLR)
camera acts much like an eye.
• Shutter like iris
• Lens fixed
• Adjust distance to screen
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