| 摘要 |
PURPOSE:To obtain an optical head of desired numerical aperture and working distance at all times by setting an interval between a lens contact surface and an object side end face of a lens frame, and a diameter of a diaphragm accordingly, even if an optical characteristic of a refractive index distribution lens to be fitted is varied. CONSTITUTION:In accordance with a focal distance f', a working distance WD', a center wall thickness (d) and a radius of curvature R, of a refractive index distribution lens 1 to be fitted, desired numerical aperture NA and working distance WD are obtained from equations I, II. Values of (a) and (l) are derived, respectively, a diaphragm 5 is worked so that these (a) and (l) are obtained, and thereafter, the refractive index distribution lens 1 is fitted by making its curved surface 1a abut on a lens contact surface 5a. In this way, when (a) and (l) of a lens frame 2 are set in accordance with an optical characteristic of the refractive index distribution lens 1 to be fitted, an optical head of desired numerical aperture NA and working distance WD can be obtained without being influenced by a variation of its optical characteristic.
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