A stepwise variable zoom lens system for creating an image of a scene on an image sensor includes a first lens unit which has a positive refracting power, an aperture, a second lens unit which has a positive refracting power, and a third lens unit which has a negative refracting power. Each of the first, the second and the third lens units is constructed from a single block. The third lens unit is fixed. The first and the second lens units are selectively positioned in a first position and a second position, and the position is changed from one to the other by moving the first and the second lens units in opposite direction.