Image forming lens system and image pickup apparatus including the same
An image forming lens system includes a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit. The first lens unit includes in order from the object side, a front-side lens unit having a positive refractive power and a rear-side lens unit. The second lens unit moves at a time of focusing. The third lens unit has a positive lens element. The rear-side lens unit includes a negative lens element and a positive lens element. The front-side lens unit has an aspherical surface having a positive refractive power on an axis, or the rear-side lens unit has an aspherical surface having a negative refractive power on an axis. The lens element closest to the object side in the first lens unit is fixed in position. Following Conditional Expression (9) is satisfied: 0.06≤| fG 2/ f |≤0.195 (9).
1. An image forming lens system comprising, in order from an object side to an image side:
a first lens unit having a positive refractive power;
a second lens unit having a negative refractive power; and
a third lens unit,
wherein:
the first lens unit includes in order from the object side, a front-side lens unit having a positive refractive power and a rear-side lens unit with an air space interposed therebetween,
the second lens unit moves by changing respective air spaces on the object side and the image side at a time of focusing,
the third lens unit includes a positive lens element,
the rear-side lens unit includes a negative lens element and a positive lens element,
the front-side lens unit has an aspherical surface having a positive refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, or
the rear-side lens unit has an aspherical surface having a negative refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis,
a lens element closest to the object side in the first lens unit is fixed in position, and
the following Conditional Expression (9) is satisfied:
0.06≤| fG 2/ f|≤ 0.195 (9)
where
fG2 is a focal length of the second lens unit,
f is a longest focal length of the entire image forming lens system at a time of focusing to a furthest distance, and
a lens element is a lens having two refractive surfaces which are an object-side surface and an image-side surface, and having no other refractive surface between the two refractive surfaces.
2. An image forming lens system comprising, in order from an object side to an image side:
a first lens unit having a positive refractive power;
a second lens unit having a negative refractive power; and
a third lens unit,
wherein:
the first lens unit includes in order from the object side, a front-side lens unit having a positive refractive power and a rear-side lens unit with an air space interposed therebetween,
the second lens unit moves by changing respective air spaces on the object side and the image side at a time of focusing,
the third lens unit includes a positive lens element,
the rear-side lens unit includes a negative lens element and a positive lens element,
the front-side lens unit has an aspherical surface having a positive refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, or
the rear-side lens unit has an aspherical surface having a negative refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis,
a lens element closest to the object side in the first lens unit is fixed in position,
an aperture stop that restricts on-axis luminous flux is disposed between the first lens unit and the second lens unit, and
the following Conditional Expression (9-1) is satisfied:
0.04≤| fG 2/ f|≤ 0.41 (9-1)
where
fG2 is a focal length of the second lens unit,
f is a longest focal length of the entire image forming lens system at a time of focusing to a furthest distance, and
a lens element is a lens having two refractive surfaces which are an object-side surface and an image-side surface, and having no other refractive surface between the two refractive surfaces.
3. An image forming lens system comprising, in order from an object side to an image side:
a first lens unit having a positive refractive power;
a second lens unit having a negative refractive power; and
a third lens unit,
wherein:
the first lens unit includes in order from the object side, a front-side lens unit having a positive refractive power and a rear-side lens unit with an air space interposed therebetween,
the second lens unit moves by changing respective air spaces on the object side and the image side at a time of focusing,
the third lens unit has a positive lens element,
each lens element in the front-side lens unit is a lens element that satisfies the following Conditional Expression (a),
the rear-side lens unit includes a negative lens element and a positive lens element,
the front-side lens unit has an aspherical surface having a positive refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, or
the rear-side lens unit has an aspherical surface having a negative refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, and
the following Conditional Expression (1) is satisfied:
−0.7≤ f/f Lens (a)
0.015 ≤ΔGFGR/f≤ 0.25 (1)
where
f is a longest focal length of the entire image forming lens system at a time of focusing to a furthest distance,
fLens is a focal length of each lens element in the front-side lens unit,
ΔGFGR is an on-axis air space from an image-side surface in the front-side lens unit to an object-side surface in the rear-side lens unit, and
a lens element is a lens having two refractive surfaces which are an object-side surface and an image-side surface, and having no other refractive surface between the two refractive surfaces.
