Image forming optical system and electronic image pickup apparatus equipped with same
An image forming optical system includes in order from an object side to an image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and an image-side lens group having a positive refractive power. A distance between the first lens group and the second lens group changes at the time of zooming. A refractive optical element A having a positive refractive power is positioned in the first lens group. The image forming optical system satisfies the following conditional expression (1-1), conditional expression (1-2), and conditional expression (2). νd A <30 (1-1) 0.54<θgF A <0.9 (1-2) | fG 1/ fG 2|>6.4 (2).
1. An image forming optical system comprising in order from an object side to an image side:
a first lens group having a positive refractive power;
a second lens group having a negative refractive power; and
an image-side lens group having a positive refractive power,
wherein
a distance between the first lens group and the second lens group changes at the time of zooming, and
a refractive optical element A having a positive refractive power is positioned in the first lens group,
the first lens group comprises a cemented optical element D which is positioned on a most object-side,
the cemented optical element D is arranged such that the refractive optical element A is positioned between an optical element B which is positioned on the object side and an optical element C which is positioned on the image side, and
the image forming optical system satisfies the following conditional expression (1-1), conditional expression (1-2), and conditional expression (2)
νd A <30 (1-1)
0.54<θgF A <0.9 (1-2)
| fG 1 /fG 2|>6.4 (2)
where,
nd A , nC A , nF A , and ng A denote refractive indices of the refractive optical element A for a d-line, a C-line, an F-line, and a g-line respectively,
νd A denotes Abbe's number (nd A −1)/(nF A −nC A ) for the refractive optical element A,
θgF A denotes a partial dispersion ratio (ng A −nF A )/(nF A −nC A ) of the refractive optical element A,
fG1 denotes a focal length of the first lens group, and
fG2 denotes a focal length of the second lens group.
2. The image forming optical system according to claim 1 , wherein the image forming optical system satisfies the following conditional expression (5)
0.4<θ hg A <1.2 (5)
where,
θhg A denotes a partial dispersion ratio (nh A −ng A )/(nF A −nC A ) of the refractive optical element A for an h-line, and
nh A denotes a refractive index of the refractive optical element A for the h-line.
3. The image forming optical system according to claim 1 , further comprising:
an aperture stop which is positioned between the second lens group and the image-side lens group;
wherein the image-side lens group comprises in order from the object side to the image side:
a third lens group having a positive refractive power;
a fourth lens group having a positive refractive power; and
a fifth lens group having a positive refractive power,
wherein
zooming is carried out by changing distances between the adjacent lens groups such that, at a telephoto end, a distance between the first lens group and the second lens group becomes longer, a distance between the second lens group and the third lens group becomes shorter, and a distance between the third lens group and the fourth lens group becomes longer, as compared to at a wide angle end.
4. The image forming optical system according to claim 1 , further comprising:
an aperture stop which is positioned between the second lens group and the image-side lens grow;
wherein the image-side lens group comprises in order from the object side to the image side:
a third lens group having a positive refractive power;
a fourth lens group having a positive refractive power; and
a fifth lens group having a positive refractive power,
wherein
zooming is carried out by changing distances between the adjacent lens groups such that, a distance between the first lens group and the second lens group becomes longer, a distance between the second lens group and the third lens group becomes shorter, and a distance between the third lens group and the fourth lens group becomes longer, as compared to at a wide angle end to at a telephoto end, and
a distance between the fourth lens group and the fifth lens group satisfies the following conditional expression (20)
0 <TG 45 /WG 45 <5 (20)
where,
WG 45 denotes the distance between the fourth lens group and the fifth lens group at the wide angle end, and
TG 45 denotes the distance between the fourth lens group and the fifth lens group at the telephoto end.
5. The image forming optical system according to claim 1 , comprising:
the optical element B,
wherein
the image forming optical system satisfies the following conditional expression (6)
| f B /f A |>0.15 (6)
where,
f A denotes a focal length of the refractive optical element A, and
f B denotes a focal length of the optical element B.
