| 摘要 |
PROBLEM TO BE SOLVED: To obtain a read lens which is inexpensive and improves the quality of read image while excellently compensating various aberrations and making the lens system compact and wide in field angle by using four lenses which meet specific conditional expressions. SOLUTION: An image forming lens consists of four lenses L1 -L4 and a stop (i) is arranged between the 2nd lens L2 and 3rd lens L3 , and luminous flux which is made incident from an object side along the optical axis is imaged at an image formation position P. Further, those lenses meet the conditional inequalities of 0.87<f(1/R8 -1/R7 )<2.75, 0.23<R1 /f<0.38, and 1.08<|N4 .f4|f<3.70. Here, (f) is the composited focal length of the whole lens system, f4 the focal length of the 4th lens, Ri the radius of curvature of an (i)th surface, and N4 the refractive index of the 4th lens to an (e) line. Consequently, the compact and light lens system which is composed of the four lenses, or compact can be obtained.
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