JP2004240464A - Optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact and low-cost zoom optical system consisting of a small number of lenses. <P>SOLUTION: The zoom optical system is constituted of a 1st negative lens group, a 2nd positive lens group, a 3rd negative lens group and a 4th positive lens group. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

    The present invention relates to an optical system used in various optical systems.

    Generally, in the zoom optical system, in order to reduce aberration fluctuation during zooming in addition to aberration correction in the reference state, it is desirable that aberration generated in each lens group is corrected by each lens group alone. For this purpose, each lens group is usually composed of a plurality of lenses.

    In recent years, zoom optical systems used in various optical systems have been strongly required to be reduced in size and cost. In order to achieve the miniaturization of the zoom optical system, it is only necessary to increase the refractive power of the lens unit having a zooming effect paraxially and to reduce the amount of movement of this lens unit during zooming. However, if the refractive power of the lens group is increased, the amount of generated aberration increases, and the number of lenses must be increased in order to correct the aberration and reduce the amount of generated aberration. When the number of lenses is increased as described above, it is impossible to achieve downsizing and cost reduction of the optical system. Due to such a vicious cycle, when the zoom optical system is constituted by a homogeneous lens system, there is a limit to miniaturization and cost reduction.

    Therefore, in order to further reduce the size of the zoom optical system, it is known to use a radial type gradient index lens having a refractive index distribution in the medium in the radial direction from the optical axis.

    Since the radial type gradient index lens has a refractive index distribution in the medium, the radial type gradient index lens has a greater degree of freedom for aberration correction than a homogeneous lens. In particular, since the medium also has a refractive index, it has excellent characteristics in correcting Petzval sum and chromatic aberration.

    As a conventional example using a radial type gradient index lens in the optical system, for example, the lens systems of Examples 5 and 6 of JP-A-61-231517 and Example 2 of JP-A-61-248015 are disclosed. A lens system, a lens system according to a third embodiment of JP-A-2-79013, and the like are known. However, each of these zoom optical systems is a zoom optical system having a zoom ratio of about 3 and has 9 to 13 lenses in spite of using a radial type gradient index lens, and has a large number of lenses. It is.

    The present invention provides a small and inexpensive zoom optical system having a small number of lenses.

    The optical system according to the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a third lens group having a positive refractive power. The second lens group includes at least one refractive index distribution as a lens medium in the second lens group. Further, the optical system of the present invention is an optical system that performs zooming by moving the second lens group along the optical axis.

    Since the radial type gradient index lens has a refractive power in the lens medium, the degree of freedom of aberration correction is greater than that of a homogeneous lens. In general, a zoom optical system generally includes a plurality of lenses in order to correct various aberrations by each lens group alone. If the number of lenses in each lens group is reduced in order to achieve cost reduction in such a zoom optical system, the amount of aberration generated in each lens group increases, making it difficult to obtain good imaging performance. Become. Therefore, by using a radial type gradient index lens for the zoom optical system, the lens system can be configured with a smaller number of lenses than a homogeneous lens, and a compact and low-cost zoom optical system can be realized.

    In order to realize a compact and low-cost zoom optical system, it is desirable to provide at least one radial type gradient index lens in a lens group that contributes to zooming.

    When the refractive power of the lens group that contributes to zooming is increased in order to achieve the miniaturization of the zoom optical system, it is particularly difficult to correct chromatic aberration and Petzval sum whose generation amount largely depends on the refractive power. These aberrations cannot be corrected by using an aspherical surface, and in the case of a homogeneous lens system, it must be corrected by increasing the number of lenses. In order to correct these chromatic aberrations and Petzval sum, it is desirable to include at least one radial type gradient index lens excellent in correcting these aberrations in the lens group. In particular, if a radial type gradient index lens is used for the lens group that contributes to zooming of the zoom optical system, the number of lenses will not increase even if the refractive power of this lens group is increased in order to achieve downsizing of the lens system. In addition, the Petzval sum and chromatic aberration can be corrected well. For example, in a negative-positive-negative-positive four-group zoom optical system, it is desirable to use a radial type refractive index distribution lens for the second lens group that mainly performs zooming.

    For the above reasons, the optical system of the present invention has the above-described configuration.

    Another optical system according to the present invention includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. And a zoom optical system that performs zooming by moving the second lens group along the optical axis, wherein at least one radial type gradient index lens is used.

    This zoom optical system according to the present invention can also be realized as a small and low-cost lens system.

    In the optical system according to the present invention, which is a negative / positive / positive three-unit zoom optical system, it is desirable to use at least one radial type gradient index lens for the second lens group mainly contributing to zooming.

    Normally, in the case of a homogeneous lens, if the refractive power and glass type are determined, the Petzval sum and the generation amount of chromatic aberration are determined. However, the radial type gradient index lens can control the amount of these aberrations to a desired value by controlling the parameters as described above.

    By using a radial type gradient index lens for the zoom optical system and controlling each parameter, the amount of aberrations can be set to a desired value.

When the refractive index distribution of the radial type gradient index lens medium is approximated by the square equation, it is expressed by the following equation (a).

    The primary axial chromatic aberration, that is, the chromatic aberration PAC of the d-line, the C-line, and the F-line, and the Petzval sum PTZ are represented by equations (b) and (c).

PAC = K (φ _S / V _0d + φ _m / V _1d ) (b)
PTZ = φ _S / N _0d + φ _m / N _0d ² (c)
Here, K is a constant depending on the ray height of the on-axis ray and the ray angle on the final surface, V _0d is the Abbe number at the d-line on the optical axis of the radial type gradient index lens, and V _id is the 2i-order refractive index. A value representing the dispersion corresponding to the distribution coefficient N _2i , φ _S is the refractive power of a thin wall at the d-line of the radial type gradient index lens, φ _m is the refractive power of the medium of the radial type gradient index lens, V _0d , V _id, φ _m are respectively the following formula (d), (e), it is given in (f).

V _0d = (N _0d -1) / (N _0F -N _0C ) (d)
_Vid = _Nid / ( _{NiF- NiC} ) (i = 1, 2, 3 ...) (e)
φ _m ≒ -2N _id t _G (f)
Here, t _G is the lens thickness of the radial type gradient index lens.

    As is clear from equations (b) and (c), by setting the value of the second term to which the refractive power of the medium contributes in each equation to an appropriate value, the desired chromatic aberration and Petzval sum can be obtained in a radial form. The refractive index distribution lens can be obtained by itself. For example, if the refractive power of the medium is extremely small, the second term in equations (b) and (c) becomes almost zero, and it is difficult to have the effect of correcting the chromatic aberration and Petzval sum.

    In the optical system of the present invention having the above-described configuration, it is preferable that the radial type gradient index lens satisfy the following condition (1).

(1) 0.01 <| N _1d · t _G | <1
If this condition (1) is satisfied, chromatic aberration and Petzval sum can be corrected well. If the lower limit of 0.01 to condition (1) is exceeded, the refractive power of the medium becomes weak, making it difficult to satisfactorily correct chromatic aberration and Petzval sum. When the value exceeds the upper limit of 1, chromatic aberration and Petzval sum are overcorrected.

    For better correction of chromatic aberration and Petzval sum, it is desirable that the following condition (1-1) is satisfied instead of the condition (1).

(1-1) 0.02 <| N _1d · t _G | <0.2
From equation (f), in order to increase the refractive power of the medium of the radial type gradient index lens element, the second-order dispersion coefficient N _1d is increased, that is, the difference Δn between the refractive index distribution on the optical axis and the periphery is calculated. What is necessary is just to make it large or to make a lens thickness large. However, in actually manufacturing a radial type gradient index lens material, there is a certain limit to increasing Δn. Further, for example, when the refractive index distribution material is formed by an ion exchange method or a sol-gel method, the time for providing the refractive index distribution becomes long in order to increase Δn, which causes a problem such as high cost of the material. Therefore, Δn of the radial type gradient index lens cannot be extremely increased.

In the optical system of the present invention, in order to effectively correct chromatic aberration and Petzval sum by the radial type gradient index lens, it is desirable that the lens thickness t _G satisfies the following condition (2).

However, f _W, f _T is the focal length of the entire system at each wide end and the telephoto end.

    If the condition (2) is satisfied, it is possible to provide the medium with a refractive power sufficient to correct chromatic aberration and Petzval sum without increasing Δn extremely. If the lower limit of 0.05 of the condition (2) is exceeded, chromatic aberration and Petzval sum will be insufficiently corrected. If the upper limit of 2 is exceeded, these aberrations are overcorrected, which is not preferable.

It is more preferable that the following condition (2-1) is satisfied instead of the condition (2).

It is more desirable that the following condition (2-2) be satisfied.

    Another third configuration of the present invention is an optical system composed of a plurality of lens groups, wherein at least one lens in the optical system is a refractive index distribution lens having a refractive index distribution in a medium. It is characterized in that a lens group having one element moves on the optical axis mainly for zooming, and the aperture stop moves on the optical axis together with this moving lens group. In the case where a refractive index distribution lens is used for a lens group that moves during zooming in a zoom optical system, it is desirable that the movable refractive index distribution lens and the aperture stop be moved integrally on the optical axis. With this configuration, the height of off-axis light rays entering the refractive index distribution lens becomes substantially constant irrespective of the zoom state, and it becomes possible to correct aberrations well in all states.

