Patent ID: 7854700

Claim:
A capsule-type endoscope comprising: a capsule; an image pickup unit that includes an objective optical system having an optical axis and a field of view, and an image pickup element; an illumination light source having a light emitting surface; and a transparent cover that seals the objective optical system, the image pickup unit, and the illumination light source within the capsule; wherein the light emitting surface of the illumination light source, which is planar, is positioned in such a manner that it does not overlap any part of an image of the entrance pupil of the objective optical system, said image being defined when hypothetical light rays emitted from the center of the entrance pupil at the outer limits of the field of view of the objective optical system are projected onto a plane Qm by being reflected by the inner surface of the transparent cover, where the plane Qm is the plane containing the light emitting surface of the illumination light source; an inner surface of the transparent cover is spherical within the field of view of the objective optical system so as to have a center of curvature, the center of curvature is offset from the optical axis of the objective optical system, and the following condition is satisfied: 0.01 <L 1 /R tan θ<0.5 where L 1 is the distance between the center of curvature of the inner surface of the transparent cover and the optical axis of the objective optical system; R is the radius of curvature of the inner surface of the transparent cover; and θ is the half-field angle of the objective optical system.