Forming and exposing an image
Forming and exposing an image | ||
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Most aspects of forming an optical image of your subject apply to both film and digital photography. Light from the subject of your picture passes through a glass lens, which bends it into a focused image. The lens is at the front of a light-tight box or camera with a light-sensitive surface such as film facing it at the other end. Light is prevented from reaching the film by a shutter until your chosen moment of exposure. The amount of exposure to light is most often controlled by a combination of the time the shutter is open and the diameter of the light beam passing through the lens. The latter is altered by an aperture, like the iris of the eye. Both these controls have a further influence on visual results. Shutter time alters the way movement records blurred or frozen; lens aperture alters the depth of subject that is shown in focus at one time (depth of field). You need a viewfinder, focusing screen or electronic viewing screen for aiming the camera and composing, and a light measuring device, usually built in, to meter the brightness of each subject. The meter takes into account the light sensitivity of the material on which you are recording the image and reads out or automatically sets an appropriate combination of lens aperture and shutter speed. With knowledge and skill you can override these settings to achieve chosen effects or compensate for conditions which will fool the meter. | ||