Patent ID: 7160249

Claim:
An image pickup unit for picking up magnified images of an object, comprising: an objective optical system having an image scale factor with an absolute value greater than unity and an image pickup surface, wherein the objective optical system includes, in order from the object side, a front lens unit having positive refractive power and an aperture stop having an opening, and the objective optical system satisfies the following conditions 0.9≦|cos wy ′/cos wy|≦ 1.1 0.2≦Φ1/(Φ2 ·f 1)≦2 where wy′ is the angle at which the chief ray corresponding to the largest half-field angle is incident onto the image pickup surface, wy is the half-field angle of a ray incident onto the image pickup surface, Φ 1 is the diameter of the opening of the aperture stop, Φ 2 is the largest outer diameter of the objective optical system, and f 1 is the focal length of the front lens unit.