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DX/FX

DX and FX are the designation that Nikon gives to APS-C format and full-frame cameras, respectively. A ‘crop’ mode is available in FX cameras, enabling you to shoot with DX format lenses using only the central region of the image sensor.

Focal length

This is measured in millimetres. In photographic lenses the angle of view is inversely proportional to the focal length.