| 摘要 |
An aspherical single lens which has first and second surfaces both comprising aspherical surfaces represented by the following equation, and which meets the following conditions (1), (2) and (3), wherein a distance from any arbitrary point on either aspherical surface to a plane tangential to an apex of the aspherical surface is X, a distance from the arbitrary point to the optical axis is H, the radius of reference curvature of the nu -th surface (i.e., the radius of curvature of the apex) is R nu , a conical constant of the nu -th surface is K nu , and the aspherical coefficient of the nu -th surface is A nu i (i=3, 4, . . . ): <IMAGE> ( nu = 1, 2) <IMAGE> <IMAGE> <IMAGE> where F is the focal length of the aspherical single lens, D is a thickness of the aspherical single lens along the optical axis, and N is an index of refraction of the aspherical single lens for the particular wavelength of light used with said lens. The present aspherical single lens can satisfactorily correct aberration in both on-axis and off-axis regions through a parallelepiped plate having a thickness of about 0.04 F-0.111 F. An optical head of optical information recording reproducers such as optical card recording reproducers can be reduced in weight and size by utilizing the aspherical single lens of the present invention as an objective or as a collimating lens.
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