Zoom lens and electronic still camera using the same

A zoom lens comprising a first lens group with a negative power, a second lens group with a positive power to whose object side an aperture stop has been fixed, and a third lens group with a positive power, arranged in that order from an object side to an image plane side;

• wherein said first lens group comprises a first lens that is a negative meniscus lens whose surface with strong curvature is facing the image plane side, and a second lens that is a positive lens whose surface with strong curvature is facing the object side, arranged in that order from the object side;
• wherein said second lens group comprises a third lens that is a positive lens whose surface with strong curvature is facing the object side, a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens, arranged in that order from the object side;
• wherein said third lens group comprises a seventh lens that is a positive lens;
• wherein the image plane side surface of said first lens and the object side surface of said third lens are aspherical surfaces whose local radius of curvature is monotonically increased as distance from the center increases;
• wherein one of the surfaces of said seventh lens is an aspherical surface;
• wherein when zooming from a wide-angle end to a tele end when an object distance is ∞, said first lens group retreats to the image plane side and then moves toward the object side and said second lens group moves monotonically toward the object side;
• and
• wherein when LW is a length from an apex of the object side surface of said first lens to the image plane at the wide-angle end, LT is a length from the apex of the object side surface of said first lens to the image plane at the tele end, fW is a combined focal length of the entire lens system at the wide-angle end at an object distance of ∞, fG2 is a combined focal length of said second lens group, fG3 is a combined focal length of said third lens group, fi is a focal length of said i-th (i is a natural number) lens, ni is a refractive index of said i-th lens, and νi is the Abbe number of said i-th lens, then conditional expressions
• |LW−LT|/LW<0.1 (1)
• 1.9<fG2/fW<2.4 (2)
• 3.2<fG3/fW<4.0 (3)
• 0.6<f3/fG2<1.1 (4)
• 1.5<f6/fG2<1.8 (5)
• n3>1.75 (6)
• ν3>35 (7)
• n4>1.6 (8′)
• ν4>45 (9)
• n6>1.7 (10)
• 35<ν6<50 (11)
• are satisfied, a zoom ratio is ×2.5 to ×3.2 if the object distance is ∞, and a field angle at the wide-angle end is 60° to 70°.

A zoom lens comprising a first lens group with a negative power, an aperture stop, a second lens group with a positive power, and a third lens group with a positive power, arranged in that order from an object side to an image plane side;

• wherein said first lens group comprises a first lens that is a negative lens whose surface with strong curvature is facing the image plane side, and a second lens that is a positive lens whose surface with strong curvature is facing the object side, arranged in that order from the object side;
• wherein said second lens group comprises a third lens that is a positive lens whose surface with strong curvature is facing the object side, a fourth lens that is a positive lens, a fifth lens that is a negative lens, and a sixth lens that is a positive lens, arranged in that order from the object side, and also can be parallel displaced in a direction perpendicular to an optical axis;
• wherein said third lens group comprises a seventh lens that is a positive lens;
• wherein when zooming from a wide-angle end to a tele end when an object distance is ∞, said first lens group retreats to the image plane side and then moves toward the object side and said second lens group moves monotonically toward the object side;
• and
• wherein when fW is a combined focal length of the entire lens system at the wide-angle end at an object distance of ∞, fG2 is a combined focal length of said second lens group, and mG2T and mG3T are magnifications of said second lens group and said third lens group, respectively, at the tele end at an object distance of ∞, then conditional expressions
• 1.9<fG2/fW<2.4 (2)
• 1.7<(1−mG2T)mG3T<2.1 (15)
• are satisfied, a zoom ratio is ×2.5 to ×3.2 if the object distance is ∞, and a field angle at the wide-angle end is 60° to 70°.