Patent ID: 7170691

Claim:
A zoom lens system that projects, onto a screen, projection light from an image generating device, comprising, in order from a screen side thereof: a first lens group with a negative refractive power; a second lens group with a positive refractive power; a third lens group with a positive refractive power; a fourth lens group with a negative refractive power; and a fifth lens group with a positive refractive power, wherein zooming is performed by moving the second, third and fourth lens groups, the fourth lens group is composed of a negative meniscus lens that is concave on an image side, a cemented lens made up of a negative lens that is concave on the screen side and a convex lens, and a positive lens, and the zoom lens system satisfies conditions below 1.15 <f 2 /fw <2.0 50 <Δvd 4<70 where fw is a combined focal length of the zoom lens system at a wide-angle end, f 2 is a combined focal length of the second lens group, and Δvd 4 is a difference in respective Abbe numbers vd of lenses composing the cemented lens in the fourth lens group.