6. The image forming optical system according to claim 1 , comprising:
the optical element B,
wherein
the image forming optical system satisfies the following conditional expression (7)
0 <θgF B −θgF BA <0.25 (7)
where,
nd B , nC B , nF B , and ng B denote refractive indices of the optical element B for a d-line, a C-line, an F-line, and a g-line,
νd B denotes Abbe's number (nd B −1)/(nF B −nC B ) for the optical element B,
θgF B denotes a partial dispersion ratio (ng B −nF B )/(nF B −nC B ) of the optical element B,
θgF BA denotes an effective partial dispersion ratio when the refractive optical element A and the optical element B are considered as one optical element, and is expressed by the following expression
θ gF BA =f BA ×ν BA ×(θ gF A ×φ A /νd A +θgF B ×φ B /νd B )
where,
f BA denotes a combined focal length of the optical element B and the refractive optical element A, and is expressed by the following expression
1 /f BA =1 /f A +1 /f B ,
ν BA denotes Abbe's number when the refractive optical element A and the optical element B are considered as one optical element, and is expressed by the following expression
ν BA =1/( f BA ×(φ A /νd A +φ B /νd B ))
where,
φ A denotes a refractive power (φ A =1/f A ) of the refractive optical element A,
φ B denotes a refractive power (φ B =1/f B ) of the optical element B, and
φ BA denotes a combined refractive power (φ BA =1/f BA ) of the optical element B and the refractive optical element A.
7. The image forming optical system according to claim 1 , wherein the image forming optical system satisfies the following conditional expression (8)
1.0 <f A /fG 1<8.0 (8)
where,
f A denotes the focal length of the refractive optical element A, and
fG1 denotes a focal length of the first lens group.
8. The image forming optical system according to claim 1 , wherein the image forming optical system satisfies the following conditional expression (9)
−25<( Ra+Rb )/( Ra−Rb )<−0.5 (9)
where,
Ra denotes a radius of curvature on the object side of the refractive optical element A, and
Rb denotes a radius of curvature on the image side of the refractive optical element A.
9. An electronic image pickup apparatus comprising:
an image forming optical system; and
an image pickup element,
wherein
the image forming optical system is the image forming optical system according to claim 1 , and
the image forming optical system satisfies the following conditional expression (3-3)
0<( Zb (3.3 a )− Za (3.3 a ))/( Zb (2.5 a )−( Za (2.5 a ))<0.990 (3-3)
where,
fw denotes a focal length of the image forming optical system, at a wide angle end,
ft denotes a focal length of the image forming optical system, at a telephoto end,
IH denotes the maximum image height on the image pickup element,
Za(h) denotes an optical axial distance between an apex of an object-side surface on an optical axis, of the refractive optical element A and a position at a height h on the object side of the refractive optical element A,
Zb(h) denotes an optical axial distance between the apex of the object-side surface on the optical axis, of the refractive optical element and a position at a height h on the image side of the refractive optical element A,
a denotes a value defined by the following expression (3-1)
a ={( IH ) 2 ×log 10 ( ft/fw )}/ fw (3-1).
10. The image forming optical system according to claim 1 , wherein the image forming optical system satisfies the following conditional expression (9′)
−25<( Ra+Rb )/( Ra−Rb )<−2 (9′)
where,
Ra denotes a radius of curvature on the object side of the refractive optical element A, and
Rb denotes a radius of curvature on the image side of the refractive optical element A.
11. An electronic image pickup apparatus comprising:
an image forming optical system; and
an image pickup element,
wherein
the image forming optical system is an image forming optical system according to claim 1 , and satisfies the following conditional expression (3-2)
0<( Zb (3.3 a )− Za (3.3 a ))/( Zb (2.5 a )−( Za (2.5 a ))<0.895 (3-2)
where,
fw denotes a focal length of the image forming optical system, at a wide angle end,
ft denotes a focal length of the image forming optical system, at a telephoto end,
IH denotes the maximum image height on the image pickup element,
Za(h) denotes an optical axial distance between an apex of an object-side surface on an optical axis, of the refractive optical element A and a position at a height h on the object side of the refractive optical element A,
Zb(h) denotes an optical axial distance between the apex of the object-side surface on the optical axis, of the refractive optical element A and a position at a height h on the image side of the refractive optical element A,
a denotes a value defined by the following expression (3-1)
a ={( IH ) 2 ×log 10 ( ft/fw )}/ fw (3-1).
