LENS
The photographic camera is a product of conver-
gent evolution, a process where similar forces give
rise to analogous though unrelated structures. What
is striking about the camera is the way it resembles
the eye. Some inventions intentionally mimic nat-
ure. In the case of the camera, the mechanism func-
tions like a biological structure, but for several
centuries it was developed without a working
knowledge of the physiology of vision.
Cameras contain two essential components: a
light-tight chamber and an aperture. In a properly
constructed camera, the aperture projects the scene
in front of it as a visible image within the chamber.
Modern cameras use light-sensitive substances to
capture, process, and transmit that image. Our vi-
sual apparatus functions in a similar manner, as
retinas process visual information projected by the
pinhole aperture seen within the iris.
Cameras can operate without a lens. These devices
are called pinhole cameras because the aperture
must be narrow enough to allow only one coherent
image into the chamber. Pinholes function by allow-
ing only one ray of light from each point of a visible
surface to reach the back of the camera chamber.
Pinhole cameras have the advantage of simpli-
city and infinite depth of field—every point within
the image is in focus—but the size of the aperture
sorely limits the intensity of the image. Conse-
quently photosensitive materials require several
minutes of exposure. In evolutionary terms, pin-
hole cameras correspond to the most primitive
eyes in nature, for instance those of a nautilus,
which also consist of a pinhole and simple retina.
The lens improves the efficiency of cameras by
gathering more light. Unlike a pinhole, which
approaches the spatial limit of zero, lens apertures
canbeoffinitesize,creatingabrightimagewithinthe
apparatus that reduces exposure time. The lens
retains the qualities of a pinhole by focusing light
from many different directions into a single coherent
image. A correspondingly large aperture—in other
words,ahole—projectslightincoherently,forminga
circular beam of illumination, not a visible image.
The lens functions through refraction, or the fact
that light bends when it passes through media of
different densities. Both the eye and the camera
exploit the structural capacity of a lens, one crys-
talline and the other organic, to focus light and
form a coherent, transmittable image within a dar-
kened chamber.
Though some ancient cultures may have discov-
eredsomeofthepropertiesoflenses,suchinquiries,if
theyhappened,lieoutsidethestreamofdevelopment
that led to the camera. The first reports of lenses in
our historic continuum appear in thirteenth century
Europe, where lenses were used to correct impaired
vision. A Venetian law book from 1300 refers toroidi
da ogli, ‘‘little disks for the eyes,’’ and in1306 sermon
Friar Giordana of Pisa reported that the art of mak-
ing eyeglasses was scarcely 20 years old.
In the sixteenth century, the lens became married
to the camera in its current use of amplifying the
intensity of projected images. It was first men-
tioned in mid-century by the Milanese polymath
Girolamo Cardano, who described how the visual
effects of the pinhole camera can be enhanced by
the insertion of a biconvex lens in the aperture:
If you want to see the things which go on in the street, at
a time when the sun shines brightly, place in the win-
dow shutter a biconvex lens. If you then close the win-
dow you will see images projected through the aperture
on the opposite wall....ii
Daniele Barbaro subsequently explained how to
focus by altering focal length and depth of field in
La Practica della perspettiva.iiiBut Giambattiste
della Porta was the first person to widely promote
the lens. InMagia Naturalishe recommends using
a biconvex lens to improve images within thecam-
era obscura, and his widely circulated text popular-
ized the camera as a tool for painters.
Lensmaking steadily improved after the Renais-
sance. Optical standards were established during
the eighteenth century, and the invention of photo-
graphy in the nineteenth century created a mass
market for lenses. Virtually every camera incorpo-
rates a lens. While pinhole cameras are functional,
they are impractical for most uses. And, while the
biconvex lens used in early photographic cameras
sufficed to brighten images, compound lenses were
required for the many advances of photography
since the nineteenth century.
Lens manufacturing advanced considerably dur-
ing the twentieth century. The main innovations layLENS