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The zoom lenses that are a standard feature of most cameras sold today offer greater flexibility than the fixed focal length lenses of the past, covering a range of focal lengths from wide-angle through to telephoto.

On a film camera, the usual standard zoom has a focal range of 28-90mm. On a digital SLR it is usually 18-55mm, which gives a comparable angle of view. You can use a 28-90mm film lens on a digital SLR, but the focal range is not ideal, because it does not provide proper wide-angle coverage on the smaller sensor.

Zoom ranges are sometimes quoted as a factor – for example, ‘3x’, ‘4x’ or ‘5x’. This figure indicates the change in magnification across the zoom range. A 28-gomm zoom offers a 3.2x zoom range, for example, while a 28-135mm is a 4.8x zoom.

Zoom lenses with a longer focal range are more desirable, but they are also more expensive and much heavier. A lighter, inexpensive lens may be more useful on a camera that is going to be carried around all day.