Patent ID: 6288820
Filing Date: 2001-09-11
Classification: G02B

Abstract:
An image scanning lens for a scanning unit, said image scanning lens formed of, in order from the object side, only four lens elements having refractive power as follows:a first lens element of positive refractive power and meniscus shape having its convex surface on the object side;a second lens element of negative refractive power that is biconcave;a third lens element of positive refractive power that is biconvex; anda fourth lens element of negative refractive power having a concave surface on the object side;wherein the following conditions are satisfied:0.09.ltoreq.DR.sub.3 /f.ltoreq.0.200.40.ltoreq..vertline.f.sub.4 /f.vertline..ltoreq.1.30.nu..sub.4.gtoreq.36.00.31.ltoreq..SIGMA.D.sub.i /f.ltoreq.0.48DR.sub.3-4 /f.ltoreq.0.07whereDR.sub.3 is the on-axis thickness of the third lens element, in order from the object side;f is the focal length of the image scanning lens;f.sub.4 is the focal length of the fourth lens element, in order from the object side;.nu..sub.4 is the Abbe number of the fourth lens element, in order from the object side;.SIGMA.D.sub.i is the overall length of the image scanning lens; andDR.sub.3-4 is the on-axis spacing between the third lens element and the fourth lens element, in order from the object side.