12. An electronic image pickup apparatus comprising:
an image forming optical system; and
an image pickup element,
wherein
the image forming optical system comprises in order from an object side to an image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and an image-side lens group having a positive refractive power, and a distance between the first lens group and the second lens group changes at the time of zooming, and
a refractive optical element A having a positive refractive power is positioned in the first lens group,
the first lens group comprises a cemented optical element D which is positioned on a most object-side,
the cemented optical element D is arranged such that the refractive optical element A is positioned between an optical element B which is positioned on the object side and an optical element C which is positioned on the image side, and
the refractive optical element A satisfies the following conditional expression (3-2)
0<( Zb (3.3 a )− Za (3.3 a ))/( Zb (2.5 a )−( Za (2.5 a ))<0.895 (3-2)
where,
fw denotes a focal length of the image forming optical system, at a wide angle end,
ft denotes a focal length of the image forming optical system, at a telephoto end,
IH denotes the maximum image height on the image pickup element,
Za(h) denotes an optical axial distance between an apex of an object-side surface on an optical axis, of the refractive optical element A and a position at a height h on the object side of the refractive optical element A,
Zb(h) denotes an optical axial distance between the apex of the object-side surface on the optical axis, of the refractive optical element and a position at a height h on the image side of the refractive optical element A,
a denotes a value defined by the following expression (3-1)
a ={( IH ) 2 ×log 10 ( ft/fw )}/ fw (3-1).
13. The electronic image pickup apparatus according to claim 12 , wherein the electronic image pickup apparatus satisfies the following conditional expression (1-1), conditional expression (1-2), and conditional expression (2).
νd A <30 (1-1)
0.54<θ gF A <0.9 (1-2)
| fG 1 /fG 2|>6.4 (2)
where,
nd A , nC A , nF A , and ng A denote refractive indices of the refractive optical element A for a d-line, a C-line, an F-line, and a g-line respectively,
νd A denotes Abbe's number (nd A −1)/(nF A −nC A ) of the refractive optical element A,
θgF A denotes a partial dispersion ratio (ng A −nF A )/(nF A −nC A ) of the refractive optical element A,
fG1 denotes a focal length of the first lens group, and
fG2 denotes a focal length of the second lens group.
14. The electronic image pickup apparatus according to claim 12 , comprising:
the refractive optical element A; and
the optical element B,
wherein
the refractive optical element A and the optical element B satisfy the following conditional expression (1-1), conditional expression (1-2), and conditional expression (4-3)
νd A <30 (1-1)
0.54<θgF A <0.9 (1-2)
0.05<( Tnglw (0.7)/ Tbasw (0.7))/( Tngl (0)/ Tbas (0))<0.75 (4-3)
where,
nd A , nC A , nF A , and ng A denote refractive indices of the refractive optical element A for a d-line, a C-line, an F-line, and a g-line respectively,
νd A denotes Abbe's number (nd A −1)/(nF A −nC A ) for the refractive optical element A,
θgF A denotes a partial dispersion ratio (ng A −nF A )/(nF A −nC A ) of the refractive optical element A,
Tngl(0) denotes a central thickness on an axis of the refractive optical element A,
Tnglw(0.7) denotes a length of a light ray having a height 70% of the maximum light ray height on the image pickup element at the wide angle end, passing through the refractive optical element A,
Tbas(0) denotes a central thickness on an axis of the optical element B, and
Tbasw(0.7) denotes a length of a light ray having a height 70% of the maximum light ray height on the image pickup element at the wide angle end, passing through the optical element B.
