| 摘要 |
PURPOSE:To offer a lens which has small lens overall length as 2.1F and a sufficient long working distance as 0.6F, and has satisfactorily corrected various aberrations, by constituting a lens system of 4 groups and 4 pieces of lenses, and also satisfying a specific condition. CONSTITUTION:A lens system is constituted of 4 groups and 4 pieces of lenses, the first group is a negative meniscus lens whose concave surface has been turned to a light source side, the second group is a positive lens, the third group is a negative meniscus lens whose concave surface is faced to the light source side, and the fourth group is a convex positive meniscus lens against the light source side. When F, and F1, F2 and F3, and F12, d4 and N4 denote a composite focal distance of the lens system, focal distances of the first, second and third lenses, a composite focal distance up to the second group, an air gap between the second group and the third group, and a refractive index of the fourth group lens, respectively, this lens system is constituted so as to satisfy the conditional inequalities 1-6. In this way, it is possible to obtain a lens system which has small lens overall length as 2.1F, has a long working distance as 0.6, and has satisfactorily corrected various aberrations. |
