Wide Angle. Telephoto and Zoom Lenses on Digital Cameras

There is great confusion about focal lengths of lenses on digital cameras. The numbers quotes in specs for digital cameras are difficult to relate to the 35mm film camera world because if you rely on the strict measurements of focal length, then you have to take into consideration the dimensions of the digital sensor which varies from camera to camera and is almost always different than the dimensions of a 35mm film camera. Frequently you will see two numbers: one the optical zoom factor -- say 3x or 10x -- and the 35mm equivalent focal length. But to really make sure you understand your lens, you need to understand the relevant parameters that need to be considered when trying to characterize the focal length of a (zoom) lens in the digital camera world:

1. Focal length
2. 35mm equivalent focal length
3. Minimum focus range
4. Macro focus range
5. Optical zoom

The easiest way for people to understand the focal lengths of digital cameras with their varying sensor sizes is to use what the focal length would be if the sensor was the same as on "35mm Cameras". Of course that term isn't really accurate. It really refers to "135 film" where the image dimensions (i.e., the "sensor") is 36mm x 24mm.