Nikon D3X User Manual page 412

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Picture Angle and Focal Length
The D3X can be used with Nikon lenses for 35mm (135) format cameras. If
[Auto DX crop] is on (the default setting) and a 35mm format lens is
attached, the picture angle will be the same as a frame of 35mm film
(35.9 × 24.0 mm); if a DX lens is attached, the picture angle will
automatically be adjusted to 23.6 × 15.7 mm (DX format).
To choose a picture angle different from that of the current lens, turn
[Auto DX crop] off and select from [FX format (36 × 24)], [DX format
(24 × 16)], and [5 : 4 (30 × 24)]. If a 35mm format lens is attached, the
picture angle could be reduced by 1.5 × by selecting [DX format (24 × 16)],
exposing a smaller area, or the aspect ratio could be changed by selecting
[5 : 4 (30 × 24)].
[FX format (36 × 24)] picture size (35.9 × 24.0 mm,
equivalent to 35mm format camera)
Picture diagonal
Lens
[DX format (24 × 16)] picture size
(23.6 × 15.7 mm, equivalent to DX
format camera)
[5 : 4 (30 × 24)] picture size
(30.0 × 24.0 mm)
Picture angle ([FX format (36 × 24)];
35mm format)
Picture angle ([DX format (24 × 16)]; DX format)
Picture angle ([5 : 4 (30 × 24)])
The [DX format (24 × 16)] picture angle is about 1.5 times smaller than the
35mm format picture angle, while the [5 : 4 (30 × 24)] picture angle is
about 1.1 times smaller. To calculate the focal length of lenses in 35mm
format when [DX format (24 × 16)] is selected, multiply the focal length of
the lens by about 1.5, or by about 1.1 when [5 : 4 (30 × 24)] is selected (for
example, the effective focal length of a 50mm lens in 35mm format would
n
be 75 mm when [DX format (24 × 16)] is selected, or 55 mm when [5 : 4
(30 × 24)] is selected).
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