Patent ID: 7554753

Claim:
A fisheye lens with an angle of incidence of at least 60 degrees, comprising a front group made up of a total of three groups, which are, in order from the object side, two concave lenses whose concave surfaces are directed toward the image side, and a compound lens whose concave surface is directed toward the image side and which has an overall convex or concave refractive power; and a rear group formed by three groups of convex lenses, wherein the front group includes at least one compound lens set, the rear group includes only one compound lens set, and at least a first surface of a first concave lens of the front group is an aspheric surface, and satisfies the following conditions: (1) The aspheric first surface of the first concave lens of the front group either is expressed by the formula X=G(Y), where the origin is the apex of the aspheric surface, X is the optical axis direction, and Y is a direction perpendicular to the optical axis (a positive value), or is expressed as a functional approximation by the formula dx/dY>0 within the range of Y max >Y>0.5f, where Y max is the maximum value of the effective radius of the lens, and f is the focal distance of the lens system overall, (2) When the projection function of the lens is taken using h=f*sin ω as a reference scale, the distortion aberration V when the incidence angle ω is 60 degrees is such that −10%≧V≧−16%. Here, V=(H−h)*100/h (%), and H represents the height of the image from the optical axis when the incidence angle ω is 60 degrees.