Patent attributes
An objective lens for endoscopes has a front lens unit and a rear lens unit with an aperture stop between them. The front lens unit includes a first lens element with negative refracting power and a second lens element with positive refracting power, and the rear lens unit includes a third lens element with positive refracting power, a cemented lens component of a fourth lens element with positive refracting power and a fifth lens element with negative refracting power. The objective lens satisfies the following conditions:−2<SF<−0.90.94<D/(f×sin θ)<1.70.86<(D1+D2−f1)/(2×f3)<1.13where SF is the shape factor of the first lens element; D is a distance from the vertex of the image-side surface of the first lens element to the aperture stop; f is the combined focal length of the entire system; θ is a half angle of view; D1 is an actually measured distance from the vertex of the object-side surface of the first lens element to the aperture stop; D2 is a distance from the aperture stop to a vertex of the image-side surface of the third lens element; f1 is the focal length of the first lens element; and f3 is the focal length of the third lens element.
