aberrations. You may hear photographers talking about
aberrations as if they were important. They may make
an interesting subject, but knowing all the details about
them does not help you to take better photographs.
Important matters that will improve your skill as a
photographer are knowing how to control the factors,
such as exposure, composition, lighting, and lab work.
Let the lens designers and manufacturers worry about
the lens aberrations. However, just so you know what
these lens aberrations are, a brief definition is provided
for each of them in the glossary; they are as follows:
Astigmatism
Chromatic aberration
Coma
Curvilinear distortion
Spherical aberration
Today's lenses can image more detail than present
film materials can record. Therefore, avoid discussing
lens resolution. If you want to discuss resolution, talk
film resolution.
PRINCIPLE OF A LENS
The purpose of a camera lens is to control the light
rays entering the camera. The simplest kind of lens is a
pinhole in a piece of thin metal or black paper. Of course,
only an extremely small part of the light reflected by a
subject passes through the pinhole and enters the
camera. When the pinhole is large, it allows more light
rays to enter but blurs the image. This blur is really an
overlapping of several images. Images produced by
large and small pinholes are the same size, but one is
blurred, while the other is sharp. A photographic lens is
a piece of polished and carefully shaped glass that
refracts light rays so an image of a desired scene is
formed on the rear wall of a camera. A lens transmits
more light than a pinhole. It increases the brightness and
improves the sharpness of an image. The basic principle
of a lens-any lens-is relatively simple.
First, consider an image formed with a single
pinhole. Next, consider another pinhole above the first.
This pinhole forms a second image. When these two
images could be made to coincide, the result would be
an image twice as bright as the original. Now, consider
a third pinhole on the side of the first, a fourth on the
other side, and a fifth below the first. All four pinholes
project separate images slightly removed from the first
or center one. When these four images are made to
coincide with the center one, the result is an image five
times as bright as the image made by the one center
pinhole. By using the principle of refraction, you can
make these four images coincide with the center one. By
placing a prism behind each pinhole, you are causing the
light that forms each of the four images to be refracted
and form a single image. In other words, the more
pinholes and prisms used, the brighter or more intense
the image. A lens
represents a series of prisms
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