4. An image forming lens system comprising, in order from an object side to an image side:
a first lens unit having a positive refractive power;
a second lens unit having a negative refractive power; and
a third lens unit,
wherein:
the first lens unit includes in order from the object side, a front-side lens unit having a positive refractive power and a rear-side lens unit with an air space interposed therebetween,
the second lens unit moves by changing respective air spaces on the object side and the image side at a time of focusing,
the third lens unit includes a positive lens element,
each lens element in the front-side lens unit does not include a predetermined negative lens element that satisfies the following Conditional Expression (b),
the rear-side lens unit includes a negative lens element and a positive lens element,
the front-side lens unit has an aspherical surface having a positive refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, or
the rear-side lens unit has an aspherical surface having a negative refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis, and
the following Conditional Expression (1) is satisfied:
0.02≤ DNx/φenp (b)
0.015 ≤ΔGFGR/f≤ 0.25 (1)
where
DNx is a thickness on an optical axis of the predetermined negative lens element,
φenp is a maximum diameter of an entrance pupil of the image forming lens system in a state of achieving a longest focal length at a time of focusing to a furthest distance,
f is a longest focal length of the entire image forming lens system at a time of focusing to a furthest distance,
ΔGFGR is an on-axis air space from an image-side surface in the front-side lens unit to an object-side surface in the rear-side lens unit, and
a lens element is a lens having two refractive surfaces which are an object-side surface and an image-side surface, and having no other refractive surface between the two refractive surfaces.
5. An image forming lens system comprising, in order from an object side to an image side:
a first lens unit having a positive refractive power;
a second lens unit having a negative refractive power; and
a third lens unit,
wherein:
the first lens unit includes in order from the object side, a front-side lens unit having a positive refractive power and a rear-side lens unit with an air space interposed therebetween,
the second lens unit moves by changing respective air spaces on the object side and the image side at a time of focusing,
the third lens unit includes a positive lens element,
the rear-side lens unit includes a negative lens element and a positive lens element,
each lens element in the front-side lens unit is a lens element that satisfies the following Conditional Expression (a), or
each lens element in the front-side lens unit does not include a predetermined negative lens element that satisfies following the Conditional Expression (b), and
the following Conditional Expressions (1), (9-2), and (3″) are satisfied:
−0.7≤ f/f Lens (a)
0.02≤ DNx/φenp (b)
0.015 ≤ΔGFGR/f≤ 0.25 (1)
0.06≤| fG 2/ f|≤ 0.22 (9-2)
77 ≤νdGFave (3″)
where
f is a longest focal length of the entire image forming lens system at a time of focusing to a furthest distance,
fLens is a focal length of each lens element in the front-side lens unit,
DNx is a thickness on an optical axis of the predetermined negative lens element,
φenp is a maximum diameter of an entrance pupil of the image forming lens system in a state of achieving a longest focal length at a time of focusing to a furthest distance,
ΔGFGR is an on-axis air space from an image-side surface in the front-side lens unit to an object-side surface in the rear-side lens unit,
fG2 is a focal length of the second lens unit,
νdGFave is an average Abbe number of positive lens elements in the front-side lens unit, and
a lens element is a lens having two refractive surfaces which are an object-side surface and an image-side surface, and having no other refractive surface between the two refractive surfaces.
6. The image forming lens system according to claim 4 , wherein the predetermined negative lens element is disposed in any lens unit closer to the image side than the front-side lens unit.
7. The image forming lens system according to claim 1 , wherein:
the rear-side lens unit includes a first rear-side lens unit and a second rear-side lens unit with an air space interposed therebetween,
the first rear-side lens unit includes a negative lens element and a positive lens element, and
the second rear-side lens unit includes a positive lens element.
8. The image forming lens system according to claim 1 , wherein the following Conditional Expression (1) is satisfied:
0.015 ≤ΔGFGR/f≤ 0.25 (1)
where
f is the longest focal length of the entire image forming lens system at a time of focusing to a furthest distance, and
ΔGFGR is an on-axis air space from an image-side surface in the front-side lens unit to an object-side surface in the rear-side lens unit.
9. The image forming lens system according to claim 1 , wherein the following Conditional Expression (2) is satisfied:
0.10 ≤DGFoGRo/f ≤0.5 (2)
where
DGFoGRo is a distance from a surface closest to the object side in the front-side lens unit to a surface closest to the object side in the rear-side lens unit, and
f is the longest focal length of the entire image forming lens system at a time of focusing to a furthest distance.
10. The image forming lens system according to claim 1 , wherein the following Conditional Expression (3) is satisfied:
72 ≤νdGFave (3)
where
νdGFave is an average Abbe number of positive lens elements in the front-side lens unit, and
a lens element is a lens having two refractive surfaces, namely, an object-side surface and an image-side surface and having no other refractive surface between the two refractive surfaces.
11. The image forming lens system according to claim 1 , wherein the following Conditional Expression (4) is satisfied:
60 ≤νdGF max (4)
where
νdGFmax is a largest Abbe number of Abbe numbers of positive lens elements in the front-side lens unit.
12. The image forming lens system according to claim 1 , wherein the front-side lens unit has a plurality of the positive lens elements.
13. The image forming lens system according to claim 1 , wherein the following Conditional Expression (6) is satisfied:
0.2≤ fGF/f≤ 0.8 (6),
where,
fGF is a focal length of the front-side lens unit; and
f is the longest focal length of the entire image forming lens system at a time of focusing to a furthest distance.
