US 7,595,936 B2
Zoom lens system and camera having the same
Koji Hoshi, Yokohama (Japan)
Assigned to Canon Kabushiki Kaisha, Tokyo (Japan)
Filed on Apr. 24, 2008, as Appl. No. 12/108,734.
Claims priority of application No. 2007-115085 (JP), filed on Apr. 25, 2007.
Prior Publication US 2008/0266673 A1, Oct. 30, 2008
Int. Cl. G02B 15/14 (2006.01)
U.S. Cl. 359—687 12 Claims
OG exemplary drawing
 
1. A zoom lens system, in that order from an object side to an image side, comprising:
a first lens unit having a positive optical power;
a second lens unit having a negative optical power;
a third lens unit having a positive optical power, the third lens unit including a first lens subunit having a negative optical power, and a second lens subunit having a positive optical power, in that order from the object side to the image side; and
a fourth lens unit having a positive optical power, the fourth lens unit including at least a positive lens element,
wherein the second and fourth lens units move along an optical axis during zooming,
wherein the first lens subunit has no more than a positive lens element and a negative lens element,
wherein the second lens subunit has no more than a positive lens element and a negative lens element, and
wherein the following conditional expressions are satisfied:
0.21<3aNn−3bPn
0.07<4Pn−3bPn
where 3aNn is a refractive index of a material of the negative lens element in the first lens subunit, 3bPn is a refractive index of a material of the positive lens element in the second lens subunit, and 4Pn is a refractive index of a material having the highest refractive index in a material of the positive lens element included in the fourth lens unit.