Patent ID: 8542444

Claim:
An image pickup optical system for use in a capsule endoscope, which is accommodated in a capsule to be swallowed into a body and used to capture an image inside a body cavity through a dome-shaped powerless transparent cover constituting part of said capsule, said image pickup optical system satisfying a condition expressed by: −5.0≦Δ Zr/ΔZp≦ 5.0 when said image pickup optical system is disposed in front of an object in the shape of concave curved surface and image capturing is performed, wherein said ΔZr denotes a difference between a position of a real image surface with respect to light flux of a maximum angle of view 2ωmax and a position of said real image surface with respect to light flux of a half angle of view ωmax, and A ΔZp denotes a difference between a paraxial image forming position of a virtual object plane surface passing through an intersection point of said object and principal rays of 2ωmax and being vertical to an optical axis and a paraxial image forming position of a virtual object plane surface passing through an intersection point of said object and principal rays of ωmax and being vertical to said optical axis.