Patent ID: 8098441
Filing Date: 2012-01-17
Classification: G02B

Abstract:
1. An objective lens for endoscopes having a front lens unit and a rear lens unit with an aperture stop between the front lens unit and the rear lens unit, the front lens unit comprising, in order from an object side: the rear lens unit comprising: wherein the fourth lens element and the fifth lens element are cemented and the objective lens satisfies the following conditions: where SF is a shape factor of the first lens element and is a value expressed by SF=(R 2 +R 1 )/(R 2 −R 1 ) when a radius of curvature of an object-side surface of the first lens element is denoted by R 1 and a radius of curvature of an image-side surface of the first lens element is denoted by R 2 ; D is an equivalent air length along an optical axis from a vertex of the image-side surface of the first lens element to the aperture stop; f is a combined focal length of an entire system; θ is a half angle of view; D 1 is an actually measured distance along the optical axis from a vertex of the object-side surface of the first lens element to the aperture stop; D 2 is an equivalent air length along the optical axis from the aperture stop to a vertex of the image-side surface of the third lens element; f 1 is a focal length of the first lens element; and f 3 is a focal length of the third lens element.