| 摘要 |
PROBLEM TO BE SOLVED: To make an image input device smaller in size, lower in cost, higher in resolution and higher in reading speed by making it possible to embody an excellent reducing lens which is highly made wider in angle, lower in cost, higher in resolution and larger in aperture ratio. SOLUTION: The reducing lens 1 is constituted by successively arranging first to fourth lens groups from an object side (left side) toward an image side (right side). The first lens group is composed of a cemented lens of a positive meniscus lens of which the concave face is directed to the object side and a negative meniscus lens of which the convex face is directed to the object side. The second lens group is composed of the negative meniscus lens of which the convex face is directed to the object side. The third lens group is composed of the negative meniscus lens of which the concave face is directed to the object side. The fourth lens group is composed of the cemented lens of the negative meniscus lens of which the concave face is directed to the object side and the positive meniscus lens of which the convex face is directed to the object side. The conditions of the equation are satisfied when the radius of curvature on the object side of the third lens group is defined as r7, the radius of curvature on the image side as r8, the surface separation which is a lens center thickness as d7 and the focal length of the entire system as (f).
|
