Focal Length and Lens Angle

Two important pieces of information are marked at the front of a zoom lens: its maximum and minimum focal lengths (in inches or millimeters), and its maximum aperture or f-stop.

Altering the focal length

If you change the lens’s focal length by altering the zoom lens setting, the subject will look correspondingly larger or smaller in the picture; and the impression of distance can alter. Double the focal length and your subject appears twice as large (apparently closer) – but only half the previous height and width of the scene is visible. At the same time, depth appears squashed.

If instead you halve the focal length, the subject is shown half the original size (apparently further away). The shot shows twice as much ...

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