| 摘要 |
PURPOSE:To obtain the lens which may be used for information reading from a video disc or the like, is wide in information read range and is inexpensive by reducing its size and weight, increasing its working distance, increasing its numerical aperture and maintaining a high resolving power. CONSTITUTION:This is constituted by a concave or convex meniscus lens 1 being the 1st group of which the concave face is directed to the image side, a biconvex lens 2 being the 2nd group, a concave meniscus lens 3 being the 3rd group of which the concave face on the stronger side is directed to the 2nd group, and a convex meniscus lens 4 being the 4th group of which the convex face is directed to the 3rd group by leaving some air spacing. Various conditions based on formulas 1-9 are satisfied. The formulas 1-4 are the conditions necessary for distributing the diopters of the respective lenses, the formula 5 is the conditions necessary for maintaining the working distance long, the formulas 3, 6, 7 are spherical aberration and sinewave conditions, and the formulas 8, 9 negate and balance the astigmatisms produced in the 2nd group. Here, (f) in the formulas is the combined focal length of the lenses, R1-R7 are the radii of curvature, D1, D5 are the central thicknesses of the lenses, D2, D4, D6 are axial spacings and N is refractive index. |
