Imaging lens and imaging apparatus
An imaging lens and imaging apparatus are disclosed. In one example, an imaging lens includes a first lens group having positive refractive power, a second lens group having a positive refractive power, and a third lens group having positive or negative refractive power, the first lens group being fixed with respect to an image plane, the second lens group traveling along an optical axis to the object side, and the third lens group being fixed with respect to the image plane. The first lens group may include two positive lenses and a negative lens. The second lens group may include a second a-lens component having negative refractive power and a second b-lens component having positive refractive power. The third lens group may include a third a-lens component having positive refractive power and a third b-lens component having negative refractive power.
1. An imaging lens comprising: in order from object side toward image plane side, a first lens group having positive refractive power; a second lens group having a positive refractive power; and a third lens group having positive or negative refractive power,
the first lens group being fixed with respect to an image plane, the second lens group traveling along an optical axis to the object side, and the third lens group being fixed with respect to the image plane, upon focusing from an object at infinity to an object at a short distance,
the first lens group including, in order from the object side toward the image plane side, at least two positive lenses that are disposed closest to the object side in the first lens group and a negative lens that is disposed closest to the image plane side in the first lens group,
the second lens group including, in order from the object side toward the image plane side, a second a-lens component having negative refractive power and a second b-lens component having positive refractive power, and
the third lens group including, in order from the object side toward the image plane side, a third a-lens component having positive refractive power and a third b-lens component having negative refractive power,
a following conditional expression is satisfied:
−1.5< f 1/ f 3<0.2 (4A)
where a focal length of the first lens group is f1, and a focal length of the third lens group is f3.
2. The imaging lens according to claim 1 , wherein
the third b-lens component includes a single negative lens, and
a following conditional expression is satisfied:
−10<( r 1+ r 2)/( r 1− r 2)<0.0 (2)
where a radius of curvature of the third b-lens component on the object side is r 1 , and a radius of curvature of the third b-lens group on the image plane side is r 2 .
3. The imaging lens according to claim 1 , wherein
the second b-lens component includes a cemented lens having, in order from the object side toward the image plane side, a negative lens and a positive lens, and
a following conditional expression is satisfied:
0< f 2 b/f 2<1.6 (3)
where a focal length of the second lens group is f2, and a focal length of the second b-lens component is f2b.
4. The imaging lens according to claim 1 , wherein the third a-lens component includes a cemented lens having, in order from the object side toward the image plane side, a positive lens and a negative lens.
5. The imaging lens according to claim 1 , wherein the second lens group has an aspherical shape that has a positive refractive effect with respect to an on-axis bundle of rays and in which the positive refractive effect becomes weak toward a periphery of an effective aperture.
6. The imaging lens according to claim 1 , wherein
the second a-lens component includes a cemented lens having, in order from the object side toward the image plane side, a negative lens and a positive lens, and
a following conditional expression is satisfied:
−35< f 2 a/f 2<−4 (5)
where a focal length of the second lens group is f2, and a focal length of the second a-lens component is f2a.
7. The imaging lens according to claim 1 , wherein
the second b-lens component includes, in order from the object side toward the image plane side,
the second b-lens component includes, in order from the object side toward the image plane side, a second b1-lens component and a second b2-lens component, and
a following conditional expression is satisfied:
0< f 2 b 2/ f 2 b 1<5 (6)
where a focal length of the second b1-lens component is f2b1, and a focal length of the second b2-lens component is f2b2.
8. The imaging lens according to claim 1 , wherein a following conditional expression is satisfied:
−1.5< f 2 b/f 2 a< 0.0 (7)
where a focal length of the second a-lens component is f2a, and a focal length of the second b-lens component is f2b.
9. The imaging lens according to claim 1 , wherein a following conditional expression is satisfied:
−1< r _2 a/f<− 0.1 (8)
where a radius of curvature of a surface positioned closest to the object side, of the second a-lens component is r_ 2 a, and a focal length of a system as a whole is f.
10. The imaging lens according to claim 1 , wherein a lens surface positioned closest to the object side of the second lens group has a concave shape on the object side.