14. The image forming lens system according to claim 1 , wherein:
a first lens element is disposed closest to the object, and
the following Conditional Expression (7) is satisfied:
1.6≤ fL 1/ fGF≤ 5.0 (7),
where,
fL1 is a focal length of the first lens element; and
fGF is a focal length of the front-side lens unit.
15. The image forming lens system according to claim 3 , wherein the following Conditional Expression (9-3) is satisfied:
0.06≤| fG 2/ f|≤ 0.25 (9-3),
where,
fG2 is a focal length of the second lens unit; and
f is the longest focal length of the entire image forming lens system at a time of focusing to a furthest distance.
16. The image forming lens system according to claim 1 , wherein the following Conditional Expression (10) is satisfied:
3.0≤| MGG 2 B 2 ×( MGG 2 2 −1)|≤6.5 (10),
where,
MGG2B is a lateral magnification of a first rear-side lens system;
MGG2 is a lateral magnification of the second lens unit;
the lateral magnification is a lateral magnification at the time of focusing on an infinite object; and
the first rear-side lens system is a lens system comprising all of lenses positioned closer to an image side than the second lens unit.
17. The image forming lens system according to claim 1 , wherein the second lens unit includes two or less lens elements.
18. The image forming lens system according to claim 1 , wherein the second lens unit includes a negative lens element and a positive lens element.
19. The image forming lens system according to claim 1 , wherein the second lens unit comprises one negative lens element and one positive lens element.
20. The image forming lens system according to claim 1 , wherein:
the third lens unit has a camera shake-correction lens unit, and
the camera shake-correction lens unit moves in a direction vertical to an optical axis.
21. The image forming lens system according to claim 1 , wherein the third lens unit has:
an object-side sub-lens unit having a positive refractive power,
a camera shake-correction lens unit having a negative refractive power, and
an image-side sub-lens unit having a positive refractive power.
22. The image forming lens system according to claim 1 , wherein the aperture stop is disposed on the object side of the second lens unit.
23. The image forming lens system according to claim 1 , wherein the aperture stop is disposed between the first lens unit and the second lens unit.
24. The image forming lens system according to claim 1 , wherein the aperture stop is disposed between the first rear-side lens unit and the second lens unit.
25. The image forming lens system according to claim 1 , wherein the following Conditional Expression (14) is satisfied:
0.19 ≤DGF airmax/ DGF ≤1.0 (14),
where,
DGFairmax is a largest axial air space, of axial air spaces in the front-side lens unit; and
DGF is an axial thickness of the front-side lens unit.
26. The image forming lens system according to claim 1 , wherein the following Conditional Expression (1A) is satisfied:
0.01 ≤ΔGFGR max/ f ≤0.2 (1A)
where
f is the longest focal length of the entire image forming lens system at a time of focusing to a furthest distance, and
ΔGFGRmax is a largest on-axis air space of on-axis air spaces from an image-side surface in the front-side lens unit to an object-side surface in the rear-side lens unit.
27. The image forming lens system according to claim 1 , wherein the following Conditional Expression (15) is satisfied:
0.05 ≤ΔGFGR/fGF ≤0.4 (15)
where
ΔGFGR is an on-axis air space from an image-side surface in the front-side lens unit to an object-side surface in the rear-side lens unit, and
fGF is a focal length of the front-side lens unit.
28. The image forming lens system according to claim 1 , wherein the following Conditional Expression (16) is satisfied:
50≤ν dLp 1 (16),
where,
νdLp1 is an Abbe number of a positive lens element positioned closest to the object.
29. The image forming lens system according to claim 1 , wherein the front-side lens unit comprises two positive lens elements.
30. The image forming lens system according to claim 1 , wherein the first rear-side lens unit has at least two negative lenses.
31. The image forming lens system according to claim 1 , wherein the following Conditional Expression (17) is satisfied:
1.5≤| fG 1/ fG 2|≤6.5 (17),
where,
fG1 is a focal length of the first lens unit; and
fG2 is the focal length of the second lens unit.
32. The image forming lens system according to claim 1 , wherein the third lens unit includes a positive lens element and a negative lens element.
33. The image forming lens system according to claim 1 , wherein the following Conditional Expression (18) is satisfied:
0.12≤Σ dGF/fGF≤ 0.7 (18)
where
ΣdGF is a total thickness of the front-side lens unit, and
fGF is a focal length of the front-side lens unit.
34. The image forming lens system according to claim 1 , wherein the following Conditional Expression (19) is satisfied:
15 ≤νdGFn min≤57 (19)
where
νdGFnmin is a smallest Abbe number of Abbe numbers of negative lens elements in the front-side lens unit.
35. The image forming lens system according to claim 1 , wherein a negative lens element in the front-side lens unit is a resin lens.