    If the refractive index distribution lens and the aperture stop do not move together on the optical axis, it is difficult to satisfactorily correct off-axis aberrations such as coma in all states from the wide-angle end to the telephoto end. Become.

    Further, if the refractive index distribution lens and the aperture stop are moved integrally on the optical axis, there is an advantage in terms of cost reduction in addition to an advantage in aberration correction. That is, the off-axis ray height near the aperture stop is relatively low, and the diameter of the gradient index lens can be reduced. If the lens diameter of the gradient index lens is small, the manufacturing cost of the gradient index lens element is reduced, and a low-cost optical system can be achieved. Further, even when the refractive index distribution lens is not movable, disposing the refractive index distribution lens near the aperture stop is effective for reducing the cost of the optical system.

    As described above, when the gradient index lens is disposed near the aperture stop, the present invention is not limited to the radial type gradient index lens but may be an axial type gradient index lens or an aspheric lens. Further, the refractive index distribution lens and the stop can be incorporated in the same lens frame member and can be moved on the optical axis. Further, the refractive index distribution lens and the stop may be incorporated in different lens frame members and moved on the optical axis respectively.

    Also, it is desirable that the sign (positive or negative sign) of the refractive power of the medium of the radial type gradient index lens be the same as the sign of the refractive power of the lens group using the radial type gradient index lens. This is particularly advantageous for correcting Petzval sum.

    In the radial type gradient index lens, the denominator of the second term of the equation is squared, as is clear from equation (c). Therefore, the Petzval sum generated can be reduced as compared with a homogeneous lens having the same refractive power. Therefore, it is desirable that the medium has a refractive power having the same sign as the refractive power of the lens group. In particular, when a refractive index distribution lens is used for a lens group mainly contributing to zooming, it is desirable because the optical system can be reduced in size. For example, the optical system having the above-described configuration, which includes, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a subsequent lens group. In a case where a radial type gradient index lens is used for the second lens group in an optical system in which the second lens group mainly has a zooming function, the medium preferably has a positive refractive power.

    In the case of a negative, positive, negative, positive four-group zoom optical system or a negative, positive, positive three-group zoom optical system, when the second lens group mainly has a zooming function, a lens group other than the second lens group is used as a movable group during zooming. It is preferable to correct the image plane position.

    In the case of an optical system having two or more lens units having a variable power function, if a radial type gradient index lens is used for any one of the lens units having a variable power function, the size and cost can be reduced. Can be achieved. For example, the first lens group having a positive refractive power, the second lens group having a negative refractive power, the third lens group having a positive refractive power, and the subsequent lens groups, and the second lens group and the third lens group. In the case where the lens group is a variable power optical system in which the lens group has a variable power function, any one of the second lens group and the third lens group, or both the second lens group and the third lens group If a radial type gradient index lens is used for the group, the size and cost of the optical system can be reduced.

    In the zoom optical systems having the respective configurations according to the present invention, it is preferable that at least one surface of the radial type gradient index lens used in these optical systems is flat, because flat polishing is less expensive than spherical polishing. In addition, it is more preferable that the radial type gradient index lens has a two-sided planar shape in order to achieve low cost.

    Further, in an optical system using an image pickup device such as a CCD, it is desirable to reduce an incident angle of an off-axis ray on an image plane in order to prevent a shortage of light amount in a peripheral portion of an image. In order to reduce the angle of incidence of off-axis light rays on the image plane, it is preferable that the lens closest to the image in the optical system be a positive lens or a positive cemented lens.

    Also, in order to make the optical system compact and low cost with a small number of lenses, the most image side lens of the lens system composed of a plurality of lens groups should be a positive lens, and a radial type It is desirable to adopt a configuration in which a refractive index distribution lens is arranged. In the optical system having such a configuration, when the lens group including the radial type gradient index lens moves on the optical axis, the light flux from the radial type gradient index lens is converged on the image plane by the positive lens closest to the image side. The zoom optical system can be configured with a small number of lenses.

    Also, in an optical system that requires a certain degree of back focus, in order to achieve miniaturization and cost reduction, in a lens system composed of a plurality of lens groups, the lens closest to the image as a positive lens, It is desirable to include a lens group having a configuration in which a negative lens is disposed on the object side of the positive lens and a radial type gradient index lens is disposed on the object side of the negative lens. The negative lens of this lens system mainly has the function of increasing the back focus.

    In the zoom optical system having a plurality of lens groups according to the third configuration of the present invention, it is desirable that the first lens group closest to the object be fixed during zooming. If the first lens group is fixed as described above, the strength against an external impact or pressure can be increased in the lens frame configuration. If the first lens group is movable, the movable mechanism of the lens frame may be damaged by external impact or pressure.

    Further, in a zoom optical system including a plurality of lens groups, it is desirable that the lens group closest to the image side in terms of aberration correction be fixed during zooming. The lens group closest to the image mainly has an image forming function. Therefore, if this lens group is fixed, fluctuations in aberrations during zooming can be reduced.

    In the zoom optical system of each configuration of the present invention, it is desirable to satisfy the following condition (3) in order to sufficiently and sufficiently correct chromatic aberration by the radial type gradient index lens used in the optical system.

(3) 1 / V _1d <0.15
If the condition (3) is not satisfied, chromatic aberration will be insufficiently corrected.

    It is more preferable that the following condition (3-1) is satisfied instead of the condition (3).

(3-1) −0.1 <1 / V _1d <0.1
If the value exceeds the upper limit of 0.1 to condition (3-1), chromatic aberration will be undercorrected. If the lower limit of -0.1 is exceeded, chromatic aberration will be overcorrected.

    It is more desirable that the following condition (3-2) is satisfied instead of the condition (3-1).

(3-2) −0.02 <1 / V _1d <0.02
In particular, when the optical system is used as an optical system requiring high-definition image quality, it is desirable to satisfy the following condition (3-3).

(3-3) −0.01 <1 / V _1d <0.01
The optical system of the present invention described above is used as an optical system of a silver halide camera, a video camera, a digital camera, an endoscope, an imaging device, a measuring instrument, and the like.

    In the case of manufacturing a radial type gradient index lens by, for example, an ion exchange method or a sol-gel method, it is not easy to control the refractive index distribution with high accuracy, and the refractive index distribution at the outer periphery of the lens may deviate from a designed value. The material whose refractive index distribution deviates from the design value can be used as a non-defective lens by correcting the deviation amount by processing the outer diameter. For example, a non-defective product can be obtained relatively easily by removing the outer peripheral portion of the lens material or adding a transparent member such as a resin to correct the deviation amount. Further, by providing a diaphragm, it is possible to shield the light beam so as not to pass through the outer peripheral portion.

    Further, as described above, the radial type gradient index lens can control the chromatic aberration generated in the medium to a desired value, so that a prism optical system with less chromatic aberration can be achieved by using this.

    In general, when glass is given a prism function to refract the optical axis, chromatic aberration occurs due to a difference in refractive index depending on the wavelength on the refraction surface. Therefore, if the prism optical system is configured using a radial type gradient index lens, it is possible to satisfactorily correct the chromatic aberration of the entire prism optical system by setting the chromatic aberration generated in the medium to a desired value. In this case, it is desirable to use only one radial type gradient index lens used in the prism optical system in order to achieve low cost.

    Further, as the size of various optical systems is reduced, the diameter of a lens used in the optical system also tends to be reduced. However, when the diameter of the lens is small, it becomes difficult to assemble a plurality of lenses with high accuracy. In particular, it is not easy to assemble a lens having a diameter of 10 mm or less with high accuracy. Therefore, it is desired that the number of lenses in the optical system is small, and for that purpose, it is preferable to use a gradient index lens. By using a refractive index distribution lens, it is possible to obtain an optical system having good optical performance with a smaller number of lenses than a homogeneous lens, and thus it is easy to assemble the lens. In addition, the refractive index distribution lens tends to be thicker, so that the edge thickness is relatively thicker, which makes it easier to hold the lens and assemble it with high precision.

    The refractive index distribution lens is effectively used for a lens having a diameter of 10 mm or less, and more effective for a lens having a diameter of 5 mm or less. However, in view of manufacturability, the refractive index distribution lens preferably has a lens diameter of 0.1 mm or more. If the diameter is extremely small, it becomes difficult to hold or process the lens. Therefore, more preferably, the diameter of the gradient index lens is 0.2 mm or more.

    In addition, when the diameter of the radial type gradient index lens is small, the cost for producing the material is reduced, which is also desirable from this point.

    Further, in recent years, the diameter of an image sensor has tended to decrease with the increase in the density of the image sensor such as a CCD. Therefore, it is desirable to use a gradient index lens even in an optical system using an image sensor. In particular, it is effective to use a gradient index lens in an optical system in which the size of an image pickup device such as a CCD has a screen diagonal length of 1/2 inch (image height 4 mm) or less. More desirably, it is effective to use a gradient index lens in the optical system of an optical element having an image sensor such as a CCD having a screen diagonal length of 1/3 inch (image height 3 mm) or less.

