Patent ID: 6650487
Filing Date: 2003-11-18
Classification: G02B

Abstract:
A color image readout lens comprising four lens groups of positive, positive or negative, negative, and positive refractive power, respectively, in order from the object side, as follows:a first lens group formed of only a single lens element, said single lens element having a convex surface on the object side; a second lens group formed of, in order from the object side, a biconvex lens element that is cemented to a biconcave lens element; a stop; a third lens group formed of, in order from the object side, a fourth lens element that is cemented to a fifth lens element, with the fifth lens element having positive refractive power and a convex surface on the image side; and a fourth lens group formed of a single lens element having a convex surface on the image side; wherein the following Conditions (1) to (6) are satisfied33i<45â€ƒâ€ƒCondition (1) âˆ’0.012i0.0006iÂ·&dgr;&thgr;i<<0.0020â€ƒâ€ƒCondition (3) n2>n3â€ƒâ€ƒCondition (4) 52âˆ’&ngr;3<15â€ƒâ€ƒCondition (5) 0.02D6âˆ’D5)/f<0.08â€ƒâ€ƒCondition (6) where&ngr;i is the Abbe number of the ith lens element, in order from the object side, with i=3, 4; &dgr;&thgr;i is the anomalous dispersion of the ith lens element, in order from the object side, with i=3,4; &Sgr;&phgr;iÂ·&dgr;&thgr;i represents the sum of the products of the refractive power and anomalous dispersion of the ith lens elements, in order from the object side, with i=3, 4; n2 is the refractive index of the second lens element, in order from the object side; n3 is the refractive index of the third lens element, in order from the object side; and &ngr;2 is the Abbe number at the d line of the second lens element, in order from the object side, &ngr;3 is the Abbe number at the d line of the third lens element, in order from the object side, D5 is the distance between the third lens element, in order from the object side, and the stop, and D6 is the distance between the stop and the fourth lens element, in order from the object side.