| 摘要 |
PROBLEM TO BE SOLVED: To make a lens optical system compact in terms of aberrational aspect by providing a 3rd group with a diffraction grating in the lens optical system performing zooming by changing a distance between a 1st group and a 2nd group. SOLUTION: The zoom lens is equipped with the 1st group Gr1 having positive power, the 2nd group Gr2 having negative power and the 3rd group Gr3 having positive power in order from an object side, and is constituted to perform the zooming by changing the distance between the 1st group Gr1 and the 2nd group Gr2. A diaphragm S moving for zooming with the 3rd group Gr3 is arranged between the 2nd group Gr2 and the 3rd group Gr3, and a low-pass filter LPF is arranged on a side nearest to an image surface I. The 3rd group Gr3 is constituted of a biconvex positive lens and a negative meniscus lens which is concave to the object side and is provided with the diffraction grating on the II surface (r11). In order to make this optical system compact, it is effective to use the diffraction grating in the 3rd group Gr3 in terms of compensating the aberration.
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