    Further, the refractive index distribution material used in the optical system of the present invention is approximated by the square equation represented by the equation (a). However, in the case of a refractive index distribution material represented by an expression other than the expression (a), it is possible to approximate the expression (a) and apply it to the optical system of the present invention.

    Further, the present invention is not limited to what is described in the claims, but may be any as long as it substantially satisfies the configuration described in the claims.

    The optical system of the present invention was able to achieve good optical performance with a small optical system having a small number of lenses by effectively arranging the radial type gradient index lenses. In particular, in a zoom optical system, a small, high-performance optical system is realized by using a radial type gradient index lens for a lens group that contributes to zooming.

    Next, an optical system according to an embodiment of the present invention will be described with reference to the drawings.

Each embodiment of the present invention is an optical system having the following data in the configuration shown in FIGS.
Example 1
f = 6.56 to 10.78 to 18.91, F number = 3.6 to 4.7 to 6.2
2ω = 60.4 ° ~ 36 ° ~ 20 °
r ₁ = ∞ d ₁ = 0.8000 n ₁ = 1.81600 ν ₁ = 46.62
r ₂ = 5.6195 d ₂ = 0.4788
r ₃ = 6.1295 d ₃ = 0.9983 n ₂ = 1.84666 ν ₂ = 23.78
r ₄ = 11.5281 d ₄ = D ₁ (variable)
r ₅ = ∞ (aperture) d ₅ = 0.5000
r ₆ = ∞ d ₆ = 5.9864 n ₃ (refractive index distribution lens)
r ₇ = ∞ d ₇ = D ₂ (variable)
r ₈ = 11.6948 d ₈ = 0.8000 n ₄ = 1.74077 ν ₄ = 27.79
r ₉ = 5.7435 d ₉ = D ₃ (variable)
_{r 10 = 15.2627 d 10 = 1.4009} n 5 = 1.88300 ν 5 = 40.76
r ₁₁ = -26.2228 d ₁₁ = 0.1993
r ₁₂ = ∞ d ₁₂ = 1.6000 n ₆ = 1.51633 ν ₆ = 64.14
r ₁₃ = ∞d ₁₃ = 1.6000 n ₇ = 1.51633 ν ₇ = 64.14
r ₁₄ = ∞ d ₁₄ = 0.4000
r ₁₅ = ∞ d ₁₅ = 0.7500 n ₈ = 1.51633 ν ₈ = 64.14
r ₁₆ = ∞ d ₁₆ = 1.1255
r ₁₇ = ∞ (image)
f 6.56 10.78 18.91
D ₁ 11.06493 5.95704 0.50000
D ₂ 5.81906 6.47619 11.96499
D ₃ 1.82166 6.33050 6.36121
Refractive index distribution lens wavelength N ₀ N ₁
d-line 1.65000 -9.2600 × 10 ^-3
C line 1.64512 -9.2557 × 10 ^-3
F line 1.66138 -9.2700 × 10 ^-3
Example 2
f = 6.68 to 10.93 to 19.39, F number = 2.4 to 3.1 to 4.2
2ω = 60 ° ~ 36 ° ~ 19.8 °
r ₁ = −361.5471 d ₁ = 1.0000 n ₁ = 1.81600 ν ₁ = 46.62
r ₂ = 7.0279 d ₂ = 0.8270
r ₃ = 7.6415 d ₃ = 2.4141 n ₂ = 1.84666 ν ₂ = 23.78
r ₄ = 12.9691 d ₄ = D ₁ (variable)
r ₅ = ∞ (aperture) d ₅ = 0.5000
r ₆ = ∞ d ₆ = 4.7683 n ₃ (refractive index distribution lens)
r ₇ = ∞ d ₇ = D ₂ (variable)
_{r 8 = 11.9747 d 8 = 0.9999} n 4 = 1.84666 ν 4 = 23.78
r ₉ = 6.5959 d ₉ = D ₃ (variable)
r ₁₀ = 21.3761 d ₁₀ = 1.8432 n ₅ = 1.88300 ν ₅ = 40.76
r ₁₁ = -21.3051 d ₁₁ = 1.0000
r ₁₂ = ∞ d ₁₂ = 1.6000 n ₆ = 1.51633 ν ₆ = 64.14
r ₁₃ = ∞d ₁₃ = 1.6000 n ₇ = 1.51633 ν ₇ = 64.14
r ₁₄ = ∞ d ₁₄ = 1.0000
r ₁₅ = ∞ d ₁₅ = 0.7500 n ₈ = 1.51633 ν ₈ = 64.14
r ₁₆ = ∞ d ₁₆ = 1.1681
r ₁₇ = ∞ (image)
f 6.68 10.93 19.39
D ₁ 14.87539 8.67516 2.00000
D ₂ 7.18816 8.25510 15.35672
D ₃ 0.95504 6.09207 5.68683
Refractive index distribution lens wavelength N ₀ N ₁ N ₂
d-line 1.75000 -9.4769 × 10 ^-3 4.7643 × 10 ^-6
C line 1.74250 -9.4684 × 10 ^-3 4.7643 × 10 ^-6
F line 1.76750 -9.4968 × 10 ^-3 4.7643 × 10 ^-6
Example 3
f = 6.58-10.05-18.18, F-number = 3.8-4.0-4.8
2ω = 59.8 ° -36.2 ° -20 °
r ₁ = 16.8604 d ₁ = 2.1134 n ₁ = 1.83481 ν ₁ = 42.72
r ₂ = -391.7314 d ₂ = D ₁ (variable)
r ₃ = 103.5216 d ₃ = 1.0000 n ₂ = 1.61800 ν ₂ = 63.33
r ₄ = 6.9508 d ₄ = 1.4921
r ₅ = −7.4105 d ₅ = 1.0000 n ₃ = 1.79216 ν ₃ = 54.68
r ₆ = -68.1757 d ₆ = D ₂ (variable)
r ₇ = ∞ (aperture) d ₇ = 1.0000
r ₈ = 87.3294 d ₈ = 5.8926 n ₄ (refractive index distribution lens)
r ₉ = ∞d ₉ = 4.0561
r ₁₀ = 12.55839 d ₁₀ = 1.0000 n ₅ = 1.84666 ν ₅ = 23.78
r ₁₁ = 8.5354 d ₁₁ = 5.1373
r ₁₂ = 13.2633 d ₁₂ = 1.21414 n ₆ = 1.83481 ν ₆ = 42.72
r ₁₃ = 136.3787 d ₁₃ = D ₃ (variable)
r ₁₄ = ∞ d ₁₄ = 1.8000 n ₇ = 1.61700 ν ₇ = 62.80
r ₁₅ = ∞ d ₁₅ = 0.2000
r ₁₆ = ∞ d ₁₆ = 0.7500 n ₈ = 1.51633 ν ₈ = 64.14
r ₁₇ = ∞ d ₁₇ = 1.1715
r ₁₈ = ∞ (image)
f 6.58 10.05 18.18
D ₁ 1.06245 2.85460 3.49323
D ₂ 10.72360 6.43554 0.50000
D ₃ 0.49996 2.33703 8.32438
Refractive index distribution lens wavelength N ₀ N ₁
d-line 1.65000 -9.2600 × 10 ^-3
C line 1.64512 -9.2557 × 10 ^-3
F line 1.66138 -9.2700 × 10 ^-3
Example 4
f = 6.12 to 10.37 to 17.41, F number = 3.1 to 3.3 to 3.4
2ω = 64 ° ~ 37.8 ° ~ 22.8 °
r ₁ = 21.5966 d ₁ = 2.4811 n ₁ = 1.84666 ν ₁ = 23.78
r ₂ = 83.9279 d ₂ = D ₁ (variable)
r ₃ = 2148.0415 d ₃ = 0.7999 n ₂ = 1.77250 ν ₂ = 49.60
r ₄ = 7.7737 d ₄ = D ₂ (variable)
r ₅ = ∞ (aperture) d ₅ = 1.0000
r ₆ = ∞d ₆ = 7.0573 n ₃ (refractive index lens)
r ₇ = ∞ d ₇ = D ₃ (variable)
r ₈ = 25.3819 d ₈ = 0.7999 n ₄ = 1.84666 ν ₄ = 23.78
r ₉ = 6.9348 d ₉ = D ₄ (variable)
r ₁₀ = 160.7405 d ₁₀ = 2.0020 n ₅ = 1.84666 ν ₅ = 23.78
r ₁₁ = -9.8318 d ₁₁ = D ₅ (variable)
r ₁₂ = ∞ d ₁₂ = 1.6000 n ₆ = 1.51633 ν ₆ = 64.14
r ₁₃ = ∞d ₁₃ = 1.6000 n ₇ = 1.51633 ν ₇ = 64.14
r ₁₄ = ∞ d ₁₄ = 1.5000
r ₁₅ = ∞ d ₁₅ = 0.7500 n ₈ = 1.51633 ν ₈ = 64.14
r ₁₆ = ∞d ₁₆ = 1.1568
r ₁₇ = ∞ (image)
f 6.12 10.37 17.41
D ₁ 1.89674 6.02579 9.83419
D ₂ 15.19674 7.32933 1.00000
D ₃ 2.27608 0.14807 0.42202
D ₄ 0.92932 3.69229 5.15328
D ₅ 0.19982 3.32183 4.12121
Refractive index distribution lens wavelength N ₀ N ₁ N ₂
d-line 1.65000 -9.2600 × 10 ^-3 1.0785 × 10 ^-5
C line 1.64512 -9.2557 × 10 ^-3 1.0780 × 10 ^-5
F line 1.66138 -9.2700 × 10 ^-3 1.0796 × 10 ^-5
g-line 1.67083 -9.2518 × 10 ^-3 1.1185 × 10 ^-5
Example 5
f = 4.75 to 8.67 to 13.94, F number = 2.7 to 3.8 to 4.8
2ω = 71 ° ~ 40.5 ° ~ 24.2 °
r ₁ = 295.4949 d ₁ = 1.6000 n ₁ = 1.84666 ν ₁ = 23.78
r ₂ = -33.3209 d ₂ = 0.2000
r ₃ = -61.1954 d ₃ = 0.8000 n ₂ = 1.61800 ν ₂ = 46.62
r ₄ = 5.4615 d ₄ = 2.0212
r ₅ = 6.3586 d ₅ = 1.6000 n ₃ = 1.84666 ν ₃ = 23.78
r ₆ = 7.8635 d ₆ = D ₁ (variable)
r ₇ = ∞ d ₇ = 6.9390 n ₄ (refractive index distribution lens)
