JPH1068879A - Aberration variable optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to continuously change spherical aberrations from a negative value to a positive value across a sharp image quality state by specifying a relation of the focal length between a master lens group and a converter lens group, thereby providing the optical system having a large angle of view. SOLUTION: The master lens group GM comprises a first partial lens group L1 consisting of a biconvex lens and a positive meniscus lens, a second partial lens group L2 consisting of a biconcave lens, an aperture-stop S and a third partial lens group L3 consisting of a combined negative lens of a negative meniscus lens and a position meniscus lens and a biconvex lens. The converter lens group GC comprises a positive meniscus lens LP and a negative meniscus lens LN. The optical system is so formed as to satisfy the conditions expressed by -1<fM/fC<0 when the focal length of the master lens group GM in an afocal state is defined as fM and the focal length of the converter lens group GC in a state of the lens position that the rate of occurrence of the spherical aberration at the afocal state is smallest is defined as fC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable aberration optical system, and more particularly, to a variable soft focus lens capable of obtaining a bright soft focus image having a relatively large angle of view and a function of favorably correcting blurring. The present invention relates to a variable bokeh optical system.

[0002]

2. Description of the Related Art Hitherto, an optical system capable of obtaining an effect of soft focus (soft tone description) has been known for a long time. In particular, an optical system capable of continuously changing the effect of soft focus, that is, a variable soft focus lens, has become the mainstream of soft focus lenses in recent years. For example, Japanese Patent Application Laid-Open No. 52-76921 discloses that a tester type or a triplet type having a relatively small angle of view is used for a master portion, and a negative meniscus lens is added to the rear of the master portion. An optical system that continuously changes spherical aberration by changing an interval is disclosed.

Japanese Patent Application Laid-Open No. Sho 53-109626 discloses that the diameter of a master portion is increased by using a Gaussian type lens, and a negative meniscus lens component is added to the rear of the master portion. An optical system that continuously changes the spherical aberration by changing the optical system is disclosed. Further, although the purpose is different from that of obtaining the effect of the soft focus, an optical system for changing the depiction of the out-of-focus portion mainly by continuously generating spherical aberration is disclosed in Japanese Patent Application Laid-Open No. 1-259314. I have. The optical system disclosed in this publication has an effect similar to soft focus.

[0004]

Problems to be Solved by the Invention
The variable soft focus lens disclosed in Japanese Patent Application Laid-open No. 1 and JP-A-53-109626 has a position at which a so-called sharp image is obtained (that is, a normal mode lens position state), and a predetermined variable interval is changed. This has the effect of continuously generating spherical aberration. However, the angle of view (2ω) is 28 °
The symmetry of coma required for obtaining a soft focus image and a defocus image which are small and beautiful was not good. Further, only one of negative spherical aberration and positive spherical aberration can be generated from the position where sharp image quality is obtained. If the spherical aberration of the opposite sign is forcibly generated, the symmetry of the coma aberration is further deteriorated, and not only a beautiful soft focus image or a defocus image cannot be obtained, but also the lens component eventually becomes There was a possibility of mechanical interference, which was difficult to achieve.

In Japanese Patent Application Laid-Open No. 52-76921, a converter lens group having a positive refractive power is provided behind a master lens group, and the spherical aberration is reduced by changing the air gap in the converter lens group. A changing optical system is disclosed. However, if the power (refractive power) of the converter lens group is made positive by using a Tessar type or triplet type for the master lens group,
With similar focal lengths, the overall length cannot be made more compact.

Further, in the optical system disclosed in Japanese Patent Application Laid-Open No. 1-259314, a variable interval for changing spherical aberration is provided closest to the object. As a result, it was not possible to obtain the coma aberration symmetry required to obtain a beautiful soft focus image or defocus image. Further, it was not possible to obtain a spherical aberration amount large enough to obtain a beautiful soft focus image. The present invention has been made in view of the above-described problem, and has a sufficiently large angle of view, and can continuously change spherical aberration from a negative value to a positive value with a sharp image quality state interposed therebetween. It is an object to provide an aberration-variable optical system.

[0007]

In order to solve the above problems, according to the present invention, in order from the object side, a master lens group G _M having a positive refractive power and a converter lens group G having a negative refractive power are provided. _C , the master lens group G _M includes, in order from the object side, a first partial lens group L ₁ having a positive refractive power, a second partial lens group L ₂ having a negative refractive power, and a third lens subunit L ₃ having a refractive power, said converter lens group G _C, in order from the object side, a lens component L _P having a positive refractive power, a lens component L having a negative refractive power _N, and the positive lens component L
_The space formed between _P and the negative lens component L _N has a concave surface facing the aperture stop, and the axial air gap D between the positive lens component L _P and the negative lens component L _N is changed. A variable aberration optical system mainly for changing spherical aberration, wherein the master lens group G _M in an infinity in-focus state is provided.
Of the focal length and f _M, the focal length of said converter lens group G _C generation amount and the spherical aberration in the infinity in-focus state in the smallest lens position state was _{f C, -1 <f M /} f Provided is a variable aberration optical system that satisfies the condition of _C <0.

