| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-performance telephotographic conversion lens constituted so that the increase of a secondary spectrum is suppressed to the utmost, a monochromatic aberration such as spherical aberration, coma aberration, astigmatism and distortion aberration is excellently corrected and the deterioration of image quality is reduced without making the correction of the chromatic aberration of a principal lens unbalance. SOLUTION: This telephotographic conversion lens consists of, in order from the object side, the positive joined lens of a 1st convex lens L1 and a 2nd concave lens L2, a 3rd convex lens L3 whose convex surface having strong curvature facing an object side and negative joined lens of a 4th convex lens L4 and a 5th concave lens L5. When angular magnification is set to be about 1.35 to 3, an equivalent Abbe number from an (i)th lens to a (j)th lens is defined as (νi, j) and deviation from the standard line of the partial dispersion ratio of the (i)th lens in the kind of nitrate is defined asΔPi, the respective conditions of -0.01<1/ν1.3<0.01, -0.01<1/ν4.5<0.01, 0.003<(ΔP1+ΔP3)/2 andΔP2<0.014 are satisfied.
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