Source: https://patents.google.com/patent/US20020057505A1/en
Timestamp: 2018-07-20 15:04:20
Document Index: 330914186

Matched Legal Cases: ['Application No. 9', 'Application No. 9', 'Application No. 10', 'Application No. 9', 'Application No. 9', 'Application No. 10']

US20020057505A1 - Super wide-angle lens and photographing apparatus having the same - Google Patents
US20020057505A1
US20020057505A1 US09892780 US89278001A US2002057505A1 US 20020057505 A1 US20020057505 A1 US 20020057505A1 US 09892780 US09892780 US 09892780 US 89278001 A US89278001 A US 89278001A US 2002057505 A1 US2002057505 A1 US 2002057505A1
US09892780
US6621645B2 (en )
In order to provide a large relative-aperture super wide-angle lens having the inclusive angle of 2ω=115° or more with the conventional projection method (y=f·tan θ) having the relative-aperture of about F 2.8, having compactness and high optical performance, and having small variation of aberration in relatively closed object distance, the lens includes, in order from the object, a divergent lens group Gn having negative refractive power and a convergent lens group Gp having positive refractive power, and the divergent lens group Gp includes at least one aspherical negative lens, and the aspherical lens satisfies predetermined conditional expressions.
In conventional projection method, when the image height is denoted by y, the focal length of a lens is denoted by f, and an angle formed by an object measured from the optical axis is denoted by θ, the expression y=f·tan θ is satisfied. In this method, although a proposal of a super wide-angle lens having the inclusive angle (angle of view) of 2ω=110° or more has been rare, and a proposal of a super wide-angle lens having the relative-aperture of F 3.5 or less has been very rare, lenses proposed by, for example, Japanese Patent Application No. 9-113798 and by Japanese Patent Application No. 9-113800 filed by the same assignee of the present application have been known.
Moreover, although a proposal of a super wide-angle lens having the inclusive angle of 2ω=115° or more with the conventional projection method, which satisfies y=f·tan θ, and having the relative-aperture of F 3.5 or less has been very rare, Japanese Patent Application No. 10-325923 filed by the same assignee of the present application, for example, has proposed a lens having the inclusive angle of 2ω=115° or more and the relative-aperture of F 3.5 or less.
However, a super wide-angle lens having the inclusive angle of 2ω=115° or more with the conventional projection method, which satisfies y=f·tan θ, and having the relative-aperture of about F 2.8 has not been proposed, and not been commercialized. In this situation with the present inventor's exertion and diligence, an optical system is obtained that has the inclusive angle (angle of view) of 2ω=118° or more with the conventional projection method, which is almost limit with the projection method and has not existed, and also has a large relative-aperture of F 2.8.
Problems for developing such an optical system are compactness to be able to use regularly, high optical performance, securing a peripheral quantity of light, and productivity of an aspherical surface. It is particularly important whether an aspherical lens to be used can be produced by using current mass production technique or not. In considering manufacturing method, instead of using a fine ground aspherical surface, which has not good productivity, to be able to use a glass molding method, which has high productivity, is directly connected to reducing costs, and is even advantageous to the user. In considering from this point of view, the aforementioned Japanese Patent Application No. 9-113798 or Japanese Patent Application No. 9-113800 proposed an optical system having a field of view of 2ω=105.6° and the relative-aperture of F 2.87. However, aspherical lenses proposed in these optical systems have been difficult to be manufactured by using a fine ground method or a glass molding method and, as a result, productivity has been low. The angle of view has been only about 105°, so that it has been insufficient. If the angle of view is made wider without taking measures, then the aspherical lens will become even more difficult to be manufactured.
Japanese Patent Application No. 10-325923 proposed a large relative-aperture super wide-angle lens having the angle of view of 2ω=118° and the relative-aperture of F 2.9. However, an aspherical lens located to an object side of the lens system was more difficult to be manufactured than the optical system described above, so that the productivity of the lens system was low. Moreover, the optical performance was insufficient, focusing method had a disadvantage, and the size was large.
The present invention is made in view of the aforementioned problem and has an object to provide a large relative-aperture super wide-angle lens having the inclusive angle (angle of view) of 2ω=115° or more with the conventional projection method, which satisfies y=f·tan θ, having the relative-aperture of about F 2.8, having compactness and high optical performance, and having small variation of aberration in relatively closed object distance.
