Field of view and crop factor

Compare photographic lenses using either a diagonal crop factor and sensor aspect ratio, or the sensor’s actual width and height in millimetres. The reference frame is 36× 24 mm. A crop factor describes the ratio of diagonals, not automatically the ratio of widths.

For a sensor dimension s and focal length f, angle of view=2atan(s/(2f)). The diagonal 35 mm-equivalent focal length is f×crop. With the same 3:2 aspect ratio, width=36/crop; other aspect ratios change horizontal and vertical angles. Equivalent focal length matches diagonal view, not all axes when aspect ratios differ. Sensor dimensions are exact inputs, not camera presets.

The cone depicts the actual horizontal angle; it has no distance scale. A larger crop factor does not change the physical focal length. Ideal rectilinear lens focused at infinity: no fisheye projection, distortion, focus breathing or macro magnification. The chosen aspect ratio means a sensor/image area with that diagonal, not an automatic crop of a fixed camera sensor. Valid settings are retained.