Footnote on Digital Compact Cameras
Digital compact cameras are fitted with lenses with short focal lengths to create 35mm equivalent field of views on their small sensor surfaces. Typically the sensor diagonal is 4 times smaller than the diameter of 35mm film. A 7mm lens fitted on such a camera will have the same field of view of a 7mm x 4 or 28mm lens on a 35mm film camera. Just like the digital lenses for digital SLRs, these lenses are designed to generate image circles to cover the smaller sensor. This allows these lenses to be much smaller and cheaper to manufacture. Because of the very small focal lengths used, the depth of field is much larger (2) than digital SLRs or 35mm film cameras with the same field of view.