In order to solve the problems described above, the present invention has, in order from the object, a divergent lens group having negative refractive power, and a convergent lens group having positive refractive power. The divergent lens system includes at least one negative aspherical lens element, and the aspherical lens satisfies the following conditional expressions (1) and (2): 0 < ( d φmax - d 0 ) / h max ( d 30 - d 0 ) / h 30 < 3 ( 1 )
where d0 denotes the thickness of the aspherical lens along the optical axis (center thickness), dφmax denotes the thickness of the aspherical lens parallel to the optical axis at the height of the maximum effective aperture on the image side surface, d30 denotes the thickness of the aspherical lens parallel to the optical axis at the height of 30% of the maximum effective aperture when the maximum effective aperture on the image side surface is assumed to be 100%, hmax denotes the maximum effective radius of the aspherical lens on the image side surface, h30 denotes the 30% of the maximum effective radius of the aspherical lens when the maximum effective aperture on the image side surface is assumed to be 100%, fasp denotes the paraxial focal length of the aspherical lens, and f0 denotes the focal length of the super wide-angle lens.
In the present invention, there are at least two aspherical surfaces in the divergent lens group, and the most object side aspherical surface preferably has a third order term satisfied with conditional expression (3) when the aspherical surface is expressed by the following aspherical expression (A): X  ( y ) = ( y 2 / r ) / [ 1 + ( 1 - κ · y 2 / r 2 ) 1 2 ] + C2 · y 2 + C3 ·  y  3 + C4 · y 4 + C6 · y 6 + C8 · y 8 + C10 · y 10 + C12 · y 12 + C14 · y 14 + C16 · y 16 ( A )
1×10−6 <|C3|<1×10−2 (3)
In the present invention, the super wide-angle lens having the inclusive angle of the lens system of 2ω=110° or more includes, in order from the object, a divergent lens group having negative refractive power, and a convergent lens group having positive refractive power. The divergent lens group includes, in order from the object, a negative meniscus lens having a convex surface facing to the object side, and a negative aspherical lens having at least one surface located to the image side with an aspherical shape that the radius of curvature becomes weak from the optical axis to the periphery. The aspherical lens satisfies the aforementioned conditional expression (1).
[0020]FIG. 1 is a drawing showing a lens configuration according to a first embodiment of the present invention.
[0023]FIG. 4 is a drawing showing a lens configuration according to a second embodiment.
Embodiments according to the present invention are explained below. In designing an objective lens including a photographing lens, it is most difficult to satisfy both an extremely wide angle of view and a large relative-aperture. It is nothing else but to correct Seidel aberrations exhaustively. Since such optical design has great difficulty, a lens having the inclusive angle (angle of view) of 2ω=118° or more with the conventional projection method, which is almost limit with the method, and also having a large relative-aperture of F 2.8 has not been proposed nor produced on a commercial basis.
Moreover, the converging (positive) lens group, having a characteristic of a master lens, has lens groups having fundamentally a positive-negative-positive power arrangement. Furthermore, focusing at a near-distant object is carried out by moving the whole converging (positive) lens group or a portion of it. It is preferable that the lens group moving for focusing has at least a positive lens group, a negative lens group, and a positive lens group. In addition, it is preferable that the converging lens group has a plurality of cemented lenses in order to set an appropriate value of Petzvar sum and to well correct spherical aberration and lateral chromatic aberration.
Here, correction of aberration in connection with aspherical surface, in particular, odd number order term is briefly explained. Generally, since an optical system is rotationally symmetrical with respect to the optical axis, an aspherical surface is expressed by addition of even number order terms of a series. However, in the present invention, correction of aberration can be effectively carried out by introducing odd number order term into the series. In considering an aspherical surface in meridional image plane, sag amount X differs in sign of image height Y while existing odd number order term, so that symmetric property seems not to be held. However, in Cartesian coordinate system (X, Y, Z) having the optical axis in the X coordinate axis, considering ρ=(Y2+Z2)½, signs coincide with each other, so that symmetric property is held. Third order aberration is produced in spherical system as well as aspherical system having even number order term of aspherical coefficient because the refractive surface is even number order term of ρ as shown below. Accordingly, if the refractive surface includes odd number order term, even number order aberration such as second order aberration, fourth order aberration, and the like, which have not existed, is produced. Furthermore, when the surface is a single surface and also an aspherical surface, spherical aberration exactly corresponds with the aspherical coefficients. Accordingly, superb aberration-correction effect never obtained by a spherical system can be obtained by introducing an aspherical coefficient of odd number order term.
