Miniature zoom lens
View Patent ↗A miniature zoom lens has, sequentially from an object side, a first lens group G 1 having negative refractive power, a second lens group G 2 having positive refractive power and including a diaphragm, and a third lens group G 3 having positive refractive power. The first lens group G 1 is formed from a single negative lens L 1 . The second lens group G 2 is formed from, sequentially from the object side, a single positive lens L 2 and a single negative lens L 3. The third lens group G 3 is formed form a single positive lens L 4 . The first lens group G 1 is immovable and the second lens group G 2 and the third lens group G 3 move in an optical axis direction at variable power. The miniature zoom lens provides a large zoom ratio while keeping a constant total length.
1. A miniature zoom lens, comprising, sequentially from an object side toward an image forming side:
a first lens group having negative refractive power,
a second lens group having positive refractive power and including a diaphragm, and
a third lens group having positive refractive power;
wherein:
said first lens group comprises a single negative lens;
said second lens group comprises, sequentially from the object side, a single positive lens and a single negative lens;
said third lens group comprises a single positive lens;
said first lens group is immovable;
said second lens group and said third lens group move in an optical axis direction at variable power;
the negative lens of said first lens group is a meniscus lens having at least one aspherical surface, and a respective largest curvature surface facing the object side;
the positive lens of said second lens group includes at least one aspherical surface, and the negative lens of said second lens group includes at least one aspherical surface; and
the positive lens of said third lens group has a respective largest curvature surface facing the image-forming side.
2. The miniature zoom lens according to claim 1 , wherein:
the positive lens of said second lens group is a biconvex lens;
the negative lens of said second lens group is a negative meniscus lens; and
the positive lens of said third lens group is a positive meniscus lens.
3. The miniature zoom lens according to claim 2 , wherein the following conditional expression (1) is satisfied:
2.5<| F 1 |/F W <3.0 (1)
where F1 is a focal length (mm) of the first lens group, and F w is a focal length (mm) of an overall lens system at a wide angle end.
4. The miniature zoom lens according to claim 2 , wherein the following conditional expression (2) is satisfied:
1.0<| F 2 |/F W <1.5 (2)
where F 2 is a focal length (mm) of the second lens group, and F w is a focal length (mm) of an overall lens system at a wide angle end.
5. The miniature zoom lens according to claim 2 , wherein the following conditional expressions (1) and (2) are satisfied:
2.5<| F 1 |/F W <3.0 (1)
1.0<| F 2 |/F W <1.5 (2)
where F 1 is a focal length (mm) of the first lens group, F 2 is a focal length (mm) of the second lens group, and F w is a focal length (mm) of an overall lens system at a wide angle end.