Nikon D850 User Manual page 311

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Calculating Angle of View (Continued)
The DX (24×16) angle of view is about 1.5 times smaller than the
35 mm format angle of view, while the 1.2× (30×20) angle of view is
about 1.2 times smaller, the 5 : 4 (30×24) angle of view is about
1.1 times smaller, and the 1 : 1 (24×24) angle of view is about 1.3 times
smaller. To calculate the focal length of lenses in 35 mm format,
multiply the focal length of the lens by about 1.5 when DX (24×16) is
selected, by about 1.2 when 1.2× (30×20) is selected, by about 1.1
when 5 : 4 (30×24) is selected, or by about 1.3 when 1 : 1 (24×24) is
selected (for example, the effective focal length of a 50mm lens in
35 mm format would be approximately 75 mm when DX (24×16) is
selected, 60 mm when 1.2× (30×20) is selected, 55 mm when
5 : 4 (30×24) is selected, or 65 mm when 1 : 1 (24×24) is selected).
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