X=C2·ρ2 +C4·ρ4 +C6·ρ6+ . . . (B)
X=ρ 2·1/(2r 0)+C4·ρ4 +C6·ρ6+ . . . (C)
X=ρ 2·1/(2r 0)+C3·ρ3 +C4·ρ4+ . . . (D)
For example, a second order spherical aberration can be derived by following expression: Δ   Yk ′ = 3 · ( nk ′ · uk ′ ) - 1 · [ ∑ i = 1 k   ( ni ′ - ni ) · C3i · hi 3 ] · R 2 ( E )
Moreover, although distortion shape has been a barrel shape in lower image portion and a pincushion shape in higher image portion, this aberration can be greatly improved by introducing third order term. In coma and spherical aberration, since lower order aberration can be corrected well, a circle of least confusion can be made smaller by correcting negative aberration produced by rather lower incident height caused by, for example, enlarging the relative-aperture. In the present invention, in order to take advantage of a large relative-aperture, since the greater effect can be expected by introducing an aspherical surface on the surface having a large angle of deviation α relative to the marginal ray (the ray having the largest numerical aperture emanated from an on-axis infinite object), it is desirable that an aspherical surface described above is introduced on a concave surface facing to the image.
The first term of the aspherical expression is expanded in a power series, and only aspherical terms regarding κ are shown in the following expression: x  ( y ) = 1 2  ( c 0 + 2  c 2 )  y 2 - 1 8  ( c 0 3  κ + 8  c 4 )  y 4 + 1 16  ( c 0 5  κ 2 + 16  c 6 )  y 6 + … ∵ c 0 = 1 r ( F )
where c 0 + 2  c 2 = 1 r 0 , r 0
denotes a paraxial radius of curvature, and r denotes a reference radius of curvature.
Accordingly, since each height h _
that the principal ray of off-axis rays correspondent with each image height passes through each lens surface is sufficiently separated with each other and also the width of rays correspondent with each image height is small, correction of aberrations can be carried out relatively separately with each rays correspondent with each image height by strongly controlling only high order terms.
As described above, the present invention makes it possible to correct aberrations by optimally arranging an aspherical surface taking h, h _
into consideration and by suitably controlling parameters such as ordinary even number order term as well as odd number order term, κ, and higher order terms of the aspherical coefficients.
In the aspherical surface, it is important that higher order terms and the conical coefficient κ are dominantly controlled in the portion where the maximum off-axis ray passes, and κ, third order term, and fourth order term are controlled in the portion of 30% height of the effective aperture. As described above, in correction of aberration, spherical aberration, lower coma of lower angle of view, and distortion can be corrected well in the vicinity of 30% height of the effective aperture, and distortion in the periphery of the image, lower coma, and astigmatism can be corrected well in the vicinity of the maximum effective aperture.
On the other hand, when conditional expression (1) falls below the lower limit, the curvature in the periphery of the aspherical lens becomes excessively weak. Accordingly, the variation in aberration in the peripheral portion becomes extremely large, so that it causes that optical performance becomes worse. In the end, the marginal rays cannot focus any more. When the lower limit of conditional expression (1) is set to 0.3, it is desirable that better correction can be obtained. In addition, when the lower limit of conditional expression (1) is set to 0.8 or more, it is more preferable that even better optical performance of the present invention can be expected.
In order to obtain even better optical performance of the present invention, it is desirable that in addition to the aspherical lens another aspherical surface is arranged for correcting off-axis aberrations, in particular, lower coma and spherical aberration. Furthermore, it is desirable in consideration of productivity that the aspherical lens is fabricated by the glass molding method or the compound method composed of glass and resin.
Conditional expression (2) defines a condition regarding the paraxial power of the aspherical lens. In the aspherical surface expressed by the aforementioned aspherical expression, the paraxial amount such as the focal length includes not only the paraxial radius of curvature but also second order aspherical term as shown in the first term of the mathematical expression (5). When conditional expression (2) exceeds the upper limit, the negative paraxial power of the aspherical lens becomes excessively large, so that local variation in the aspherical surface curve becomes excessively large in order to keep the shape defined by the range of conditional expression (1), and, as a result, it is undesirable that each aberration mentioned above becomes worse.
On the other hand, when conditional expression (5) falls below the lower limit, since the retrofocus ratio becomes too small, a super wide-angle lens according to the present invention produces mechanical interference with a mirror or the like, so that it may causes inconvenience that the lens cannot be applied to a lens for a single lens reflex.
