Reading lens system for use in scanner

A reading lens system for a scanner, used at a reduced magnification so as to read an original image at a high speed and comprising, successively in order from an object toward an image:

• (a) a first lens unit including a positive lens serving as a first lens and a negative lens serving as a second lens and being cemented on the image side of said first lens;
• (b) a second lens unit including a meniscus lens serving as a third lens having a convex surface facing the object;
• (c) a third lens unit including a meniscus lens serving as a fourth lens having a convex surface facing the image;
• (d) a fourth lens unit including a double-concave lens serving as a fifth lens and a double-convex lens serving as a sixth lens and being cemented on the image side of said fifth lens;
• (e) a fifth lens unit including a plane-parallel glass plate serving as a seventh lens;
• and
• (f) an aperture disposed between said second lens unit and said third lens unit,
• said reading lens system meeting the following conditions:
• 1.01<f/f.sub.12 <1.05 (1-I)
• 0.02<n.sub.2 -n.sub.1 ( 1-II)
• where f is the focal length of the entire reading lens system;
• f.sub.12 is the focal length of said first lens unit;
• and n.sub.1, n.sub.2 are refractive indices of material composing the first lens and the second lens.