A lens system including: a first lens group having a positive refractive power; a second lens group having a positive refractive power; and a third lens group having a positive or negative refractive power, wherein the first lens group comprises four or less lenses, and the first through third lens groups are movable, independently, during focusing and have magnifications in a range from −1 to 0.
1. A lens system consisting of:
a first lens group having a positive refractive power;
a second lens group having a positive refractive power; and
a third lens group having a positive or negative refractive power,
wherein the first lens group comprises four or less lenses,
wherein the first through third lens groups are movable, independently along an optical axis, during focusing,
wherein the lens system has magnification in a range from −1 to 0, and
wherein the third lens group satisfies the following Equation
0.25
≤
Δ
d
3
f
≤
0.8
where Δd 3 is the amount of movement of the third lens group, and f is the focal length of the overall lens system.
2. The lens system of claim 1 , further comprising an aperture stop disposed between the first lens group and the second lens group.
3. The lens system of claim 1 , wherein the third lens group has a refractive index according to the following Equation
1.65≦n d ≦2.0
where n d is the refractive index at d-line of the material used in the third lens group.
4. The lens system of claim 1 , wherein the second lens group comprises doublet or triplet cemented lenses.
5. A lens system comprising:
a first lens group having a positive refractive power;
a second lens group having a positive refractive power; and
a third lens group having a positive or negative refractive power,
wherein the first through third lens groups are movable, independently along an optical axis, during focusing,
wherein the lens system is configured to provide magnifications covering an entire range from −1 to 0 and satisfies the following Equation
0.4
≤
f
2
f
1
≤
0.6
where f 1 is the focal length of the first lens group, and f 2 is the focal length of the second lens group, and
wherein the third lens group satisfies the following Equation
0.25
≤
Δ
d
3
f
≤
0.8
where Δd a is the amount of movement of the third lens group, and f is the focal length of the lens system.
6. The lens system of claim 5 , further comprising an aperture stop disposed between the first lens group and the second lens group.
7. The lens system of claim 5 , wherein the third lens group has a refractive index according to the following Equation
1.65≦n d ≦2.0
where n d is the refractive index at d-line of the material used in the third lens group.
8. The lens system of claim 5 , wherein the second lens group comprises doublet or triplet cemented lenses.
9. A lens system comprising:
a first lens group having a positive refractive power;
a second lens group having a positive refractive power; and
a third lens group having a positive or negative refractive power,
wherein the first lens group comprises four or less lenses,
wherein the first through third lens groups are movable, independently along an optical axis, during focusing,
wherein the lens system has magnification in a range from −1 to 0
wherein the third lens group satisfies the following Equation
0.25
≤
Δ
d
3
f
≤
0.8
where Δd a is the amount of movement of the third lens group, and f is the focal length of the overall lens system, and
wherein the first lens group and the second lens group satisfy the following Equation
0.4
≤
f
2
f
1
≤
0.6
where f 1 is the focal length of the first lens group, and f 2 is the focal length of the second lens group.