Camera is an instrument used for taking photographs and making motion pictures. It is one of the most important means of communication, documentation and expression.
All cameras use the same basic principles to form an image. Light reflects from the scene being photographed and strikes the lens of the camera. The light passes through the lens and forms an inverted (upside down) image on the film at the back. The image can be sharpened by adjusting the distance between the lens and the film. Most of it has a focusing mechanism by which photographer moves the lens a short distance to sharpen the image. Other will automatically adjust this distance by means of a focusing mechanism that is sensitive to light, infra rays or sound waves.
A device called a shutter opens to let the light enter the camera. The shutter may be behind the lens, between two lenses, or directly in front of the film. The speed of shutter opening and closing determines how long the film is exposed to light. By opening and closing rapidly, the shutter can “freeze” an image in motion. Many cameras have adjustable shutter speeds, ranging from 30 seconds to 1/2000 of a second but some have electronic shutters that adjust speeds automatically.
A device called a diaphragm fits in front of, behind or within the lens and controls the amount of light entering. The diaphragm can be expanded on a cloudy day to let in more light or contracted on a sunny day to let in less light. Most cameras have an electric eye mechanism that measures the intensity of the light and automatically adjusts the diaphragm.
Types of cameras
Fixed-focus cameras, the most basic one and have a nonadjustable lens. Most models have a single diaphragm setting and only one or two shutter speeds. Most fixed-focus cameras use 110-size or 126-size film. This can take satisfactory photographs in ordinary daylight but not in dim light, because its lens does not admit much light.
Point-and-shoot cameras have many automatic features that make them easy to use. Electronic devices inside will automatically adjust the focus, set the light exposure and the shutter speed, and advance rewind the film. A built-in electronic flash automatically supplies light when too little light reflects off the subject. It is equipped with high-quality lenses that produce a sharp image. Some of them have a zoom lens.
Single-lens reflex cameras appeal to skilled amateur photographers and to professional photographers. The photographer views the subject through the lens rather than through a separate viewing lens. A mirror between the lens and the film reflects the image onto a viewing screen. When the shutter release button is pressed to take picture, the mirror lifts out of the way to allow the light to expose the film. Thus, the photographer sees almost the exact image that is recorded on the film.
Twin-lens reflex cameras have a viewing lens directly above the picture-taking lens. The image in the viewfinder appears on a flat screen on top. The photographers usually hold it at the chest or waist and look down into the viewfinder. The image appears reversed from left to right.
View cameras are the largest and most adjustable type. Most of them have an accordion-like body, with a replaceable lens in front. They have a large viewing screen instead of a viewfinder. It must be mounted on a stand for efficient operation and it can provide artistic distortion of a subject more effectively than any other kind of camera.
Instant cameras use the film that provides a print without first being developed into a negative. It produces a print 15 seconds to 2 minutes after the photographer takes a picture. The time varies according to the camera and the type of the film. Some instant one can take flash pictures and focus automatically as the photographer lines up a subject in the viewfinder.
Digital cameras create pictures that can be viewed on a television screen. Most of the lens focuses light on a light-sensitive mechanism called a charge-coupled device (CCD). The CCD changes the light into electronic signals. The electronic pictures can be stored on small magnetic discs similar to those used in computers.
Motion-picture cameras take pictures that re-create the motion of a subject when they are viewed. Professional movie makers generally use large cameras that take 35 or 16 millimeter film. Today, many amateur movie makers use camcorders.
Stereo cameras have two identical picture-taking lenses with matched shutters. When it takes a picture, each lens photographs the same subject, but from a slightly different angle. When shown on the device called a stereoscope or seen through glasses that polarize light, the two images blend in one picture that seems to have depth. It is made for taking photographs or for making movies.
Special-purpose cameras have been designed for industrial, medical, military and scientific uses. They include aerial cameras used in space and underwater cameras.
