Macro lens system
View Patent ↗A macro lens system includes a positive first lens group, a diaphragm, a positive second lens group, and a negative third lens group. Upon focusing from an object at an infinite distance to an object at a closer distance, the positive first lens group and the positive second lens group integrally move toward the object without changing a distance therebetween with respect to the negative third lens group which is stationary with respect to an imaging plane in a camera body. The positive first lens group includes a negative first lens sub-lens group and a positive second sub-lens group which are divided at a maximum distance between lens elements in the positive first lens group. The macro lens system satisfies specified conditions.
1. A macro lens system comprises a positive first lens group, a diaphragm, a positive second lens group, and a negative third lens group, in this order from an object,
wherein upon focusing from an object at an infinite distance to an object at a closer distance, said positive first lens group and said positive second lens group integrally move toward the object without changing a distance therebetween, with respect to said negative third lens group which is stationary with respect to an imaging plane in a camera body;
wherein said positive first lens group comprises a negative first sub-lens group and a positive second sub-lens group which are divided at a maximum distance between lens elements in said positive first lens group; and
wherein said a macro lens system satisfies the following conditions:
0.32<d/f<0.7
−10<f3/f<−6
wherein
d designates an distance between said negative first sub-lens group and said positive second sub-lens group;
f designates a focal length of the entire macro lens system; and
f 3 designates a focal length of said negative third lens group.
2. The macro lens system according to claim 1 , wherein said negative first sub-lens group comprises a plurality of lens elements,
wherein said plurality of lens elements comprise a negative lens element;
wherein the rest of said plurality of lens elements are provided on the object-side of said negative lens element; and
wherein said rest of said plurality of lens elements comprise at least one positive lens element.
3. The macro lens system according to claim 2 , wherein said negative first sub-lens group comprises a positive first lens element having a convex surface facing toward the object and a negative second lens element, in this order from the object.
4. The macro lens system according to claim 3 , wherein said negative second lens element comprises a negative meniscus lens element having the concave surface, with a smaller radius of curvature, facing toward the image.
5. The macro lens system according to claim 3 , wherein said positive second sub-lens group comprises cemented lens elements having a positive third lens element and a negative fourth lens element, in this order from the object.
6. The macro lens system according to claim 1 , further satisfying the following condition:
−0.75<f 1b−2 /f1a<−0.55
wherein
f 1b−2 designates a combined focal length of said positive second sub-lens group and said positive second lens group; and
f1a designates a focal length of said negative first sub-lens group.
7. The macro lens system according to claim 6 , wherein said positive second lens group comprises a biconcave negative lens element, and two positive lens elements, in that order from the object.
8. The macro lens system according to claim 7 , wherein said positive second lens group comprises a negative biconcave lens element, a positive lens element having a convex surface facing toward the image, and a positive biconvex lens element, in this order from the object.
9. The macro lens system according to claim 1 , wherein said negative third lens group comprises a negative lens element and a positive biconvex lens element.