The lens and its features
A lens is essentially one or more pieces of glass designed to manipulate
the rays of light that enter a camera. These glass elements are shaped
and combined in special ways to produce clear, sharp images on film.
However, as important as they are, the glass elements cannot do it
alone. To function properly, they must work in harmony with supportive
hardware such as the lens barrel.
The lens barrel is fundamental to the total lens system, for it holds
all the other components together. Without the barrel to keep the lens
elements precisely centered and at the correct distance from the sensor
and each other, these elements could not be used to create photographs.
The iris diaphragm (built into a lens about midway between the various
elements) is one such control device. Although the glass elements in a
lens actually form the image and determine its size and quality, the
diaphragm is needed to help regulate the light reaching the sensor.
No matter what equipment a lens contains, it must be controllable. Rings
around the outside of the lens barrel usually serve this purpose.
Focusing and diaphragm control rings are basic and common. However,
there may be other rings as well.
More about Camera