Original: In addition to giving a wider angle of view, the image produced by a wide-angle lens is more susceptible to perspective distortion than that produced by a normal lens, because they tend to be used much closer to the subject.
Simplified: That way, an 18mm lens mounted on a digital camera of this type gives an angle of view of the 28mm wide-angle lens, namely 75 degrees, for a multiplier of 1.5.