36. The image forming lens system according to claim 1 , wherein the following Conditional Expression (21) is satisfied:
2.2 ≤|fGFn/fGF|≤ 6.5 (21)
where
fGFn is a focal length of any given negative lens element in the front-side lens unit, and
fGF is a focal length of the front-side lens unit.
37. The image forming lens system according to claim 1 , wherein a distance between the front-side lens unit and the first rear-side lens unit and a distance between the first rear-side lens unit and the second rear-side lens unit are always constant.
38. The image forming lens system according to claim 1 , wherein the front-side lens unit includes a lens element located closer to the object side than the predetermined negative lens element that satisfies following Conditional Expression (b-1):
0.025≤ DNx/φenp (b-1)
where
DNx is a thickness on an optical axis of the predetermined negative lens element, and
φenp is a maximum diameter of an entrance pupil of the image forming lens system in a state of achieving a longest focal length at a time of focusing to a furthest distance.
39. The image forming lens system according to claim 1 , wherein the first rear-side lens unit has an aspherical surface having a negative refractive power on an axis and in which an absolute value of a radius of curvature in any effective region off the axis is larger than an absolute value of a radius of curvature on the axis on a plane including an optical axis.
40. The image forming lens system according to claim 1 , wherein a lens element closest to the object side in the first lens unit is fixed in position.
41. The image forming lens system according to claim 1 , wherein a lens unit located closest to the image side is fixed in all states.
42. The image forming lens system according to claim 1 , wherein an aperture stop is fixed in position in all states.
43. The image forming lens system according to claim 1 , wherein the first lens unit is fixed in all states.
44. The image forming lens system according to claim 1 , wherein only the second lens unit moves in an optical axis direction.
45. The image forming lens system according to claim 1 , wherein the following Conditional Expression (22) is satisfied:
0.01≤|Δ Zah 1|≤20 (22)
where
Δ Zah 1=1000× N ×(Δ Zasph 1/ h 1),
h1 is a maximum height of on-axis subordinate light rays in the aspherical surface,
ΔZasph1 is a difference between the aspherical surface and a reference spherical surface that is measured in a direction horizontal to an optical axis at the maximum height, where the reference spherical surface is set such that its radius is a paraxial radius of curvature of the aspherical surface and its surface top is a surface top of the aspherical surface, and
N is a refractive index on d Line of a lens element having the aspherical surface.
46. The image forming lens system according to claim 1 , wherein the following Conditional Expression (23) is satisfied:
5≤|Δ Zah 1|/|Δ Zah 2|≤40 (23)
where
Δ Zah 1=1000× N ×(Δ Zasph 1/ h 1),
Δ Zah 2=1000× N ×(Δ Zasph 2/ h 2),
h1 is a maximum height of on-axis subordinate light rays in the aspherical surface,
h2 is a height half the maximum height,
ΔZasph1 is a difference between the aspherical surface and a reference spherical surface that is measured in a direction horizontal to an optical axis at the maximum height, where the reference spherical surface is set such that its radius is a paraxial radius of curvature of the aspherical surface and its surface top is a surface top of the aspherical surface,
ΔZasph2 is a difference between the aspherical surface and the reference spherical surface that is measured in the direction horizontal to an optical axis at a height half the maximum height, and
N is a refractive index on d Line of a lens element having the aspherical surface.
47. The image forming lens system according to claim 1 , wherein the front-side lens unit includes a lens element located closer to the object side than the predetermined negative lens element that satisfies following Conditional Expression (b):
0.02 ≤DNx/φenp (b)
where
DNx is a thickness on an optical axis of the predetermined negative lens element, and
φenp is a maximum diameter of an entrance pupil of the image forming lens system in a state of achieving a longest focal length at a time of focusing to a furthest distance.
48. The image forming lens system according to claim 1 , wherein the front-side lens unit includes a lens element located closer to the object side than a predetermined negative lens element that satisfies following Conditional Expression (a-1):
0.4≤| f/fLn| (a-1)
where
f is the longest focal length of the entire image forming lens system at a time of focusing to a furthest distance,
fLn is a focal length of the predetermined negative lens element, and
a lens element is a lens having two refractive surfaces which are an object-side surface and an image-side surface, and having no other refractive surface between the two refractive surfaces.
49. The image forming lens system according to claim 1 , wherein the front-side lens unit includes a lens located closer to the object side than a predetermined negative lens that satisfies following Conditional Expression (c):
0.007≤ DNx/LTL min (c)
where
DNx is a thickness on an optical axis of the predetermined negative lens element, and
LTLmin is a minimum total length of the image forming lens system.
50. An image pickup apparatus comprising:
an optical system; and
an image pickup element having an image plane and converting an image formed on the image plane by the optical system to an electrical signal,
wherein the optical system is the image forming lens system according to claim 1 .