Structure of the
Visual System
Basic Optics
Parts of the eye
Pinhole Camera
Camera Obscura
Diverging
•
•
•
•
Reflected light goes in all directions
From each point on object
Only very small part passes into camera obscura
At infinity rays are parallel
A Small Pupil
Kuppers, 1972, p.25
A Large Pupil
Kuppers, 1972, p.25
Functions of the Pupil
• Lens gather light
• Lens also create problems
– Spherical Aberration
– Limited depth of Field
• Iris/Pupil us used to change the trade-off.
– Bright -> smaller for better optics
– Dim -> optimize for more light gathering
.
Spherical Aberration
• Different parts of lens converge to different
focal points.
.
Spherical Aberration
• Reduced by small pupils: clearer vision
.
Depth of Field
The smaller the pupil, the larger the
range of depths over which objects
will be in focus.
Pinhole
Camera
• Objects at different distances will be in focus.
Infinite depth of field.
• Image plane of film is not critical for focus.
.
Large Lens
• Objects at different distances will be in
focus at different distances behind lens
• Narrow depth of field.
.
Depth of Field
• Only one distance is
in “perfect “ focus.
• But all sensors have
finite sizes
• Can not tell whether
in perfect focus and a
small circle of
confusion
• Therefore always a
range of distances in
measurable focus.
Lens
• Narrower cones of light.
• Smaller circles of confusion
• Larger depth of field.
.
Retinal Surface
Optic Disk