| 摘要 |
PROBLEM TO BE SOLVED: To obtain a lens for reading an original where various kinds of aberration are compensated with good balance and which has high resolving power and is suitable for digital reading equipment while keeping FNo showing a bright state and a numerical aperture being 100% to a peripheral viewing angle by appropriately setting the lens constitution of respective lens groups. SOLUTION: This lens is provided with four lens groups, that is, a 1st group G1 to a 4th group G4. In the case of setting respective parameters P1=(dG2+dG 3)/(d1+d10), P2=(n1+n2+n5+n6)/4-(n3+n4)/2, 3P=(f1/f)/n1+(f6/f)n6, P4=((f1/f12)×(d3+d4))/((f4/f34)×(d7+d8)), P5=(ν1+ν2+ν5+ν6)/4-(ν3+ν4)/2, the lens satisfies conditions 1.3<P1<1.9, 0.02<P2<0.04, 1.1<P3<1.3, 0.9<P4<2.1 and 15<P5<20. Thus, various kinds of aberration are compensated with good balance and the lens has the high resolving power.
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