15. The electronic image pickup apparatus according to claim 12 , wherein the electronic image pickup apparatus satisfies one of the following conditional expression (10-1a), conditional expression (10-1b), conditional expression (10-1c), conditional expression (10-2a), and conditional expression (10-2b)
0.3 <Tngl (0)/ Tbas (0)<10 (10-1a)
0.15 <Tnglt (0.7)/ Tbast (0.7)<3.0 (10-1b)
0.1 <Tnglt (0.9)/ Tbast (0.9)<2.0 (10-1c)
0.1<( Tnglt (0.7)/ Tbast (0.7))/( Tngl (0)/ Tbas (0))<0.85 (10-2a)
0.05<( Tnglt (0.9)/ Tbast (0.9))/( Tngl (0)/ Tbas (0))<0.75 (10-2b)
where,
Tngl(0) denotes the central thickness on the axis of the refractive optical element A,
Tnglt(0.7) denotes a length of a light ray having a height 70% of the maximum light ray height on the image pickup element at the telephoto end, passing through the refractive optical element A,
Tnglt (0.9) denotes a length of a light ray having a height 90% of the maximum light ray height on the image pickup element at the telephoto end, passing through the refractive optical element A,
Tbas(0) denotes the central thickness on the axis of the optical element B,
Tbast(0.7) denotes a length of a light ray having a height 70% of the maximum light ray height on the image pickup element at the telephoto end, passing through the optical element B, and
Tbast(0.9) denotes a length of a light ray having a height 90% of the maximum light ray height on the image pickup element at the telephoto end, passing through the optical element B.
16. The electronic image pickup apparatus according to claim 12 , wherein the electronic image pickup apparatus satisfies one of the following conditional expression (11a) and conditional expression (11b)
0.5<( Tnglw (0.7)/( Tngl (0))<0.95 (11a)
0.3<( Tnglw (0.9)/( Tngle (0))<0.9 (11b)
where,
Tngl(0) denotes the central thickness on axis of the refractive optical element A,
Tnglw(0.7) denotes the length of the light ray having a height 70% of the maximum light ray height on the image pickup element at the wide angle end, passing through the refractive optical element A, and
Tnglw(0.9) denotes a length of a light ray having a height 90% of the maximum light ray height on the image pickup element at the wide angle end, passing through the refractive optical element A.
17. The electronic image pickup apparatus according to claim 12 , wherein the electronic image pickup apparatus satisfies one of the following conditional expression (12a) and conditional expression (12b)
0.5<( Tnglt (0.7)/( Tngl (0))<0.95 (12a)
0.3<( Tnglt (0.9)/( Tngl (0))<0.9 (12b)
where,
Tngl(0) denotes the central thickness on the axis of the refractive optical element A,
Tnglt(0.7) denotes the length of the light ray having a height 70% of the maximum light ray height on the image pickup element at the telephoto end, passing through the refractive optical element A, and
Tnglt(0.9) denotes the length of the light ray having a height 90% of the maximum light ray height on the image pickup element at the telephoto end, passing through the refractive optical element A.
18. The electronic image pickup apparatus according to claim 12 , wherein the electronic image pickup apparatus satisfies one of the following conditional expression (13-1a), conditional expression (13-1b), conditional expression (13-1c), and conditional expression (13-2)
0.3 <Tngl (0)/ Tbas (0)<10 (13-1a)
0.15 <Tnglw (0.7)/ Tbasw (0.7)<2.0 (13-1b)
0 <Tnglw (0.9)/ Tbasw (0.9)<0.9 (13-1c)
0<( Tnglw (0.9)/ Tbasw (0.9))/( Tngl (0)/ Tbas (0))<0.5 (13-2)
where,
Tngl(0) denotes the central thickness on the axis of the refractive optical element A,
Tnglw(0.7) denotes the length of the light ray having a height 70% of the maximum light ray height on the image pickup element at the wide angle end, passing through the refractive optical element A,
Tnglw (0.9) denotes the length of the light ray having a height 90% of the maximum light ray height on the image pickup element at the wide angle end, passing through the refractive optical element A,
Tbas(0) denotes the central thickness on the axis of the optical element B,
Tbasw(0.7) denotes the length of the light ray having a height 70% of the maximum light ray height on the image pickup element at the wide angle end, passing through the optical element B, and
Tbasw(0.9) denotes a length of a light ray having a height 90% of the maximum light ray height on the image pickup element at the telephoto end, passing through the optical element B.
