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Zoom lenses are often described by the ratio of their longest to shortest focal lengths. For example, a zoom lens with focal lengths ranging from 100 mm to 400 mm may be described as a 4:1 or "4 |
Some digital cameras allow cropping and enlarging of a captured image, in order to emulate the effect of a longer focal length zoom lens (narrower angle of view). This is commonly known as digital zoom and results in a lower quality image than optical zoom, as no optical resolution is gained. Many digital cameras have both, an optical and a digital zoom, combining them by first using the optical, then the digital zoom, so does the Canon PowerShot A720 IS which provides 6x optical zoom, 4x digital zoom resulting in a 24x combined zoom as both are multiplied. The optical zoom in this case can be calculated by dividing 34.8/5.8 as it is written on the lens tube of the camera, resulting in the zoom factor 6. |