Patent ID: 6994668
Filing Date: 2006-02-07
Classification: G02B

Abstract:
1. An endoscope objective lens formed of only four lens groups, in order along an optical axis from the object side, as follows: a first lens group having negative refractive power; a second lens group having positive refractive power; a diaphragm; a third lens group having positive refractive power; and a fourth lens group having positive refractive power; wherein said first lens group includes a first lens element having negative refractive power and the image side lens surface of said first lens element is concave; said second lens group includes a lens component that includes second and third lens elements; said third lens group includes a fourth lens element having positive refractive power and said fourth lens element has its lens surface of smaller radius of curvature on its image side; said fourth lens group includes a lens component that includes a fifth lens element having positive refractive power and a sixth lens element that is a meniscus lens element having negative refractive power; and the following conditions are satisfied: where d is the distance along the optical axis between the concave lens surface of said first lens element and said diaphragm; f f is the focal length of the endoscope objective lens; h is the maximum height of an image formed by the endoscope objective lens; f ν ν ν ν |R| is the absolute value of the radius of curvature of the adjoining lens surfaces of said fifth lens element and said sixth lens element; and Bf is the back focal length of the endoscope objective lens.