![]() ![]() History of technology: Printing and photography Selenium cells, still used in some cameras, also generate a current but are larger and less sensitive. In older cadmium sulfide cells the light falling on the cell changed the latter’s resistance to a current passing through it. The cell usually is a silicon or other photodiode generating a current that is then amplified. In most modern cameras the current or signal acts on a microprocessor or other circuit that directly sets the shutter speed or lens aperture. ![]() The current may energize a microammeter or circuit controlling LEDs to indicate exposure settings. ![]() A light-sensitive cell generates or controls an electric current according to the amount of light reaching the cell. Exposure-metering systemsĮxposure meters, or light meters, measure the light in a scene to establish optimum camera settings for correct exposures. Modern reflexes have a pentaprism arrangement that permits upright, right-reading, eye-level viewing by redirecting the image from the horizontal screen on top of the camera. The traditional reflex camera, held at waist level, showed a laterally reversed view. The optical finder gives a direct upright and right-reading view of the subject with the camera held at eye level. Camera viewfinders may have parallax-compensating devices. This parallax error is insignificant with distant subjects with near ones it is responsible for the familiar fault of a portrait shot of a head that appears partly cut off in the picture even though it was fully visible in the finder. The upper section of a twin-lens reflex camera is such a reflecting finder.Īs the viewfinder axis in a camera other than a single-lens reflex does not usually coincide with the lens axis, the finder’s and the lens’s views do not exactly match. An alternative form is the reflecting viewfinder in which the photographer looks down into a field lens on top of the camera. Bright-frame finders show a white frame reflected into the view to outline the field recorded on the film. Most present-day finders are built into the camera and are compact lens systems. The simplest viewfinder is a wire frame above the camera front, with a second frame near the back to aid the eye in correct centring. The sighting devices in cameras lacking screens are called viewfinders they show how much of the scene will appear on the film. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! ![]()
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