r ₈ = ∞ d ₈ = D ₂ (variable)
r ₉ = 6.7708 d ₉ = 0.7997 n ₅ = 1.84666 ν ₅ = 23.78
r ₁₀ = 4.5573 d ₁₀ = D ₃ (variable)
r ₁₁ = 26.7807 d ₁₁ = 1.8000 n ₆ = 1.81600 ν ₆ = 46.62
r ₁₂ = -11.9170 d ₁₂ = 0.1999
r ₁₃ = ∞d ₁₃ = 1.6000 n ₇ = 1.51633 ν ₇ = 64.14
r ₁₄ = ∞ d ₁₄ = 1.6000 n ₈ = 1.51633 ν ₈ = 64.14
r ₁₅ = ∞ d ₁₅ = 0.4000
r ₁₆ = ∞ d ₁₆ = 0.7500 n ₉ = 1.51633 ν ₉ = 64.14
r ₁₇ = ∞ d ₁₇ = 1.1419
r ₁₈ = ∞ (image)
f 4.75 8.67 13.94
D ₁ 11.45422 5.39034 1.00000
D ₂ 3.98909 5.04270 11.13732
D ₃ 2.20490 7.18586 5.47117
Refractive index distribution lens wavelength N ₀ N ₁ N ₂
d-line 1.80000 -8.3994 × 10 ^-3 6.9866 × 10 ^-6
C line 1.79200 -8.3821 × 10 ^-3 6.9866 × 10 ^-6
F line 1.81867 -8.4397 × 10 ^-3 6.9866 × 10 ^-6
g-line 1.83483 -8.4356 × 10 ^-3 6.9866 × 10 ^-6
e-line 1.80630 -8.4145 × 10 ^-3 6.9866 × 10 ^-6
Example 6
f = 4.22 ~ 7.46 ~ 11.59, F number = 3.5 ~ 3.7 ~ 3.9
2ω = 59.2 ° -32.6 ° -21 °
r ₁ = -83.2538 d ₁ = 0.9563 n ₁ = 1.72916 ν ₁ = 54.68
r ₂ = 13.7980 d ₂ = D ₁ (variable)
r ₃ = ∞ (aperture) d ₃ = 1.0000
r ₄ = 8.2784 d ₄ = 6.1835 n ₂ (refractive index distribution lens)
r ₅ = 3.7725 d ₅ = 3.4709
r ₆ = 9.3241 d ₆ = 1.5000 n ₃ = 1.72916 ν ₃ = 54.68
r ₇ = -21.8979 d ₇ = D ₂ (variable)
_{r 8 = ∞ d 8 = 1.8000} n 4 = 1.61700 ν 4 = 62.80
r ₉ = ∞d ₉ = 0.2000
r ₁₀ = ∞ d ₁₀ = 0.7500 n ₅ = 1.51633 ν ₅ = 64.14
r ₁₁ = ∞ d ₁₁ = 1.2424
r ₁₂ = ∞ (image)
f 4.22 7.46 11.5
D ₁ 23.99294 7.93421 0.50000
D ₂ 1.00000 2.93580 5.39558
Refractive index distribution lens wavelength N ₀ N ₁
d-line 1.65000 -9.2600 × 10 ^-3
C line 1.64512 -9.2557 × 10 ^-3
F line 1.66138 -9.2700 × 10 ^-3
Example 7
f = 7.82 to 10.73 to 23.55, F number = 2.6 to 3.2 to 5.0
2ω = 45.8 ° -23 ° -15 °
r ₁ = -87.9283 d ₁ = 1.0110 n ₁ = 1.88300 ν ₁ = 40.76
r ₂ = 8.5547 d ₂ = 0.3932
r ₃ = 8.7336 d ₃ = 3.9684 n ₂ = 1.68893 ν ₂ = 31.08
r ₄ = 94.0338 d ₄ = D ₁ (variable)
r ₅ = ∞ (aperture) d ₅ = 1.0502
r ₆ = ∞ d ₆ = 11.8703 n ₃ (refractive index distribution lens)
r ₇ = 5.0684 d ₇ = D ₂ (variable)
r ₈ = 21.3858 d ₈ = 2.4007 n ₄ = 1.60300 ν ₄ = 65.44
r ₉ = -19.6447 d ₉ = D ₃ (variable)
r ₁₀ = ∞ d ₁₀ = 2.0200 n ₅ = 1.51633 ν ₅ = 64.14
r ₁₁ = ∞ d ₁₁ = 1.6000 n ₆ = 1.51633 ν ₆ = 64.14
r ₁₂ = ∞d ₁₂ = 1.6000
r ₁₃ = ∞d ₁₃ = 0.7500 n ₇ = 1.51633 ν ₇ = 64.14
r ₁₄ = ∞ d ₁₄ = 1.1586
r ₁₅ = ∞ (image)
f 7.82 10.78 23.55
D ₁ 20.16326 15.52315 2.07349
D ₂ 2.42907 8.51751 21.98237
D ₃ 1.61275 0.19996 0.19997
Refractive index distribution lens wavelength N ₀ N ₁ N ₂
d-line 1.58000 -6.0000 × 10 ^-3 2.0040 × 10 ^-5
C line 1.57652 -5.9775 × 10 ^-3 1.9965 × 10 ^-5
F line 1.58812 -6.0525 × 10 ^-3 2.0216 × 10 ^-5
Example 8
f = 6.55 ~ 11 ~ 19.46, F number = 3.6 ~ 4.8 ~ 6.4
2ω = 60.4 ° -35.6 ° -14.1 °
r ₁ = 40.9080 d ₁ = 0.7999 n ₁ = 1.69680 ν ₁ = 55.53
r ₂ = 5.7662 d ₂ = 1.403
r ₃ = 6.1102 d ₃ = 1.2293 n ₂ = 1.84666 ν ₂ = 23.78
r ₄ = 7.3191 d ₄ = D ₁ (variable)
r ₅ = ∞ (aperture) d ₅ = 0.5000
r ₆ = 10.7147 d ₆ = 1.2317 n ₃ = 1.77250 ν ₃ = 49.60
r ₇ = -202.6535 d ₇ = 2.7200
r ₈ = 15.4248 d ₈ = 1.6245 n ₄ = 1.88300 ν ₄ = 40.76
r ₉ = -7.0963 d ₉ = 0.1988
r ₁₀ = −6.0819 d ₁₀ = 0.8000 n ₅ = 1.84666 ν ₅ = 23.78
r ₁₁ = 59.2972 d ₁₁ = D ₂ (variable)
r ₁₂ = 15.5725 d ₁₂ = 0.8000 n ₆ = 1.54814 ν ₆ = 45.78
r ₁₃ = 5.77769 d ₁₃ = D ₃ (variable)
_{r 14 = 13.2623 d 14 = 1.9556} n 7 = 1.88300 ν 7 = 40.76
r ₁₅ = -40.0039 d ₁₅ = 0.1998
r ₁₆ = ∞ d ₁₆ = 1.6000 n ₈ = 1.51633 ν ₈ = 64.14
r ₁₇ = ∞ d ₁₇ = 1.6000 n ₉ = 1.51633 ν ₉ = 64.14
r ₁₈ = ∞ d ₁₈ = 0.4000
r ₁₉ = ∞ d ₁₉ = 0.7500 n ₁₀ = 1.51633 ν ₁₀ = 64.14
r ₂₀ = ∞ d ₂₀ = 1.1663
r ₂₁ = ∞ (image)
f 6.55 11 19.46
D ₁ 11.53674 5.96880 0.50000
D ₂ 2.09559 2.70333 7.71887
D ₃ 2.60453 7.57840 8.04678
Example 9
f = 7.52, F number = 2.9, 2ω = 59 °
r ₁ = ∞ (aperture) d ₁ = 0.5000
r ₂ = −4.2544 d ₂ = 3.3444 n ₁ (refractive index distribution lens)
r ₃ = -8.1332 d ₃ = 3.0948
r ₄ = 10.1395 d ₄ = 3.9600 n ₂ = 1.80610 ν ₂ = 40.92
r ₅ = -4.6038 d ₅ = 0.7983 n ₃ = 1.84666 ν ₃ = 23.78
r ₆ = -25.3258 d ₆ = 2.4766
r ₇ = ∞ d ₇ = 1.6000 n ₄ = 1.51633 ν ₄ = 64.14
r ₈ = ∞ d ₈ = 1.6000 n ₅ = 1.51633 ν ₅ = 64.14
r ₉ = ∞d ₉ = 0.5000
r ₁₀ = ∞ d ₁₀ = 0.7500 n ₆ = 1.48749 ν ₆ = 70.23
r ₁₁ = ∞ d ₁₁ = 1.1912
r ₁₂ = ∞ (image)
Refractive index distribution lens wavelength N ₀ N ₁
d-line 1.65000 -9.2600 × 10 ^-3
C line 1.64487 -9.2558 × 10 ^-3
F line 1.66197 -9.2699 × 10 ^-3
Example 10
r ₁ = ∞ (aperture) d ₁ = 15.0000 n ₁ (refractive index distribution lens)
r ₂ = ∞d ₂ = 0.0925
r ₃ = ∞ (image)
Refractive index distribution lens wavelength N ₀ N ₁
d line 1.67800 -9.0245 × 10 ^-3
C line 1.67265 -9.0959 × 10 ^-3
F line 1.69049 -8.8577 × 10 ^-3
Example 11
f = 4.89 to 8.63 to 20.4, F number = 3.2 to 4.1 to 6.6
2ω = 76.6 ° -44.4 ° -19.2 °
r ₁ = 17.8104 d ₁ = 2.6456 n ₁ = 1.74100 ν ₁ = 52.64
r ₂ = 6.7693 d ₂ = 2.5884
r ₃ = 330.8548 d ₃ = 0.8000 n ₂ = 1.60300 ν ₂ = 65.44
r ₄ = 8.6751 d ₄ = 0.7126
r ₅ = 8.4625 d ₅ = 1.6000 n ₃ = 1.84666 ν ₃ = 23.78
r ₆ = 16.3699 d ₆ = D ₁ (variable)
r ₇ = ∞ (aperture) d ₇ = 0.5000
r ₈ = ∞ d ₈ = 5.4448 n ₄ (refractive index distribution lens)
r ₉ = -40.2775 d ₉ = D ₂ (variable)
r ₁₀ = 7.1860 d ₁₀ = 2.8854 n ₅ = 1.78472 ν ₅ = 25.68
r ₁₁ = 4.5503 d ₁₁ = D ₃ (variable)
r ₁₂ = 29.4393 d ₁₂ = 2.0000 n ₆ = 1.69680 ν ₆ = 55.53
r ₁₃ = -12.3722 d ₁₃ = 0.2000
r ₁₄ = ∞ d ₁₄ = 1.6000 n ₇ = 1.51633 ν ₇ = 64.14
r ₁₅ = ∞ d ₁₅ = 1.6000 n ₈ = 1.51633 ν ₈ = 64.14
r ₁₆ = ∞ d ₁₆ = 0.4000
r ₁₇ = ∞ d ₁₇ = 0.7500 n ₉ = 1.51633 ν ₉ = 64.14
r ₁₈ = ∞d ₁₈ = 1.1493
r ₁₉ = ∞ (image)
f 4.89 8.63 20.4
D ₁ 17.65743 8.86991 1.00000
D ₂ 4.75469 6.19762 16.16667
D ₃ 2.00000 5.65005 9.32004
Refractive index distribution lens wavelength N ₀ N ₁ N ₂
d-line 1.70000 -6.2418 × 10 ^-3 -1.1880 × 10 ^-5
C line 1.69475 -6.2588 × 10 ^-3 -1.1912 × 10 ^-5
F line 1.71225 -6.2021 × 10 ^-3 -1.1804 × 10 ^-5
g-line 1.72241 -6.1441 × 10 ^-3 -1.1589 × 10 ^-5
Where r ₁ , r ₂ ,... Are the radii of curvature of each lens surface, d ₁ , d ₂ ,... Are the thicknesses and lens intervals of each lens, and n ₁ , n ₂ ,. refractive index, ν _1, ν _2, ··· is the Abbe number of each lens.

