Nikon D300 User Manual page 382

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Calculating Picture Angle
The size of the area exposed by a 35mm camera is 36 × 24 mm. The size of
the area exposed by the D300, in contrast, is approximately
23.6 × 15.8 mm, meaning that the diagonal picture angle of a 35mm
camera is approximately 1.5 times that of the D300. To calculate the focal
length of lenses for the D300 in 35mm format, multiply the focal length of
the lens by 1.5 (for example, the effective focal length of a 24mm lens in
35mm format would be 36 mm when mounted on the D300).
Picture size (35mm format)
(36 × 24 mm)
Picture diagonal
Lens
Picture size (D300)
(23.6 × 15.8 mm)
Picture angle (35mm format)
Picture angle (D300)
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