sequence when exposures are made.
lighter, and less expensive. The shutter, aperture, and
mirror work together in a precise sequence that is
repeated each time the shutter is tripped (fig. 4-5).
Most SLR lenses have an iris diaphragm. The
diaphragm is held wide open for focusing and viewing.
The aperture is then stopped down automatically to the
preset working aperture at the instant the exposure is
made. That means the image on the viewing screen is
bright, easy to see, and focus; but only controlled
brightness reaches the film for exposure.
Focusing is done by turning the lens focusing ring.
A screw thread that runs around the inside of the lens
barrel moves the lens closer or farther away from the
film as the focusing ring is turned. The interchangeable
lenses of most 35mm cameras are attached by a bayonet
flange. Each lens mount differs slightly for each
manufacturer of lenses and cameras, thus different
lenses and camera bodies cannot be interchanged.
Most 35mm SLRs have a built-in light meter that
reads through the lens (TTL). The light meter may read
the light falling on the mirror, the shutter curtain, the
focusing screen, or even on the film at the instant of
exposure. On an automatic camera, the f/stop or shutter
speed is adjusted automatically for correct exposures.
On manual cameras, the light meter produces a display
in the viewfinder to indicate the correct camera settings.
You must then set the camera controls to get the correct
exposures.
MEDIUM-FORMAT CAMERAS
Medium-format cameras are very popular in Navy
imaging facilities. Except for the increased size, these
cameras are just as versatile as small-format cameras.
Interchangeable lenses, TTL metering, SLR focusing
systems, and both manual and automatic controls are
available on medium-format cameras. The advantage of
a medium-format camera is the larger negative size of
120 or 220 film. These cameras are commonly used for
portraiture or when relatively large prints are required
from the negative. The most common medium-format
camera used by Navy imaging facilities is the Bronica
ETRS (fig. 4-6). This camera is available in almost all
Navy imaging facilities, both afloat and ashore.
LARGE-FORMAT CAMERAS
Large-format cameras are used when you must
retain maximum detail in the negative. This is necessary
when certain subjects are photographed to exact scale
or when large prints are required. Large-format cameras
produce negatives 4x5 or larger. The most common
large-format cameras are view cameras and copy
cameras. Features common to all large-format cameras
are as follows:
Ground glass viewing and focusing
4-4

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