Patent ID: 8098441

Claim:
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: a first lens element with negative refracting power of a meniscus shape, with a convex surface facing the object side; and a second lens element with positive refracting power, and the rear lens unit comprising: a third lens element with positive refracting power, with an absolute value of a radius of curvature of an image-side surface being lower than an absolute value of a radius of curvature of an object-side surface; a fourth lens element with positive refracting power; and a fifth lens element with negative refracting power, wherein the fourth lens element and the fifth lens element are cemented and the objective lens satisfies the following conditions: −2< SF<− 0.9 0.94< D /( f ×sin θ)<1.7 0.93<( D 1 +D 2 −f 1 )/(2× f 3 )<1.13 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.