    Example 1 is an optical system having the configuration shown in FIG. 1, which includes, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a negative refractive power. This is a zoom optical system including a fourth lens unit having a positive refractive power. The parallel plates arranged in the fourth and subsequent groups are various filters such as a low-pass filter and an infrared cut filter and a cover glass of the image pickup device.

    In this embodiment, the first unit is fixed at the time of zooming, has an action of guiding the on-axis light beam and the off-axis light beam to the second group, and the second group is movable at the time of zooming, and mainly has a zooming action. The third unit is movable at the time of zooming and has an action of mainly correcting a shift of the image plane position due to the zooming, and the fourth unit is fixed at the time of zooming and controls the luminous flux from the third unit. It has the function of forming an image.

    As described above, Example 1 was a four-group zoom optical system of negative, positive, negative, positive, and was able to achieve a small and low-cost optical system by using a radial type gradient index lens in the optical system. In addition, by using a radial type gradient index lens for the second lens unit having a variable power function, the refracting power of the second lens unit is strengthened, and various aberrations can be satisfactorily corrected despite the miniaturization of the optical system. Is now possible. Further, by using the radial type gradient index lens, the second group can be constituted by one lens, and a low-cost optical system can be obtained.

    Further, the optical system according to the present invention can perform focusing on a short-distance object point by moving the negative lens which is the third group along the optical axis. Focusing can also be performed by moving the first lens unit along the optical axis.

    The first group mainly includes a negative lens and a positive lens in order from the object side in order to favorably correct off-axis aberrations such as chromatic aberration of magnification and distortion. In addition, by fixing the first lens unit at the time of zooming, it is possible to adopt a lens frame configuration that increases the strength against external impact and pressure.

    Further, the lens unit (the fourth unit) closest to the image side is fixed at the time of zooming, thereby making it possible to suppress the fluctuation of aberration due to zooming.

    In the optical system according to the first embodiment, the stop is arranged on the object side of the second unit, and the stop is moved integrally with the second unit during zooming, so that aberration variation during zooming is small. I made it. Therefore, since the radial type gradient index lens and the stop, which are the second group, move together, the diameter of the radial type gradient index lens can be reduced, and the cost can be reduced. The third and fourth units on the image side of the radial type gradient index lens are constituted by a negative lens (third unit) and a positive lens (fourth unit). That is, the image side of the radial type gradient index lens is composed of a negative lens and a positive lens in order from the object side, so that the optical system can be composed of a small number of lenses. In other words, the lens configuration on the image side of the first lens unit having the function of widening the angle of view is a triplet configuration of a positive lens, a negative lens, and a positive lens, so that various aberrations can be effectively corrected with a small number of lenses. In addition, since the lens closest to the image side is a positive lens, off-axis rays can be incident on the image plane almost parallel to the optical axis. Further, all the lenses other than the refractive index distribution lens are constituted by homogeneous spherical lenses, so that there is little adverse effect due to the eccentricity of the optical system (it is strong against eccentricity) and the cost can be reduced. In addition, both surfaces of the radial type gradient index lens are flattened, thereby achieving cost reduction.

    The aberration states of the first embodiment are as shown in FIGS.

    In the second embodiment, the first unit having a negative refractive power fixed at the time of zooming, the second unit having a positive refractive power movable at the time of zooming, and The zoom optical system includes a movable third lens unit having a negative refractive power and a fourth lens unit fixed at the time of zooming and having a positive refractive power. The second group includes a radial type gradient index lens. I have. That is, the second embodiment is an optical system having a four-group configuration of negative, positive, negative, positive, and can be made small and inexpensive by using a radial type gradient index lens in the optical system.

The operation of each group of the second embodiment is almost the same as that of the first embodiment, but the F-number is smaller than that of the first embodiment, and a bright optical system is provided. For this reason, the spherical aberration particularly generated in the second group tends to be large. However, the spherical aberration is favorably corrected by using a radial type gradient index lens in this group. This second group of positive refractive power has negative spherical aberration.

Then, a positive spherical aberration is generated in the medium so that the spherical aberration is favorably corrected.

