Patent ID: 11525998

Abstract:
The objective lens unit includes, a front lens group having a negative refractive power, a diaphragm, and a rear lens group having a positive refractive power, in order from an object side. The front lens group includes a negative lens having a concave surface facing an image surface side, and a positive lens having a convex surface facing the object side, and the rear lens group includes a positive lens having a convex surface facing the image surface side and a cemented lens in which a positive lens and a negative lens are cemented. The endoscope objective lens unit satisfies −1.6<fF/fR<−1.2 and −1.0<SF5<−0.5. fF and fR are the focal lengths of the front lens group and the rear lens group, SF5 is (R51+R52)/(R51−R52), and R51 and R52 are respectively the curvature radiuses of surfaces.