The size of a digital camera sensor is usually specified in inches. However, the specified value does not indicate the actual size of the active sensor area. The sensor size specifications date back to the formerly used tube systems: The curvature of the imaging surface of the camera tube caused distortions to the display, reducing the usable capture area of a 1” tube to a rectangle with a diagonal of 16 mm.

With the introduction of the semiconductor sensor technology, the dimensional specifications were taken over from tube systems. For this reason, a sensor whose active area diagonal measures 16 mm is specified as a 1-inch sensor. The following illustrations show the most common sensor sizes. The diameter in inch multiplied with 2/3 equals approximately the actual sensitiv area in millimeters.

Fig. 11: Some common sensor sizes (in inch)

Fig. 12: Comparison of common sensor sizes and examples for different fields of view

The size of each single sensor cell (pixel) depends on the size of the active sensor area and the resolution. In general, less pixels over the same sensor area (or a larger sensor area with the same resolution) will result in greater photosensitivity of the sensor.