19. The electronic image pickup apparatus according to claim 12 , wherein
the electronic image pickup apparatus satisfies the following conditional expression (4-1), conditional expression (4-2), and conditional expression (2)
νd A <30 (4-1)
0.54<θgF A <0.9 (4-2)
| fG 1 /fG 2|>6.4 (2)
where,
nd A , nC A , nF A , and ng A denote refractive indices of the refractive optical element A for a d-line, a C-line, an F-line, and a g-line respectively,
νd A denotes Abbe's number (nd A −1)/(nF A −nC A ) of the refractive optical element A,
θgF A denotes a partial dispersion ratio (ng A −nF A )/(nF A −nC A ) of the refractive optical element A,
fG1 denotes a focal length of the first lens group, and
fG2 denotes a focal length of the second lens group.
20. The electronic image pickup apparatus according to claim 12 , wherein the electronic image pickup apparatus satisfies one of the following conditional expression (10-1a′), conditional expression (10-1b′), conditional expression (10-1c′), conditional expression (10-2a′), and conditional expression (10-2b′)
0.3 <Tngl (0)/ Tbas (0)<3 (10-1a′)
0.2 <Tnglt (0.7)/ Tbast (0.7)<2.0 (10-1b′)
0.1 <Tnglt (0.9)/ Tbast (0.9)<1.4 (10-1c′)
0.2<( Tnglt (0.7)/ Tbast (0.7))/( Tngl (0)/ Tbas (0))<0.85 (10-2a′)
0.10<( Tnglt (0.9)/ Tbast (0.9))/( Tngl (0)/ Tbas (0))<0.75 (10-2b′)
where,
Tngl(0) denotes the central thickness on the axis of the refractive optical element A,
Tnglt(0.7) denotes a length of a light ray having a height 70% of the maximum light ray height on the image pickup element at the telephoto end, passing through the refractive optical element A,
Tnglt (0.9) denotes a length of a light ray having a height 90% of the maximum light ray height on the image pickup element at the telephoto end, passing through the refractive optical element A,
Tbas(0) denotes the central thickness on the axis of the optical element B,
Tbast(0.7) denotes a length of a light ray having a height 70% of the maximum light ray height on the image pickup element at the telephoto end, passing through the optical element B, and
Tbast(0.9) denotes a length of a light ray having a height 90% of the maximum light ray height on the image pickup element at the telephoto end, passing through the optical element B.
21. The electronic image pickup apparatus according to claim 12 , wherein the electronic image pickup apparatus satisfies one of the following conditional expression (11a) and conditional expression (11b′)
0.5<( Tnglw (0.7)/( Tngl (0))<0.95 (11a)
0.3<( Tnglw (0.9)/( Tngle (0))<0.85 (11b′)
where,
Tngl(0) denotes the central thickness on the axis of the refractive optical element A,
Tnglw(0.7) denotes the length of the light ray having a height 70% of the maximum light ray height on the image pickup element at the wide angle end, passing through the refractive optical element A, and
Tnglw(0.9) denotes a length of a light ray having a height 90% of the maximum light ray height on the image pickup element at the wide angle end, passing through the refractive optical element A.
