To provide a zoom lens system being a large aperture aspherical zoom lens system and having a small F number at the end of a short focal distance and a low manufacturing cost by composing the zoom lens of a first positive lens, a second negative lens. a third negative lens and a fourth positive lens in order from the object side and satisfying a specified condition.
This lens system is composed, in order from the object side, of a first positive lens group L1, a second negative lens group L2, a third negative lens group L3 and a fourth positive lens group L4. A cover glass CG of CCD (solid-state image pickup element) is provided in the rear. An aspherical surface is located on the position satisfying the conditional relation: HASP/HMAX <0.35. HMAX: the height of the highest paraxial light ray at the end of a long focal distance for all surfaces and HASP: the height of the paraxial light ray at the end of a long focal distance for the aspherical surface. Consequently, a large aperture aspherical zoom lens having a F number of 0.9-1.0 at the end of the short focal distance is obtained at a low cost.
ITO TAKAYUKI
ENOMOTO TAKASHI