    Example 3 has a configuration as shown in FIG. 3 and includes, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power. Zoom optical system.

    Of each group of this optical system, the first group has a function of guiding the on-axis and off-axis light beams to the second group while being fixed at the time of zooming, and the second and third groups are movable at the time of zooming. It has a doubling effect and has an effect of correcting a shift of an image plane position due to zooming by changing the distance between the two units.

    The third embodiment is a three-group positive / negative / positive zoom optical system, which achieves miniaturization and cost reduction by using a radial type gradient index lens in the optical system.

    The third embodiment is a zoom optical system in which a positive lens group precedes, but a third type group having a variable power function is provided with a radial type gradient index lens element to increase the refractive power of this group. Despite achieving miniaturization, various aberrations are satisfactorily corrected. The first group is composed of one positive lens, the second group is composed of two negative lenses, and the third group is composed of three lenses of a positive lens, a negative lens and a positive lens. The most object-side lens was a radial type gradient index lens. The diaphragm is disposed on the object side of the third lens unit, and the third lens unit and the diaphragm are moved integrally to reduce the diameter of the radial type gradient index lens element to reduce the cost. Further, the third lens unit is moved along the optical axis to perform focusing on a short-distance object point. Even if the positive lens closest to the object in the third lens group is movable, focusing to an object at a close distance is possible. Further, by forming the image side of the radial type gradient index lens element of the third group in order from the object side with a negative lens and a positive lens, an optical system having good performance with a small number of lenses is obtained. In addition, lenses other than the radial type gradient index lenses are all constituted by homogeneous spherical lenses, so that they are strong in eccentricity and can achieve low cost. Also, the cost is reduced by making both surfaces of the radial type gradient index lens flat.

    Example 4 is an optical system having the configuration shown in FIG. 4, and includes, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power. And a fourth optical unit having a negative refractive power and a fifth optical unit having a positive refractive power.

    In this optical system, the first unit is fixed at the time of zooming and has an action of guiding on-axis and off-axis light beams, and the second and third units are movable at the time of zooming and mainly have a zooming action. The fourth unit mainly has a function of correcting a shift of the image plane position due to zooming, and the fifth group has a function of forming an image of the light flux from the fourth group on the image plane. are doing. In this embodiment, miniaturization and cost reduction are achieved by using a radial type gradient index lens element in a positive-negative positive-negative positive five-group zoom optical system.

    The fourth embodiment is a zoom optical system that precedes the positive lens group, but uses a radial type gradient index lens for the third lens group that mainly has a variable power function, thereby increasing the refractive power of this lens group to achieve miniaturization. Thus, various aberrations are satisfactorily corrected in spite of increasing the refractive power of the third lens unit. Each group consisted of one lens.

    Further, the stop is arranged on the object side of the third lens unit, and the stop is moved integrally with the third lens unit so as to reduce aberration fluctuations during zooming. Further, since the diaphragm and the radial type gradient index lens are moved integrally, the diameter of the radial type gradient index lens can be reduced, and the cost can be reduced. Further, the fourth group on the image side of the radial type gradient index lens is composed of one negative lens, and the fifth group is composed of one positive lens, that is, the image side of the radial type gradient index lens has only a negative lens and a positive lens. , Thereby achieving miniaturization.

    In the optical system according to the fourth embodiment, the fourth lens unit is moved along the optical axis to perform focusing on an object at a short distance. It is also possible to perform focusing to a close object point by using the positive lens of the fifth group.

    In this embodiment, all the lenses except the radial type gradient index lenses are homogeneous spherical lenses, and the optical system is strong against eccentricity, so that the cost can be reduced. In addition, both surfaces of the radial type gradient index lens are flat, which can also be achieved at low cost.

    Example 5 is an optical system having a configuration shown in FIG. 5, and includes, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a negative refractive power. This is a zoom optical system including a fourth lens unit having a positive refractive power.

    In this optical system, the first unit is fixed at the time of zooming and has an action of guiding the on-axis light beam and the off-axis light beam to the second group, and the second group is movable at the time of zooming and mainly has a zooming action. The third lens unit is movable at the time of zooming, and has an action of mainly correcting an image plane position shift caused by zooming, and the fourth lens unit is fixed at the time of zooming and couples the light flux from the third lens unit. It has the function of imaging. Thus, the present invention is a four-group zoom optical system of negative, positive, negative, positive, and small size and low cost by using a radial type lens in the optical system.

    In Example 5, an optical system having a wide angle of view was obtained by increasing the number of components of the first group to three as compared with Example 1. Further, a radial type gradient index lens is used for the second group having a variable power function, so that the refractive power of the second group is strengthened to achieve the miniaturization of the optical system and to correct various aberrations well. The second group can be constituted by one lens by using a radial type gradient index lens.

    In the fifth embodiment, the first unit mainly includes, in order from the object side, a positive lens, a negative lens, and a positive lens in order to favorably correct off-axis aberrations such as chromatic aberration of magnification and distortion. . The aperture stop is virtually provided substantially at the center of the radial type gradient index lens, which is the second unit, and therefore can move integrally with the second unit to reduce fluctuations in aberrations during zooming. . Further, since the diaphragm moves integrally with the second group, the diameter of the radial type gradient index lens, which is the second group, can be reduced to reduce the cost. In the figure, S is a virtual aperture.

    In the case where a brightness stop is virtually provided in the radial type gradient index lens as described above, it is desirable that an actual stop mechanism is provided on both the object side and the image side of the refractive index distribution lens. By doing so, the light beam can be uniformly narrowed down, the brightness unevenness in the screen can be reduced, and the resolution can be improved by the narrowing down.

FIG. 13 is a diagram showing a state of a light beam when a stop mechanism is provided on both sides of the refractive index distribution lens. Figure GL refractive index distribution lens, AX is an optical axis, L ₁ is the off-axis principal ray, L ₂ is the upper subordinate ray, L ₃ is lower subordinate ray, S ₁ is the object side of the throttle mechanism, S ₂ is the image side of the diaphragm mechanism, S ₃ denotes a stop virtual.

FIG. 13 (A) shows the case of arranging the mechanism S ₁ diaphragm on the object side of the gradient index lens. In this case, the upper subordinate ray L ₂ is the upper subordinate ray L ₂ and the lower subordinate ray L ₃ is the luminous flux to be limited by the point P of the lens GL with respect to the principal ray L ₁ is asymmetric. Therefore lower subordinate ray L to become asymmetrical narrowing be squeezed from ₃ occurs when stops down the aperture mechanism S _1. Since the degree of this asymmetrical aperture stop varies depending on the angle of view, unevenness in brightness and uneven resolution occurs in the screen when the aperture is stopped down. In order to solve this, as shown in FIG. 13B, a diaphragm mechanism is provided on both the object side and the image side of the refractive index distribution lens GL, and a virtual brightness diaphragm is provided inside the lens. It is desirable to adopt such a configuration. In this case, the upper subordinate ray L ₂ is throttle mechanism S lower subordinate ray L ₃ also limited by ₂ is limited by the stop mechanism S _1. Therefore, if the two stop mechanisms S ₁ and S ₂ are stopped down, the upper subordinate beam and the lower subordinate beam are narrowed down symmetrically with respect to the principal ray L ₁ as shown in FIG. acts as a virtual stop S ₃ is squeezed in.

    For the above reasons, in the case of an optical system having a virtual stop in the lens as in the fifth embodiment, it is desirable to provide stop mechanisms on both the object side and the image side.

    Example 6 is a zoom optical system having the configuration shown in FIG. 6 and including, in order from the object side, a first unit having a negative refractive power and a second unit having a positive refractive power. The first and second units are movable at the time of zooming, and the distance between the image plane positions due to zooming is corrected by changing the distance between the two units. As described above, the sixth embodiment is a negative / positive two-unit zoom optical system, and achieves miniaturization and cost reduction by using a radial type gradient index lens in the optical system. This embodiment is a zoom optical system preceding the negative lens group, but uses a radial type gradient index lens for the second group mainly having a zooming action, and strengthens the refractive power of the second group to improve the optical system. The miniaturization was achieved and various aberrations were corrected well.

    Further, the aperture stop is arranged on the object side of the second lens unit, and is moved integrally with the second lens unit so that the fluctuation of aberration at the time of zooming can be reduced. By moving the stop integrally with the radial type gradient index lens element, the diameter of the gradient index lens element can be reduced and the cost can be reduced. The image side of the gradient index lens is constituted by one positive lens, that is, the second group is constituted by a radial type gradient index lens and a positive lens, so that the optical system is constituted by a small number of lenses. I made it. Except for the refractive index distribution lens, all are constituted by homogeneous spherical lenses, so that an optical system which is strong in eccentricity and low in cost can be obtained.

    In addition, the radial type gradient index lens element was formed into a negative lens shape to correct especially Petzval sum and chromatic aberration, and its image-side surface was made concave to extend the back focus.

    Further, the optical system of this embodiment focuses on an object at a close distance by moving the positive lens closest to the image side of the second group along the optical axis.

