| 摘要 |
PURPOSE:To execute focusing under a satisfactory aberration correction up to a short distance by moving in a small extent by moving the second and fourth groups to the side of an image, in a lens system consisting of 4 groups of positive, negative, positive and negative. CONSTITUTION:A lens system is constituted of a total of 4 groups consisting of the first, second, third and fourth groups having positive, negative, positive and negative refractive power, in order of the side of an object, and is constituted so that ¦f'¦>=2f is satisfied when a focal distance of the whole system, and also a composite focal distance, in case of infinitely distant focusing are made (f) and f', respectively, and also so that focusing is executed by moving the second and fourth groups to the side of the image, against the first and third groups. It is desirable to design so that absolute values of the sum S and C of Seidel factor of each surface of the spherical surface and coma aberration of the first group in case of f=1 become <=0.5. |
