Patent ID: 6061187
Filing Date: 2000-05-09
Classification: G02B

Abstract:
A zoom lens system for imaging an object in an image plane, the lens system when viewed from the object side, comprising:a first lens group with a positive refractive power;a second lens group with a positive refractive power; anda third lens group with a negative refractive power;wherein when zooming from a wide-angle position to a telephoto position, the first, second and third lens groups move towards the object side while the distance between the first lens group and the second lens group increases and the distance between the second lens group and the third lens group decreases;the first lens group comprising a meniscus lens which has a negative refractive power and a concave surface facing the object side;wherein the zoom lens system satisfies the following conditions:ft/fw>4.10Lt/ft<0.901.60<(Lt-Lw)/fw<2.301.60<(fbt-fbw)/fw<2.300.6<.vertline.(R1-R2)/(R1+R2).vertline.>1.30whereinfw is the focal length of the zoom lens system at the wide-angle position;ft is the focal length of the zoom lens system at the telephoto position;Lw is the distance between the surface facing the object of the lens closest to the object of the first lens group and the focal plane at the wide-angle position;Lt is the distance between the surface facing the object of the lens closest to the object of the first lens group and the focal plane at the telephoto position;fbw is the back focal length at the wide-angle position;fbt is the back focal length at the telephoto position;R1 is the radius of curvature of the object side surface of the meniscus lens in the first lens group; andR2 is the radius of curvature of the image plane side surface of the meniscus lens in the first lens group.