Perspective is a two-dimensional representation of a three-dimensional scene. In photography this can be achieved by viewing 3-D objects from an angle rather than head-on. A photograph is also given perspective if there are objects in the foreground, middle distance and background, giving the whole scene "depth".
A lens which can be adjusted to a wide range of focal lengths without a change in focus, thus an alternative for a number of individual lenses of various focal lengths. A difficult type of lens to design and manufacture, but very useful for the photographer who likes to travel light.