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Focal Length |
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Focal length is the distance from the film to the optical centre of the lens
when the lens is focused on infinity. On most adjustable cameras it is
marked in millimetres on the lens mount. On 35mm-format cameras, lenses with
a focal length of 50mm are called normal or standard lenses. Lenses of 35mm
or less are called wide angle lenses and lenses of 85mm or more are called
telephoto lenses. Lenses which allow varying focal lengths without changing
focus are called zoom lenses. Some confusion has arisen since the advent of digital cameras and a conversion factor has to be used to make a comparison between film cameras and digital cameras. For example, the conversion factor is around 1.6 for Canon and 1.5 for Nikon. Hence lenses of 23mm, 32mm, and 55mm on digital cameras are approximately equivalent to 35mm, 50mm and 85mm on 35mm film cameras. Focal length also has an effect on the depth of field – the distance between the nearest and furthest sharp objects in a photograph. A wide-angle (or short) lens will provide a greater depth of field than a long lens. |
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20 mm | ||
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28 mm | ||
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35 mm | ||
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50 mm | ||
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70 mm | ||
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85 mm | ||
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105 mm | ||
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135 mm | ||
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200 mm | ||
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300 mm |