| 摘要 |
PROBLEM TO BE SOLVED: To simplify lens constitution, and a zooming driving part and improve aberration, and further to suppress the extended amount of a lens in focusing in an image-formation variable power optical system and an imaging apparatus. SOLUTION: The image-formation variable power optical system is constituted of three groups having negative, positive and positive refractive power. The first group G<SB>1</SB>comprises a negative lens L<SB>1</SB>and a positive lens L<SB>2</SB>, the second group G<SB>2</SB>comprises a positive lens L<SB>3</SB>, a negative lens L<SB>4</SB>and a lens for correcting aberration L<SB>5</SB>, and the third group G<SB>3</SB>comprises a lens for correcting aberration L<SB>6</SB>. The first group G<SB>1</SB>and the second group G<SB>2</SB>are moved independently in zooming, and the first group G<SB>1</SB>and the second group G<SB>2</SB>are moved integrally in focusing. The optical system satisfies following expressions 1 to 3. The expression 1 is Ng2>1.6, the expression 2 isνg2<29 and the expression 3 is TL/YIM<11.0 (provided that Ng2: refractive index of the second lens L<SB>2</SB>,νg2: Abbe number of the second lens L<SB>2</SB>, TL: maximum entire length of the lens system and YIM: image height (length of half of a diagonal)). COPYRIGHT: (C)2007,JPO&INPIT
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