Zoom lens system

A zoom lens system comprising, in order from an object:

• a first lens group having positive refractive power;
• a second lens group having negative refractive power;
• a third lens group having positive refractive power;
• and
• a fourth lens group having positive refractive power;
• each lens group being moved to the object side such that when the state of lens group positions of the zoom lens system is changed from a wide-angle end state to a telephoto end state, the separation between the first lens group and the second lens group increases, the separation between the second lens group and the third lens group decreases, and the separation between the third lens group and the fourth lens group decreases;
• the second lens group being composed of four lens elements arranged, in order from the object:
• a negative lens having a concave surface facing to an image side;
• a double concave negative lens;
• a double convex positive lens;
• and
• a negative lens having a concave surface facing to the object side;
• and
• the following conditional expressions being satisfied:
• 3<|f2B|/|f2|<5 (5)
• 0.3<f2P/|f2B|<0.45 (6)
• 0.45<D2W/D1T<0.60 (9)
• where f2B denotes the focal length of the three lenses arranged to the image side in the second lens group which has four lens elements, f2 denotes the focal length of the second lens group, and f2P denotes the focal length of the double convex positive lens arranged in the second lens group, and where D2W denotes the separation along the optical axis between the second lens group and the third lens group in the wide-angle end state, and D1T denotes the separation along the optical axis between the first lens group and the second lens group in the telephoto end state.

A zoom lens system comprising, in order from an object:

• a first lens group having positive refractive power;
• a second lens group having negative refractive power;
• a third lens group having positive refractive power;
• and
• a fourth lens group having positive refractive power;
• each lens group being moved to the object side such that when the state of lens group positions of the zoom lens system is changed from a wide-angle end state to a telephoto end state, the separation between the first lens group and the second lens group increases, the separation between the second lens group and the third lens group decreases, and the separation between the third lens group and the fourth lens group decreases;
• the second lens group being composed of four lens elements arranged, in order from the object:
• a negative lens having a concave surface facing to an image side;
• a double concave negative lens;
• a double convex positive lens;
• and
• a negative lens having a concave surface facing to the object side;
• and
• the following conditional expressions being satisfied:
• 3<|f2B|/|f2|<5 (5)
• 0.3<f2P/|f2B|<0.45 (6)
• where f2B denotes the focal length of the three lenses arranged to the image side in the second lens group which has four lens elements, f2 denotes the focal length of the second lens group, and f2P denotes the focal length of the double convex positive lens arranged in the second lens group;
• and
• wherein the first lens group is composed of three lenses arranged, in order from the object, a negative lens having a convex surface facing to the object side, a first positive lens having a convex surface facing to the object side, and a second positive lens having a convex surface facing to the object side, and wherein the following conditional expression is satisfied:
• 2<f13/f1<4 (8)
• where f13 denotes the focal length of the positive lens arranged to the image side in the first lens group which has two positive lenses, and f1 denotes the focal length of the first lens group.