Patent ID: 7180686

Claim:
An image pickup unit for endoscope consisting of an objective optical system and a solid-state image pickup device, and having a maximum field angle of 150° or larger, wherein said objective optical system is composed of spherical lens elements and plane parallel plates, and consists of a first lens unit which comprises a first meniscus lens element having a convex surface on the object side and having negative refractive power and has negative refractive power as a whole, a second lens unit which comprises at least a convex lens element and has positive refractive power as a whole and an aperture stop which is disposed between the first lens unit and the second lens unit, and satisfies the following conditions (1), (2) and (3): 0.7 <f/IH< 1 (1) −1.2 <f 1 /f<− 0.7 (2) 0.9 <D/|f 1|<1.8 (3) wherein a reference symbol f represents a focal length of the objective optical system, a reference symbol IH designates a maximum image height in a display area of the solid-state image pickup device, a reference symbol f 1 denotes a focal length of the first lens unit and a reference symbol D represents an equivalent air distance as measured along an optical axis from an image side surface of the first lens element in the first lens unit to the aperture stop.