Patent ID: 7927273

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 element, wherein the following condition is satisfied 0.1 ≦|p·NA 2 /(0.61·λ·β 0 )|≦0.8 where p is the pixel size of the image pickup element, NA is the numerical aperture, λ is the wavelength at the e-line (546.1 nm), and βo is the image scale factor of the objective optical system, wherein: the objective optical system includes, in order from the object side, a front unit having positive refractive power, an aperture stop and a rear unit having positive refractive power, and the following condition is satisfied 2≦ f 2/ f 1≦10 where f2 is the focal length of the rear unit, and f1 is the focal length of the front unit.