22. The electronic image pickup apparatus according to claim 12 , wherein the electronic image pickup apparatus satisfies one of the following conditional expression (13-1a′), conditional expression (13-1b′), conditional expression (13-1c′), and conditional expression (13-2)
0.3 <Tngl (0)/ Tbas (0)<2.5 (13-1a′)
0.15 <Tnglw (0.7)/ Tbasw (0.7)<1.4 (13-1b′)
0 <Tnglw (0.9)/ Tbasw (0.9)<0.7 (13-1c′)
0<( Tnglw (0.9)/ Tbasw (0.9))/( Tngl (0)/ Tbas (0))<0.5 (13-2)
where,
Tngl(0) denotes the central thickness on the axis of the refractive optical element A,
Tnglw(0.7) denotes the length of the light ray having a height 70% of the maximum light ray height on the image pickup element at the wide angle end, passing through the refractive optical element A,
Tnglw (0.9) denotes the length of the light ray having a height 90% of the maximum light ray height on the image pickup element at the wide angle end, passing through the refractive optical element A,
Tbas(0) denotes the central thickness on the axis of the optical element B,
Tbasw(0.7) denotes the length of the light ray having a height 70% of the maximum light ray height on the image pickup element at the wide angle end, passing through the optical element B, and
Tbasw(0.9) denotes a length of a light ray having a height 90% of the maximum light ray height on the image pickup element at the telephoto end, passing through the optical element B.
23. An electronic image pickup apparatus comprising:
an image forming optical system; and
an image pickup element,
wherein
the image forming optical system comprises in order from an object side to an image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and an image-side lens group having a positive refractive power, and a distance between the first lens group and the second lens group changes at the time of zooming, and
the first lens group comprises a cemented optical element D which is positioned on a most object-side, and
the cemented optical element D is arranged such that, a refractive optical element A having a positive refractive power is positioned between an optical element B which is positioned on the object side and an optical element C which is positioned on the image side, and
the electronic image pickup apparatus satisfies the following conditional expression (4-1), conditional expression (4-2), and conditional expression (4-3)
νd A <30 (4-1)
0.54<θgF A <0.9 (4-2)
0.387<( Tnglw (0.7)/ Tbasw (0.7))/( Tngl (0)/ Tbas (0))<0.525 (4-3)
where,
νd A denotes Abbe's number (nd A −1)/(nF A −nC A ) for the refractive optical element A,
θgF A denotes a partial dispersion ratio (ng A −nF A )/(nF A −nC A ) of the refractive optical element A,
nd A , nC A , nF A , and ng A denote refractive indices of the refractive optical element A for a d-line, a C-line, an F-line, and a g-line respectively,
Tngl(0) denotes a central thickness on an axis of the refractive optical element A,
Tnglw(0.7) denotes a length of a light ray having a height 70% of the maximum light ray height on the image pickup element at the wide angle end, passing through the refractive optical element A,
Tbas(0) denotes a central thickness on an axis of the optical element B, and
Tbasw(0.7) denotes a length of a light ray having a height 70% of the maximum light ray height on the image pickup element at the wide angle end, passing through the optical element B.
24. The electronic image pickup apparatus according to claim 18 , wherein the electronic image pickup apparatus satisfies the following conditional expression (2)
| fG 1 /fG 2|>6.4 (2)
where,
fG1 denotes a focal length of the first lens group, and
fG2 denotes a focal length of the second lens group.
25. The electronic image pickup apparatus according to claim 23 , wherein the electronic image pickup apparatus satisfies the following conditional expression (3-2)
0<( Zb (3.3 a )− Za (3.3 a ))/( Zb (2.5 a )−( Za (2.5 a ))<0.895 (3-2)
where,
fw denotes a focal length of the image forming optical system, at a wide angle end,
ft denotes a focal length of the image forming optical system, at a telephoto end,
IH denotes the maximum image height on the image pickup element,
Za(h) denotes an optical axial distance between an apex of an object-side surface on an optical axis, of the refractive optical element A and a position at a height h on the object side of the refractive optical element A,
Zb(h) denotes an optical axial distance between the apex of the object-side surface on the optical axis, of the refractive optical element and a position at a height h on the image side of the refractive optical element A,
a denotes a value defined by the following expression (3-1)
a ={( IH ) 2 ×log 10 ( ft/fw )}/ fw (3-1).