    The seventh embodiment has a configuration as shown in FIG. 7, and includes, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, and a third group having a positive refractive power. This is a configured three-unit zoom optical system.

    In this embodiment, the first unit is fixed at the time of zooming and has an action of guiding the on-axis light beam and the off-axis light beam to the second group, and the second group is movable at the time of zooming and mainly has a zooming action. The third lens unit mainly has an operation of correcting a shift of the image plane position caused by zooming. In this embodiment, a negative, positive, and positive three-unit zoom optical system is realized by using a radial type gradient index lens in the optical system to achieve a small and low-cost optical system.

    In this embodiment, the zoom optical system is preceded by a negative lens group. However, a radial type gradient index lens is mainly used for the second lens group having a zooming function, and the refractive power of this lens group is increased to achieve miniaturization. Nevertheless, it has made it possible to satisfactorily correct various aberrations. In addition, since the aperture stop is arranged on the object side of the refractive index distribution lens which is the second unit, and the stop and the second unit are movable integrally, aberration fluctuation at the time of zooming can be reduced. The diameter of the radial type gradient index lens can be reduced, and downsizing can be achieved. Further, the image side lens of the refractive index distribution lens, that is, the third group is constituted by one positive lens, and the entire optical system is constituted by a small number of lenses. Furthermore, except for the refractive index distribution lens, all are constituted by homogeneous spherical lenses, and the optical system is strong against eccentricity and low in cost. The cost is reduced by making one surface of the radial type gradient index lens element flat.

    The optical system of this embodiment performs focusing by moving the third lens unit along the optical axis.

    In Example 8, as shown in FIG. 8, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a positive refractive power And a fourth lens group.

    In the optical system according to this embodiment, the first unit has a function of guiding the on-axis and off-axis luminous fluxes to the second unit fixedly at the time of zooming, and the second unit is movable at the time of zooming, and has mainly a zooming operation. The third lens unit is movable at the time of zooming, and has an action of mainly correcting a shift of the image plane position caused by zooming, and the fourth lens unit forms an image of a light beam from the third lens unit at the time of zooming. Has an action. That is, the eighth embodiment is the same negative, positive, negative, positive four-group zoom optical system as in the first embodiment. However, the difference is that all lenses of the optical system are homogeneous lenses.

    In this optical system, the first unit mainly includes, in order from the object side, a negative lens and a positive lens in order to favorably correct off-axis aberrations such as chromatic aberration of magnification and distortion. Further, since the first lens unit is fixed at the time of zooming, a lens frame structure having an increased strength against external impact and pressure can be provided. In addition, since the fourth lens unit, which is the lens unit closest to the image side, is fixed at the time of zooming, it is possible to suppress the fluctuation of aberration due to zooming. Further, the aperture stop is arranged on the object side of the second lens unit and moves together with the second lens unit, thereby making it possible to reduce aberration fluctuations during zooming.

    In this embodiment, the third unit is moved along the optical axis to perform focusing on a close object. Focusing can also be performed by moving the first or fourth lens unit on the optical axis. Focusing can also be performed by moving at least one lens in the second group.

    Embodiment 9 As shown in FIG. 9, Embodiment 9 is a single-focus optical system composed of a first group having a positive refractive power and a second group having a positive refractive power in order from the object side. The first group has a radial refractive index. One positive lens of the distribution lens, and the second group includes a cemented lens in which a negative lens and a positive lens are cemented. This embodiment has high imaging performance irrespective of the number of radial type gradient index lenses and the number of positive cemented lenses. The aperture stop was provided closest to the object. By providing the stop near the radial type gradient index lens, the diameter of the gradient index lens is reduced to reduce the cost.

    Further, in this embodiment, the surface of the radial type gradient index lens is formed into a negative lens shape, and chromatic aberration and Petzval sum are corrected well. Further, the refractive index distribution lens is formed in a meniscus shape having a concave surface facing the object side so that spherical aberration can be corrected well. The refractive index distribution lens is formed in a meniscus shape having a concave surface facing the stop side so that particularly off-axis aberrations such as coma aberration can be well corrected.

Example 10 is a prism optical system including one radial type gradient index lens as shown in FIG. FIG. 10A is a diagram in which the surface r ₁ and the optical axis AX ₂ of the medium of the refractive index distribution lens are decentered with respect to the optical axis AX ₁ of the optical system. The optical system of this example is an optical system with radial type refractive index distribution lens 1 Like was eccentric shape as shown optical axis AX ₁ to diagonal 27 a light beam ° direction of the optical system surface r ₂ An image is formed in the vicinity.

In ordinary optical glass, chromatic aberration in the plane by the prism action in the first surface r ₁ for the shape as shown occurs, chromatic aberration is corrected by the radial type refractive index distribution lens in this embodiment. In this case, it is desirable to satisfy the condition (3) in order to correct the chromatic aberration. If this condition (3) is not satisfied, chromatic aberration will be undercorrected.

    The optical system of the tenth embodiment satisfies the condition (3), and the chromatic aberration is corrected as described above.

    In FIG. 10A, the first surface is decentered with respect to the optical axis of the optical system, but a similar prism optical system is formed even when only the surface or only the medium is decentered. be able to.

FIG. 10 (B) is obtained by eccentric optical axis AX ₂ of the medium with respect to the optical axis AX ₁ of the optical system. L ₁ in the figure axis principal ray incident on the optical axis AX ₁ of the optical system, L _2, L ₃ are each dependent beam. As shown in this figure, it may be achieved prism optical system by eccentric optical axis AX ₂ of the medium with respect to the optical axis of the optical system.

    The radial-type gradient index lens of FIG. 10B is obtained by extracting only the hatched portion of the radial-type gradient index lens as shown in FIG. 10C, whereby the optical system of FIG. can get.

    Further, at least one lens is an optical system that is a gradient index lens having a refractive index distribution in a medium, and one surface of the gradient index lens or the optical axis of the medium of the gradient index lens is an optical system. When the optical axis is decentered with respect to the axis, it is desirable to satisfy the condition (3) in order to correct chromatic aberration.

    In Example 11, as shown in FIG. 11, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a positive refractive power 4 is a zoom optical system including a fourth group of powers. Further, the parallel flat plate disposed on the image side of the optical system, that is, on the image side of the fourth group, is various filters such as a low-pass filter and an infrared cut filter, and a cover glass of the image sensor.

    In the optical system of this embodiment, the first unit and the second unit are movable at the time of zooming and mainly have a zooming effect, and the third unit is movable at the time of zooming and is mainly an image associated with zooming. The fourth unit has an operation of correcting the displacement of the surface position, and the fourth unit is fixed at the time of zooming, and has an operation of forming an image of a light beam from the third unit.

    As described above, the eleventh embodiment is a negative-positive-negative-positive zoom optical system, which achieves miniaturization and cost reduction by using a radial type gradient index lens in the optical system. Also, the radial type gradient index lens is used for the second group having a variable power function, and the various groups of aberrations can be satisfactorily corrected in spite of achieving the miniaturization by increasing the refractive power of this group. Further, the second group is constituted by a single lens using a radial type gradient index lens element to reduce the cost.

    The first group mainly includes, in order from the object side, a negative lens, a negative lens, and a positive lens in order to favorably correct off-axis aberrations such as chromatic aberration of magnification and distortion. The lens unit closest to the image side, that is, the fourth unit, is fixed at the time of zooming, so that aberration fluctuations due to zooming can be suppressed. The aperture stop is disposed on the object side of the second lens unit, and the second lens unit and the stop are moved together to reduce aberration fluctuations during zooming. Further, by moving the radial type gradient index lens integrally with the stop, the diameter of the radial type gradient index lens can be reduced and the cost can be reduced. The image side of the refractive index distribution lens (second group) is composed of a negative lens (third group) and a positive lens (fourth group) in order from the object side, so that a lens system is composed of a small number of lenses. . In addition, the second, third, and fourth groups on the image side of the first group as a whole have a triplet configuration of a positive lens, a negative lens, and a positive lens. So that it can be corrected. Further, it is possible to make the lens closest to the image side a positive lens so that off-axis rays can be incident on the image plane almost parallel to the optical axis. All lenses other than the radial type gradient index lens are homogeneous spherical lenses, and are strong in eccentricity and effective for cost reduction.

Embodiment 12 As shown in FIG. 12, Embodiment 12 shows a correction method when the outer peripheral portion of the radial type gradient index lens deviates from a design value. Figure AX is an optical axis in (A) of 12, GL radial type refractive index distribution lens, L ₁₁ is axial beam aperture ratio is small in the vicinity of the optical axis, L ₁₂ is the large axis of the aperture ratio away from the optical axis It is a luminous flux.

    In the refractive index distribution lens GL shown in FIG. 12A, the refractive index distribution on the outer periphery deviates from the non-defective distribution, and the on-axis rays are in the state shown in the figure. As a result, as shown in FIG. 17A, the amount of spherical aberration generated in a portion having a large aperture ratio is rapidly increased.

    FIG. 12B shows an example in which the peripheral portion of the gradient index lens is processed to correct spherical aberration. By processing this peripheral portion, the spherical aberration is corrected as shown in FIG.