[0078]FIG. 1 is a drawing showing a lens configuration of a super wide-angle lens according to a first embodiment of the present invention. The lens is composed of two lens groups, in order from an object, a divergent lens group Gn having negative refractive power and a convergent lens group Gp having positive refractive power. The divergent lens group Gn is composed of, in order from the object, a negative meniscus lens L1 having a convex surface facing to the object side, an aspherical negative meniscus lens L2 having a convex surface facing to the object side and having an aspherical surface facing to an image side, a positive meniscus lens L3 having a convex surface facing to the object side, a compound type aspherical double concave lens L4 having a compound type aspherical surface composed of glass and resin facing to the image side wherein the aspherical surface is formed on resin, a cemented positive lens composed of a negative meniscus lens L5 having a convex surface facing to the object side and a thick double convex lens L6.
Various values associated with this embodiment are listed in Table 1. In Table, the number in the left most column denotes a lens surface number counted from the object side, ri denotes the radius of curvature of the i-th lens surface Ri, di+1 denotes the distance along the optical axis between the lens surfaces Ri and Ri+1, vi denotes Abbe number of the medium between the lens surfaces Ri and Ri+1, and ni denotes the refractive index for the d-line (λ=587.56 nm) of the medium between the lens surfaces Ri and Ri+1. A star mark “★” is added to an aspherical surface, the paraxial radius of curvature is listed on the column for radius of curvature, and κ and respective aspherical coefficients are listed in the aspherical data section.
In the various values, f0 denotes the focal length, β denotes the photographing magnification, FNO denotes the f-number, and 2ω denotes the angle of view (inclusive angle). By the way, the unit of length such as the radius of curvature is mm.
2ω = 118.3°
1) 49.1686 3.2000 49.61 1.772500
2) 29.0414 10.4500 1.000000
3) 36.9310 3.1500 49.52 1.744429
★ 4) 16.5607 8.2000 1.000000 hmax = 20.79*
5) 49.1426 5.4500 64.10 1.516800
6) 109.6301 2.2000 1.000000
7) −1351.7476 2.4500 45.30 1.794997
8) 18.0000 0.1000 38.70 1.552230
★ 9) 18.5889 11.5500 1.000000
10) 84.9665 1.8000 42.72 1.834310
11) 15.6386 15.8500 33.80 1.647690
12) −36.5124 1.2000 1.000000
13) 77.0703 6.0000 48.87 1.531720
14) −180.4056 1.5500 1.000000
15) 59.6966 9.3000 48.87 1.531720
16) −26.7247 0.4500 1.000000
17) 126.8401 3.8500 52.42 1.517420
18) −17.4698 1.3000 37.35 1.834000
19) 48.0387 2.0000 1.000000
20> d20 1.000000 aperture stop
21) −772.3579 4.0000 70.24 1.487490
22) −13.7605 1.3000 49.61 1.772500
23) −17.5351 0.1000 1.000000
24) −341.9896 1.3000 45.30 1.794997
25) 19.3148 3.7000 82.52 1.497820
26) −62.8479 0.3000 1.000000
27) 69.1177 4.0000 82.52 1.497820
28) −17.6971 1.0000 46.58 1.804000
29) −42.0166 BF 1.000000
C8: −2.63440×10−10
C6: −8.58180×10−9
1-POS 2-POS 3-POS 4-POS
f0 or β 13.38000 −0.02500 −0.10000 −0.17292
D0 ∞ 509.9354 108.7109 52.3863
d20: 3.77748 3.44122 2.43480 1.45963
BF: 38.08638 38.42264 39.42906 40.40423
(Values for the conditional expressions) ( d φmax - d 0 ) / h max ( d 30 - d 0 ) / h 30 = 2.443 ( 1 )
f asp /f 0=−3.227 (2)
|C3=0.97966×10−4 (3)
FIGS. 2A-2E are graphs showing various aberrations according to the present embodiment when the lens is focused at infinity. As is apparent from the respective graphs, excellent correction is made for various aberrations. FIGS. 3A-3E are graphs showing various aberrations according to the present embodiment when the photographing magnification is −1/40. As is apparent from the respective graphs, the variation in aberration while focusing at a near-distant object is well corrected. In graphs showing various aberrations, FNO denotes the f-number, Y denotes an image height, d and g denote aberration curves for d-line and g-line, respectively. In the graphs showing astigmatism, a solid line indicates a sagittal image plane and a broken line indicates a meridional image plane. In the following embodiments, the same symbols as this embodiment are employed.
