| 摘要 |
PURPOSE:To obtain a compact macro-lens improved at its performance at equal power, efficiently corrected mainly at its spherical aberration and reduced at its extruding distance at the time of focusing by constituting the macro-lens of the 1st group having positive refractive power, the 2nd group having positive refractive power and the 3rd group having negative refractive power arranged successively from the object side. CONSTITUTION:The macro-lens is constituted of the 1st group G1 having positive refractive power, the 2nd group G2 having positive refractive power and the 3rd group G3 having negative refractive power arranged successively from the object side. The 1st group G1 is arranged in the front of an iris, the 2nd group G2 is arranged on the back of the iris and the 3rd group G3 is arranged on the back of the 2nd group G2. At the time of focusing from an infinite-point to equal power, the interval between the 1st and 2nd groups G1, G2 is simply increased up to the intermediate power and then reduced, so that the variation of spherical aberration is reduced and excellent performance can be obtained up to the equal power position.
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