Nikon D800E User Manual page 402

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Calculating Angle of View
The D800 can be used with Nikon lenses for 35mm (135) format cameras.
If Auto DX crop is on (0 79) and a 35mm format lens is attached, the
angle of view will be the same as a frame of 35mm film (35.9 × 24.0 mm);
if a DX lens is attached, the angle of view will automatically be adjusted
to 23.4 × 15.6 mm (DX format).
To choose an angle of view different from that of the current lens, turn
Auto DX crop off and select from FX (36×24), 1.2× (30×20),
DX (24×16), and 5 : 4 (30×24). If a 35mm format lens is attached, the
angle of view could be reduced by 1.5 × by selecting DX (24×16) or by
1.2 × by selecting 1.2× (30×20), to expose a smaller area, or the aspect
ratio could be changed by selecting 5 : 4 (30×24).
Lens
n
378
FX (36×24) picture size (35.9 × 24.0 mm,
equivalent to 35mm format camera)
1.2× (30×20) picture size
(23.4 × 15.6 mm, equivalent to DX
Angle of view (FX (36×24);
Angle of view (1.2× (30×20))
Angle of view (DX (24×16); DX format)
Angle of view (5 : 4 (30×24))
(30.0 × 19.9 mm)
DX (24×16) picture size
format camera)
5 : 4 (30×24) picture size
(30.0 × 24.0 mm)
Picture diagonal
35mm format)