Nikon D750 DSLR Camera (Body Only) - Manual (Page 460)

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Calculating Angle of View
The D750 can be used with Nikon lenses for 35mm (135) format
cameras. If
Auto DX crop is on ( 0 111) 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 23.5 × 15.7 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 (36Ч24) , 1.2Ч (30Ч20) , and DX
(24×16) . 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 1.2Ч
(30Ч20) to expose a smaller area.
The DX (24×16) angle of view is about 1.5 times smaller than the
35mm format angle of view, while the 1.2Ч (30Ч20) angle of view is
about 1.2 times smaller. To calculate the focal length of lenses in
35mm format when
DX (24×16) is selected, multiply the focal length
of the lens by about 1.5 or by about 1.2 when 1.2Ч (30Ч20) is selected
(for example, the effective focal length of a 50mm lens in 35mm format
would be 75 mm when
DX (24×16) is selected or 60 mm when 1.2Ч
(30Ч20) is selected).
Lens
FX (36×24) picture size (35.9 × 24.0 mm,
equivalent to 35mm format)
Picture diagonal
DX (24×16) picture size (23.5 × 15.7 mm,
equivalent to DX format camera)
Angle of view ( FX (36×24) ; 35mm format)
Angle of view ( DX (24×16) ; DX format)
1.2Ч (30Ч20) picture size
(29.9 × 19.9 mm)
Angle of view ( 1.2Ч (30Ч20) )