Cameras that produce negatives smaller than 35mm are considered small-format cameras. Small-format cameras are preferable when you need maximum freedom of movement and a large number of negatives without reloading the camera. The accessories, lenses, and flash equipment can be carried easily, and commonly 36 frames may be taken rapidly without reloading the film. This type of camera is helpful for news and action photography where several pictures must be taken in a short time from various ranges and under varying light conditions. The primary disadvantage of small-format cameras is they produce small negatives. The smaller the negative, the more it must be enlarged in printing.

The most popular professional small-format camera is the 35mm single-lens reflex (SLR). This camera has a mirror in the path of the image formed by the lens that is reflected to a viewing screen for focusing and composition. This allows you to see what the lens sees regardless of the lens focal length or the lens-to-subject distance. The reflex system is simple and reliable. It has three main elements: a hinged mirror, a matte focusing screen, and a five-sided glass prism called a pentaprism The mirror, in the viewing position, is below the viewing screen and behind the lens. It is at a 45-degree angle and projects the image formed by the lens up to the focusing or viewing screen. The pentaprism reflects the image from the focusing screen, so you can see it in the camera eyepiece. Figure 4-4 shows the design of a typical SLR camera.

When the shutter release is pressed, the mirror swings up and out of the light path, so the light can reach the film. It also seals off the viewfinder, so light entering the eyepiece cannot reach the film. After the film is exposed, the mirror swings back down, and the image is visible again in the viewfinder.

CAUTION

The reflex mirror is thin glass coated on the front with silver, so care must be taken not to damage it by touching or scratching it. Follow only the procedures listed in the Planned Maintenance System (PMS) for cleaning camera mirrors.

Almost all 35mm cameras have focal-plane shutters. Focal-plane shutters simplify the construction of the camera and make interchangeable lenses smaller,

Figure 4-5. The shutter, aperture, and mirror operate in a precke 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