Nikon D7100 User Manual page 330

A
Calculating Angle of View
The size of the area exposed by a 35mm camera is 36 × 24 mm. The size of the area exposed
by the D7100 when DX (24×16) is selected for Image area in the shooting menu, in contrast,
is 23.5 × 15.6 mm, meaning that the angle of view of a 35mm camera is approximately 1.5
times that of the D7100 (when 1.3× (18×12) is selected, the size of the area exposed is
reduced and the angle of view is reduced by a further 1.3×).
Lens
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Picture size when DX (24×16) is selected
Picture size when 1.3× (18×12) is selected
Angle of view when DX (24×16) is selected for Image area
Angle of view when 1.3× (18×12) is selected for Image area
Picture size (35mm format)
(36 × 24 mm)
for Image area (23.5 × 15.6 mm)
for Image area (18.8 × 12.5 mm)
Picture diagonal
Angle of view (35mm format)