[0111]FIG. 4 is a drawing showing a lens configuration of a super wide-angle lens according to a second embodiment. The lens is composed of two lens groups, a negative and a positive lens groups, in order from an object, a divergent lens group Gn having negative refractive power and a convergent lens group Gp having positive refractive power. The divergent lens group Gn is composed of, in order from the object, a negative meniscus lens L1 having a convex surface facing to the object side, an aspherical negative meniscus lens L2 having a convex surface facing to the object side and having aspherical surfaces on both object and image sides, a negative meniscus lens L3 having a convex surface facing to the object side, a triple cemented positive lens composed of a thick double convex lens L4, a double concave lens L5, and a thick double convex lens L6, and a double convex lens L7. The converging lens group Gp is composed of, in order from the object, a positive meniscus lens L8 having a concave surface facing to the object side, a cemented positive lens composed of a double convex lens L9 and a thick double concave lens L10, an aperture stop S, a cemented positive lens composed of a thick negative meniscus lens L11 having a convex surface facing to the object side and a double convex lens L12, and a cemented positive lens composed of a double convex lens L13 and a negative meniscus lens L14 having a concave surface facing to the object side.
2ω = 118.9°
1) 80.5145 2.0000 49.45 1.772789
2) 21.2709 8.6441 1.000000
★ 3) 26.8136 2.4000 45.37 1.796681
★ 4) 12.4522 9.2092 1.000000 hmax = 17.78*
5) 36.2138 2.5000 49.45 1.772789
6) 25.4097 3.0282 1.000000
7) 38.3479 12.0010 40.76 1.581440
8) −16.9894 1.8500 49.61 1.772500
9) 18.3548 8.0000 32.17 1.672700
10) −1535.8467 0.1000 1.000000
11) 38.7424 4.0000 38.02 1.603420
12) −148.7969 d12 1.000000
13) −42.3829 2.7000 70.41 1.487490
14) −24.5665 0.1000 1.000000
15) 21.7191 6.0000 82.52 1.497820
16) −18.0871 5.0000 43.35 1.840421
17) 214.6171 d17 1.000000
18> 1.0000 1.000000 aperture stop S
19) 468.2634 8.0000 52.30 1.748099
20) 23.6125 5.5000 70.41 1.487490
21) −16.2338 0.1000 1.000000
22) 78.8775 5.4206 82.52 1.497820
23) −13.6227 1.0000 45.37 1.796681
24) −50.3950 BF 1.000000
C8: −8.58730×10−10
C12: 0.41649×10−14
f0 or β 13.39818 −0.03333 −0.10000 −0.23152
D0 ∞ 387.5292 118.8044 42.7863
d12: 6.97454 6.72518 6.69378 6.43616
d17: 3.66079 3.41143 2.53774 0.96888
BF: 38.02528 38.52400 39.42909 41.25557
(Values for the conditional expressions) ( d φmax - d 0 ) / h max ( d 30 - d 0 ) / h 30 = 1.669 ( 1 )
FIGS. 5A-5E are graphs showing various aberrations according to the second embodiment when the lens is focused at infinity. As is apparent from the respective graphs, excellent correction is made for various aberrations. FIGS. 6A-6E are graphs showing various aberrations according to the second embodiment when the photographing magnification is −1/30. As is apparent from the respective graphs, the variation in aberration while focusing at a near-distant object is well corrected.
As described above, the present invention makes it possible to provide a large relative-aperture super wide-angle lens having the inclusive angle of 2ω=118° or more with the conventional projection method (y=f·tan θ) having the relative-aperture of about F 2.8, having compactness and high optical performance, and having small variation of aberration in relatively closed object distance, and to provide a photographing apparatus equipped with the lens.
wherein the aspherical negative lens satisfies the following conditional expressions;
0 < ( d φmax - d 0 ) / h max ( d 30 - d 0 ) / h 30 < 3 ( 1 )
X  ( y ) = ( y 2 / r ) / [ 1 + ( 1 - κ · y 2 / r 2 ) 1 / 2 ] + C2 · y 2 + C3 ·  y  3 + C4 · y 4 + C6 · y 6 + C8 · y 8 + C10 · y 10 + C12 · y 12 + C14 · y 14 + C16 · y 16 ( A )
10. A super wide-angle lens with the angle of field 2ω=110° or more comprising, in order from an object;
wherein the aspherical negative lens satisfies the following conditional expression;
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