11. An imaging lens comprising: in order from object side toward image plane side, a first lens group having positive refractive power; a second lens group having a positive refractive power; and a third lens group having positive or negative refractive power,
the first lens group being fixed with respect to an image plane, the second lens group traveling along an optical axis to the object side, and the third lens group being fixed with respect to the image plane, upon focusing from an object at infinity to an object at a short distance,
the first lens group including, in order from the object side toward the image plane side, at least two positive lenses and a negative lens that is disposed closest to the image plane side in the first lens group,
the second lens group including, in order from the object side toward the image plane side, a second a-lens component having negative refractive power and a second b-lens component having positive refractive power, and
the third lens group including, in order from the object side toward the image plane side, a third a-lens component having positive refractive power and a third b-lens component having negative refractive power,
a following conditional expression is satisfied:
−1.5< f 1/ f 3<0.2 (4A)
where a focal length of the first lens group is f1, and a focal length of the third lens group is f3, and wherein a following conditional expression is satisfied:
−1.6< f 3 b/f 3 a< 0 (1)
where a focal length of the third a-lens component is f3a, and a focal length of the third b-lens component is f3b.
12. An imaging apparatus with an imaging lens and an imaging device that outputs an imaging signal corresponding to an optical image formed by the imaging lens, the imaging lens comprising:
in order from object side toward image plane side, a first lens group having positive refractive power; a second lens group having a positive refractive power; and a third lens group having positive or negative refractive power;
the first lens group being fixed with respect to an image plane, the second lens group traveling along an optical axis to the object side, and the third lens group being fixed with respect to the image plane, upon focusing from an object at infinity to an object at a short distance;
the first lens group including, in order from the object side toward the image plane side, at least two positive lenses that are disposed closest to the object side in the first lens group and a negative lens that is disposed closest to the image plane side in the first lens group;
the second lens group including, in order from the object side toward the image plane side, a second a-lens component having negative refractive power and a second b-lens component having positive refractive power; and
the third lens group including, in order from the object side toward the image plane side, a third a-lens component having positive refractive power and a third b-lens component having negative refractive power,
a following conditional expression is satisfied:
−1.5< f 1/ f 3<0.2 (4A)
where a focal length of the first lens group is f1, and a focal length of the third lens group is f3.
13. The imaging apparatus according to claim 12 , wherein a following conditional expression is satisfied:
−1.6< f 3 b/f 3 a< 0 (1)
where a focal length of the third a-lens component is f3a, and a focal length of the third b-lens component is f3b.
14. The imaging apparatus according to claim 12 , wherein
the third b-lens component includes a single negative lens, and
a following conditional expression is satisfied:
−10<( r 1+ r 2)/( r 1− r 2)<0.0 (2)
where a radius of curvature of the third b-lens component on the object side is r 1 , and a radius of curvature of the third b-lens group on the image plane side is r 2 .
15. The imaging apparatus according to claim 12 , wherein
the second b-lens component includes a cemented lens having, in order from the object side toward the image plane side, a negative lens and a positive lens, and
a following conditional expression is satisfied:
0< f 2 b/f 2<1.6 (3)
where a focal length of the second lens group is f2, and a focal length of the second b-lens component is f2b.
16. The imaging apparatus according to claim 12 , wherein the third a-lens component includes a cemented lens having, in order from the object side toward the image plane side, a positive lens and a negative lens.
17. The imaging apparatus according to claim 12 , wherein the second lens group has an aspherical shape that has a positive refractive effect with respect to an on-axis bundle of rays and in which the positive refractive effect becomes weak toward a periphery of an effective aperture.
18. The imaging apparatus according to claim 12 , wherein
the second a-lens component includes a cemented lens having, in order from the object side toward the image plane side, a negative lens and a positive lens, and
a following conditional expression is satisfied:
−35< f 2 a/f 2<−4 (5)
where a focal length of the second lens group is f2, and a focal length of the second a-lens component is f2a.
19. The imaging apparatus according to claim 12 , wherein
the second b-lens component includes, in order from the object side toward the image plane side,
the second b-lens component includes, in order from the object side toward the image plane side, a second b1-lens component and a second b2-lens component, and
a following conditional expression is satisfied:
0< f 2 b 2/ f 2 b 1<5 (6)
where a focal length of the second b1-lens component is f2b1, and a focal length of the second b2-lens component is f2b2.
20. The imaging apparatus according to claim 12 , wherein
a following conditional expression is satisfied:
−1.5< f 2 b/f 2 a< 0.0 (7)
where a focal length of the second a-lens component is f2a, and a focal length of the second b-lens component is f2b.