    Further, as shown in FIG. 12C, the correction can be made by adding a transparent optical material T such as glass or plastic to the periphery. In this example, the spherical aberration can be corrected as shown in FIG.

    The above-described optical system of the present invention can achieve the object of the invention by the optical system described in the following items in addition to the invention described in the claims.

  (1) The optical system according to claim 1, wherein the first lens group is fixed during zooming.

  (2) The optical system according to claim 1, wherein the second lens group includes at least one refractive index distribution lens having a refractive index distribution in a medium.

  (3) The optical system according to claim 1, wherein the fourth lens group is fixed during zooming.

  (4) The optical system according to claim 1, wherein the medium includes at least one radial type gradient index lens having a refractive index distribution in a radial direction from the optical axis, and the following condition (1) is satisfied. An optical system characterized by satisfying.

(1) 0.01 <| N _1d × t _G | <1
(5) The optical system according to claim 1, wherein the medium includes at least one radial type gradient index lens having a refractive index distribution in a radial direction from the optical axis, and the following condition (2) is satisfied. An optical system characterized by satisfying.

  (6) In the optical system according to claim 2, the first lens group is fixed at the time of zooming, and includes at least one negative lens and a positive lens. Characteristic optical system.

  (7) The optical system according to claim 2, wherein the medium includes at least one refractive index distribution lens having a refractive index distribution in the medium.

  (8) The optical system according to claim 3, wherein the optical system comprises, in order from the object side, only a negative lens unit and a positive lens unit.

  (9) The optical system according to claim 3, wherein the lens unit closest to the object is fixed during zooming.

  (10) The optical system according to claim 3, wherein the at least one refractive index distribution lens is a radial type gradient index lens having a refractive index distribution in a medium from an optical axis toward a radial direction. And an optical system satisfying the following condition (1).

(1) 0.01 <| N _1d × t _G | <1
(11) The optical system according to claim 3, wherein the at least one refractive index distribution lens is a radial type gradient index lens having a refractive index distribution in a medium in a radial direction from an optical axis, An optical system characterized by satisfying the following condition (2).

  (12) An optical system composed of a plurality of lens groups, wherein at least one lens group moves on the optical axis to perform zooming, and at least one lens in the optical system has a refractive index distribution in a medium. An optical system, which is a distribution lens, wherein the refractive index distribution lens has a shape in which both end surfaces are flat.

  (13) In the optical system described in the above item (12), a lens group moving at the time of zooming includes a refractive index distribution lens, and the lens group including the refractive index distribution lens and the aperture stop are integrated. An optical system characterized in that the optical system is configured to move to a position.

  (14) The optical system according to the above (12), wherein the following condition (3) is satisfied.

(3) 1 / V _1d <0.15
(15) In the optical system described in the above item (12), at least one refractive index distribution lens is a radial type refractive index distribution lens having a refractive index distribution in a medium in a radial direction from an optical axis, An optical system characterized by satisfying the following condition (1). (1) 0.01 <| N _1d × t _G | <1
(16) In the optical system described in the above item (12), at least one of the refractive index distribution lenses is a radial type lens having a refractive index distribution in a medium in a radial direction from an optical axis to the following condition (2). An optical system characterized by satisfying the following.

  (17) A plurality of lens groups, at least one of which is a refractive index distribution lens having a refractive index distribution in a medium. A negative lens and a positive lens are arranged on the image side of the refractive index distribution lens in order from the object side. An optical system, comprising:

  (18) The optical system according to the above (17), wherein at least one lens group performs zooming by moving on the optical axis.

  (19) The optical system according to the above (18), wherein the refractive index distribution lens has a positive refractive power in a medium, and the positive lens and the negative lens are homogeneous spherical lenses. .

  (20) The optical system according to the above (18), wherein at least one surface of the gradient index lens has a planar shape.

  (21) At least one lens is a refractive index distribution lens having a refractive index distribution in a medium, and the image side of the refractive index distribution lens is composed of only one positive lens. Optical system.

  (22) The optical system according to the above (21), wherein at least one lens group performs zooming by moving on an optical axis.

  (23) An optical system including at least one refractive index distribution lens having a refractive index distribution in a medium in an optical system, and a diaphragm mechanism provided on an object side and an image side of the refractive index distribution lens. .

  (24) In the optical system described in the above item (23), at least one refractive index distribution lens is a radial type refractive index distribution lens having a refractive index distribution in a medium in a radial direction from an optical axis, and An optical system satisfying the condition (1).

(1) 0.01 <| N _1d × t _G | <1
(25) In the optical system described in the above item (23), at least one refractive index distribution lens is a radial type refractive index distribution lens having a refractive index distribution in a medium in a radial direction from an optical axis, and An optical system satisfying the condition (2).

  (26) The optical system according to the above (23), wherein the following condition (3) is satisfied.

(3) 1 / V _1d <0.15
(27) An optical system including a refractive index distribution lens having a refractive index distribution in a medium, and processing the outer peripheral portion of the refractive index distribution lens to correct the deterioration of the imaging performance due to the refractive index distribution in the outer peripheral portion.

  (28) The optical system according to the above (27), wherein an outer peripheral portion of the refractive index distribution lens is removed.

  (29) The optical system according to the above (27), wherein a transparent optical member is added to the outer periphery of the refractive index distribution lens.

  (30) An optical system including a refractive index distribution lens having a refractive index distribution in at least one medium in a lens system, wherein at least one surface of the refractive index distribution lens is eccentric.

  (31) The optical system according to the above (30), wherein the following condition (3) is satisfied.

(3) 1 / V _1d <0.15
(32) At least one lens is a gradient index lens having a distribution of refractive index in the medium, wherein the optical axis of the medium of the refractive index distribution lens is eccentric with respect to the optical axis of the optical system. Optical system.

  (33) The optical system according to the above (32), wherein the following condition (3) is satisfied.

(3) 1 / V _1d <0.15
(34) In order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, An optical system comprising a fifth group of refractive power, wherein a refractive index distribution lens having a refractive index distribution is used for at least one medium.

  (35) The optical system according to the above (34), wherein the medium includes at least one refractive index distribution lens having a refractive index distribution in the medium.

  (36) The optical system according to the above (34), wherein all the groups are constituted by three or less lenses.

  (37) The optical system according to the above (35), wherein all the groups are constituted by two or less lenses.

  (38) The method according to claim 1, 2 or 3 of the claims or the above (12), (17), (21), (23), (27), (30), (32) or (34) The optical system described in the paragraph, wherein an image sensor having an effective diagonal length of a screen of 1/2 inch or less is used.

  (39) The method according to claim 1, 2 or 3 of the claims or the above (12), (17), (21), (23), (27), (30), (32) or (34) 13. An optical system according to claim 12, further comprising an image sensor having an effective diagonal length of a screen of 1/3 inch or less.

  (40) The method according to claim 1, 2 or 3 of the claims or the above (12), (17), (21), (23), (27), (30), (32) or (34) The optical system described in the paragraph, comprising at least one refractive index distribution lens having a refractive index distribution in a medium, wherein the diameter of the refractive index distribution lens is 0.1 mm or more and 10 mm or less.

  (41) The method according to claim 1, 2 or 3 of the claims or the above (12), (17), (21), (23), (27), (30), (32) or (34) The optical system described in the paragraph, comprising one refractive index distribution lens having a refractive index distribution in a medium, wherein the diameter of the refractive index distribution lens is 0.2 mm or more and 5 mm or less.

  (42) The claim of claim 2, 2 or 3, or the above (12), (17), (21), (23), (27), (30), (32) or (34) An imaging apparatus characterized by using the optical system described in (1).

Sectional view of Example 1 of the present invention Sectional view of Embodiment 2 of the present invention Sectional view of Embodiment 3 of the present invention Sectional view of Example 4 of the present invention Sectional view of Embodiment 5 of the present invention Sectional view of Embodiment 6 of the present invention Sectional view of Embodiment 7 of the present invention Sectional view of Example 8 of the present invention Sectional view of Embodiment 9 of the present invention Sectional view of Embodiment 10 of the present invention Sectional view of Embodiment 11 of the present invention Sectional view of Example 12 of the present invention Diagram showing the state of light rays when the stop is arranged before and after the refractive index distribution lens Aberration curves at the wide-angle end according to the first embodiment of the present invention FIG. 4 is an aberration curve diagram at an intermediate focal length according to the first embodiment of the present invention. Aberration curve at the telephoto end according to the first embodiment of the present invention It is a figure showing an outline of an aberration of Example 12 of the present invention.

Claims (3)

The first lens unit has a negative refractive power, the second lens unit has a positive refractive power, the third lens group has a negative refractive power, and the fourth lens group has a positive refractive power. An optical system characterized in that: An optical system comprising, in order from the object side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power. In an optical system composed of a plurality of lens groups, the optical system includes a refractive index distribution lens having a refractive index distribution in at least one medium, and the lens group having the refractive index distribution lens is mainly a zoom lens. And an aperture stop moves on the optical axis together with the lens group.

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