Exposure in photography generally refers to how much light is admitted through the lens, reaches the film, and for how long. This process is controlled by the APERTURE and the SHUTTER SPEED. The various combinations of lens aperture and shutter speed might add up to the same total exposure.
Aperture / "f stop": The lens diaphragms are calibrated in terms of different opening ratios which are calibrated so that each successive step (starting from the widest aperture) allows half the amount of light to the film. "2" is a HUGE aperture, for example, which lets in a lot of light, whereas 32 is a tiny aperture (letting in less light).
Shutter: The shutter is mainly a metallic curtain that covers the film from light. At the moment of exposure it opens at a chosen speed to let light through. The darker the scene, the longer the film needs to be exposed to light. The shutter speeds are calibrated in fractions of a second, and the numbers run from slow to fast (ie: 1" to 2000 — super slow—1 second, to be exact—to super fast).
Starting at the fast end (2000), each successive step permits double the amount of light. Note: 60 (1/60) is faster than 4 (1/4).
When shutter speeds below 60 are used, the hand movement will be captured on film, and the image will be blurry. In such a situation, the camera must be attached to a tripod.
Film Speed / ISO (International Standard Organization): The film speed means sensitivity or the quickness of its response to light. Greater speed ("fast film") permits good pictures to be made with little light; with less speed, more light is necessary. A "fast" film is made of larger grains of silver bromide, which result in high graininess. (Slow: 100 / Fast: 3200).
Light Meter: Based on the film speed used, the light meter indicates which aperture to use with the chosen shutter speed, or vice versa.
Meter at work:
Lenses:
Photography Fields:
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