At the heart of every digital camera is a CCD or CMOS chip. This chip collects light from the lens and converts it into an image that the camera can use.

Chips vary in size and the area that collects light is usually smaller than the area that is exposed to light on a 35mm film camera.

The conversion factor is the ratio of CCD or CMOS chip size against 35mm film size. The resulting number is used to multiply the focal length of the lens in use and find out what the effective focal length equivalent would be.

For example:

Conversion factor = 1.25
Lens Focal Length = 28-80mm
Effective Focal Length = 35-100mm.