Sensor Format and Equivalent Focal Length: Explaining the Angle of View Difference with Nikon FX / DX

FX and DX Are Nikon's Format Names

Nikon describes FX as approximately 36×24 mm, close to the 35 mm film format; DX sensors are smaller. DX captures a smaller portion of the image projected by the lens, so at the same shooting position and with the same lens, the field of view is narrower than FX. The dimensions and names here correspond to Nikon's FX / DX product system.〔G-SS-01〕

Equivalent Focal Length Compares the Field of View

Nikon summarizes the difference between DX and FX / 35 mm field of view as about a 1.5× crop factor. For example, Nikon explains that the angle of view of a 24 mm lens on a DX body is roughly equivalent to using a 36 mm lens on an FX / 35 mm format. The physical focal length of the lens does not change; "equivalent focal length" is used to compare the field of view. Crop factors vary between manufacturers and sensor formats, so calculations should use data specific to that camera.〔G-SS-02, G-SS-03〕

Format Differences Do Not Directly Determine Depth of Field

The crop factor indicates the recorded image area versus the field of view, not a change in lens focal length. Do not infer background blur or depth of field effects solely from the "equivalent focal length"; depth of field also depends on aperture, focus distance, composition, and output conditions. The original "equivalent aperture" fixed conversion table has been removed from this version to avoid reducing different shooting conditions to a single formula.

Lens Compatibility Should Be Checked by Camera and Lens Series

The image circle of Nikon DX and FX lenses and the camera body crop behavior depend on specific product combinations. Nikon states that some FX camera bodies automatically enter DX crop mode when a DX lens is mounted. Before purchasing or using, check the official compatibility information for that camera and lens; do not extrapolate the behavior of Nikon bodies to other mount systems.