advance system. The film advance is designed to
pull the film across the film plane (where the image
will be formed). Once the photograph is made, the
film advances the distance of one frame, or indivi-
dual picture area. In many point-and-shoot cam-
eras, advancing the film is done automatically.
Once the shutter is closed, a motor winds the
film to the next frame to ready the camera for
the next exposure. In a manual SLR, advancing
the film is done with a film advance lever. Motor
drives can be added to SLRs to automatically
advance the film. Some SLRs come with an inte-
grated motor drive.
The body also houses the shutter. A shutter is a
device used to regulate the amount of time light is
permitted to strike the film. The shutter is one of
two controls used to regulate exposure. Shutters in
35-mm cameras are typically of the focal plane
variety, meaning they are located directly in front
of the film, or focal plane. These shutters are com-
posed of either a set of cloth slit curtains or metal
leaves. The shutter speed is created by the curtains
or leaves moving in sequence, exposing the film
from side to side or top to bottom. The speed is
dependent on how fast the traveling slit moves
across the film.
Shutter speeds can range from 1 second to as fast
as^1 = 400 of a second. A standard shutter speed range
is: 1 sec (slowest),^1 = 2 ,¼,^1 = 8 ,^1 = 15 ,^1 = 30 ,^1 = 60 ,^1 = 125 ,^1 = 250 ,^1 = 500 ,
(^1) = 1000 (fastest). Increments of these speeds are typi-
cally double the time, or half the time, depending
on the direction. For example, changing the shutter
speed from^1 = 60 to^1 = 30 doubles the amount of light
striking the film, where as changing from a^1 = 60 to
(^1) = 125 cuts the amount of exposure in half. One of
these increments is typically known as a stop.
In addition to determining the amount of time
light is allowed to strike the film, shutter speeds are
also responsible for capturing motion. A long shut-
ter speed will blur motion; a short shutter speed
will capture it sharply.
In order for the camera to evaluate the amount
of light the film needs to make an exposure, it needs
a light meter. Virtually all modern 35-mm cameras
have built-in light meters, and depending on the
camera, the light meter can either set the exposure
controls automatically, or give the photographer a
guideline of what the exposure needs to be, allow-
ing for various effects.
Lens
The purpose of the lens is to focus the image on
the film plane. Depending on the camera, this
focusing can take place manually, by rotating the
lens collar, or automatically, in the case of auto
focus lenses and cameras. Auto focus lenses work
via infrared or ultrasonic sensors that determine
subject distance and then set the lens accordingly.
The lens contains the second key element in ex-
posure control, the aperture. The aperture is an
iris-like device set inside the lens to control the
amount of light that reaches the shutter. The ap-
erture is controlled either automatically through the
in-camera light meter, or manually through a series
of increments. These increments are called f/stops.
A typical f/stop range is as follows: f/2.8 (widest
opening), f/4, f/5.6, f/8, f/11, f/16, f/22 (smallest
opening). F/stops control how much of an opening
there is inside the blades of the aperture. Each in-
crement is half or double the next or last, respec-
tively. For example, changing the aperture from f/
11 to f/16 will halve the amount of exposure, while
changing from f/11 to f/8 will double it.
Aperture also controls depth-of-field, or the
amount of focus in an image. The smaller the aper-
ture opening (higher number), the greater the
amount of depth of field there will be in an
image. For example, a small aperture would allow
a person in a field to be focused as well as the field
behind them. A wider aperture (smaller number)
would mean the person was sharp, but the field
would drop out of focus.
Lens types
Most camera lenses have fixed focal lengths,
typically measured in millimeters. A ‘‘normal’’
lens is considered to mimic the average field of
view of the human eye, or 50 degrees of view if
you are looking straight ahead. To mimic this field
of view, a ‘‘normal’’ lens must be equal to the
physical diagonal of the film format being used.
In the case of 35-mm, this measurement equals
approximately 50-mm.
Short focal length lenses are any lenses that are
shorter than normal focal length. A 28-mm lens
would be considered a short focal length lens for
35-mm format. The shorter the focal length of the
lens, the wider angle of view it provides. A 28-mm
offers a 75field of view when on a 35-mm camera.
For this reason, short focal length lenses are often
known as wide-angle lenses.
Long focal length lenses are any lenses that
typically have an angle of view of 35or less. In a
35-mm, these would be any lenses that are 80-mm
or more in focal length. Long focal length lenses
enlarge the subject as they narrow the field of view.
Within this category are telephoto lenses, which are
specially designed long-focal length lenses that
CAMERA: 35 MM