VARIABLE FOCAL LENGTH LENS SYSTEM AND IMAGE PICKUP UNIT

A variable focal length lens system includes: first to fourth lens groups alternately having negative and positive refractive power; and an aperture stop; the first to fourth lens groups being arranged to allow a space between the first and second lens groups to be decreased and spaces between the second and third lens groups and between the third and fourth lens groups to be varied, thereby transition of the lens system from wide end state to telephoto end state being accomplished, the third lens group travelling to allow image-plane position variation caused by subject position variation to be compensated and satisfying a following conditional expression, 0.05