| 摘要 |
<p>A reproducing objective lens for videodiscs for which the working distance is large, the flatness of field is high, resolving power is high and further, the objective lens is so corrected as to compensate for aberrations introduced by additional elements fixed in the optical path and occurring in the long conjugate of the objective lens. For the objective lens, according to the present invention, the Gauss-type lens configuration is adopted as it is easier to obtain a large working distance and high flatness of field with the Gauss-type lens configuration. The objective lens for videodiscs, according to the present invention, is a modified Gauss-type lens system comprising five single lenses, i.e., a first, second, third, fourth and fifth lens. The first lens is a positive lens with its planar surface positioned toward the object side, the second lens is a positive lens, the third lens is a negative meniscus lens with its convex surface positioned toward the object side, the fourth lens is a negative meniscus lens with its concave surface positioned toward the object side and the fifth lens is a positive meniscus lens with its concave surface positioned toward the object side. Further, the objective lens for videodiscs of the present invention satisfies the following conditions when reference symbol f represents the focal length of the lens system as a whole. Reference symbol f3 represents the focal length of the third lens. Reference symbol f4 represents the focal length of the fourth lens. Reference symbol r6 represents the radius of curvature of the surface on the image side of the third lens. Reference symbol r7 represents the radius of curvature of the surface on the object side of the fourth lens. Reference symbol d represents the thickness of the first lens and reference symbol d5 represents the thickness of the third lens. 1. 0.30 .DELTA. r6/f ? 0.23 2. 0.25 ? d1/f ? 0.l5 3. 1.4 ? r6 ¦r7¦? 0.9 4. 6.0 ? f3¦/¦ f4 ? 2.5 5. 0.31 ? d5/f ? 0.21</p> |
