| US 7,365,920 B2 | ||
| Four-piece lens assembly | ||
| Sayuri Noda, Taichung (Taiwan) | ||
| Assigned to Largan Precision Co., Ltd., His-Tun Dist., Taichung (Taiwan) | ||
| Filed on Dec. 28, 2005, as Appl. No. 11/389,127. | ||
| Prior Publication US 2007/0146901 A1, Jun. 28, 2007 | ||
| Int. Cl. G02B 9/12 (2006.01); G02B 13/18 (2006.01) | ||
| U.S. Cl. 359—784 [359/716; 359/738] | 8 Claims |
| 1. An four-piece lens assembly, in order from the object side, consisting of: an aperture, a first lens, a second lens, a
third lens, a fourth lens, a flat parallel glass and an image plane; wherein
the first lens is a double convex positive lens;
the second lens is a double concave negative lens or a plano-concave lens, and an object side surface of the second lens contacts
an image side surface of the first lens;
the third lens is a convex-concave positive lens whose convex surface facing the image side and has at least an aspherical
refractive surface; and
the fourth lens is a convex-concave positive lens whose convex surface facing the object side and has at least an aspherical
refractive surface;
a total focal length of the lens assembly is f, and a radius of curvature of an image side surface of the fourth lens is R42, then they satisfy the relation of:
2.0<f/R42<3.7.
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