| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a zoom lens with improved immediacy of focusing by having a composition of a focusing lens group be as small as possible and with the least number of lenses while having high variable power ratio. <P>SOLUTION: A first lens group G<SB POS="POST">1</SB>is composed of three or more lenses, a third lens group G<SB POS="POST">3</SB>is composed of a 3a lens group G<SB POS="POST">3a</SB>including positive and negative lenses and a 3b lens group G<SB POS="POST">3b</SB>including positive and negative lenses in this order from an object side to an image side, a fourth lens group G<SB POS="POST">4</SB>is composed of two pieces of lenses or less. In this case, a following conditional expression (1) and a condition expression (2) are satisfied by moving the first lens group G<SB POS="POST">1</SB>when varying power from a wide angle end to a telephoto end. -0.8<f<SB POS="POST">4</SB>/f<SB POS="POST">W</SB><-0.3... (1) 0.1<d<SB POS="POST">G3</SB>/L<SB POS="POST">W</SB><0.4... (2) when f<SB POS="POST">W</SB>is a focal distance for a total zoom lens system in the wide angle end, f<SB POS="POST">4</SB>is the focal distance for the fourth lens group G<SB POS="POST">4</SB>, d<SB POS="POST">G3</SB>is thickness of the third lens group G<SB POS="POST">3</SB>on an optical axis, and L<SB POS="POST">W</SB>is the total length of the total zoom lens system in the wide angle end. <P>COPYRIGHT: (C)2013,JPO&INPIT</p> |