According to a preferred aspect of the present invention, the focal length of the negative lens component L _N is f _N, and the converter lens group G in a lens position in an infinity in-focus state and a state in which the amount of spherical aberration is minimized. _{Assuming that} the focal length of _C is f _C , the condition 0 <f _N / f _C <1 is satisfied. Further, when the Abbe number of the negative lens the negative lens in the component L _N and [nu _N, the Abbe number of the positive lens of the positive lens in the component L _P was _{ν P, -10 <ν N -ν} P <30 It is preferable to satisfy the following condition.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the basic structure of the present invention will be described. In the present invention, by using a relatively large angle of view and a relatively large lens type capable of ensuring diameter (e.g., an optical system represented by a so-called habit Bruno coater type and Gaussian type) of the master lens group G _M, Various aberrations including chromatic aberration are sufficiently corrected. Then, over a telephoto ratio by the converter lens group G _C, while compact, has sufficient back focus and the lens group moving for lens movement or defocus image control for the variable soft focus.

The "defocus image control" changes aberrations (especially spherical aberrations) to such an extent that the resolution and contrast of the object to be photographed on the image plane do not change so much. It has the effect of changing the descriptive properties (especially blurring due to front blur and rear blur). At this time, depending on how the aberration is changed,
It is possible to select between a clear change in front blur and a clear change in rear blur.

On the other hand, in the "soft focus", aberrations (particularly, spherical aberration) are largely changed to lower the contrast of the entire screen mainly corresponding to each frequency component. As a result, soft focus has an effect of creating a state in which flare fogging called so-called soft tone depiction has occurred. Therefore, in the soft focus, the contrast mainly corresponding to each frequency component on the image plane of the subject to be photographed substantially changes.

In the present invention, the master lens group G _M
And the converter lens group G _C , the variable air gap D for mainly changing the spherical aberration
From the pupil (or aperture stop). Thus, since the injection oblique rays and incidence oblique rays for the positive lens component L _P and the negative lens component L _N leaves more from the optical axis deflection angle with respect to the positive lens component L _P and the negative lens component L _N is increased, the upper and lower beams A relatively close deviation angle can be realized. Therefore, a flare with good symmetry is generated up to the peripheral portion of the screen, and a good point image can be obtained.

In particular, in the case of a soft focus lens having a large angle of view or a variable bokeh optical system such as the optical system of the present invention, the occurrence of a flare with good symmetry depends on the amount of spherical aberration generated. It is one of the equally important factors. Further, in the present invention is a space i.e. the air lens is formed between the positive lens component L _P and a negative lens component L _N is a concave surface facing against the aperture stop structure. This is to minimize the occurrence of field curvature and asymmetrical component of coma aberration when changing the on-axis air gap D to change mainly spherical aberration, and to include higher-order aberrations due to a small amount of movement of the lens group. This is for generating spherical aberration.

Hereinafter, the conditional expressions of the present invention will be described. In the present invention, the following conditional expression (1) is satisfied. _{-1 <f M / f C <} 0 (1) where, f _M: the focal length of the master lens group G _M in focus at infinity f _C: and the generation amount of the spherical aberration in the infinity in-focus state is most Focal length of converter lens group G _C with few lens positions

Conditional expression (1) represents the focal length f _M of the master lens group G _{M and} the focal length f _C of the converter lens group G _C.
An appropriate range is specified for the ratio. If the lower limit of conditional expression (1), if the focal length f _M of the master lens group G _M is constant, the converter lens group G _C
Power is significantly increased. As a result, in order to have the same focal length, it is necessary to increase the distance HH 'between the object-side principal point and the image-side principal point, so that the converter lens group G _C becomes large. In addition, as a result, the back focus becomes extremely short, so that it cannot be used for a single-lens reflex camera or the like. It should be noted that the lower limit of conditional expression (1) is-
By setting the value to 0.5, and more preferably to -0.4, the size of the optical system can be further reduced.

On the other hand, exceeding the upper limit of conditional expression (1) means that conditional expression (1) takes a positive value, that is, converter lens group G _C becomes a lens group having a positive refractive power. . As described above, in the present invention, a large angle of view and a large aperture can be obtained, a sufficient amount of spherical aberration can be obtained in both the negative direction and the positive direction, and a high image quality position (variable aberrations) can be obtained. In order to realize an optical system having a lens position in which sharp images can be obtained with less occurrence, the converter lens group G _C is composed of a lens group having a negative refractive power, thereby ensuring a small and sufficient back focus. In addition, various aberrations are satisfactorily corrected. When the value exceeds the upper limit of conditional expression (1), the required structure of the present invention is greatly deviated.
The power arrangement of the telephoto type cannot be secured. As a result, miniaturization becomes difficult, and the diameter of the rear ball also increases, which is not preferable. It should be noted that the upper limit of conditional expression (1) is-
By setting the value to 0.01, and more preferably to -0.12, the effects of the present invention can be exhibited more favorably.

In the present invention, it is desirable to satisfy the following conditional expression (2). _{0 <f N / f C <} 1 (2) where, f _N: focal length of the negative lens component L _N

[0018] Condition (2) defines an appropriate range for the ratio of the focal length f _C of the focal length f _N a converter lens group G _C of the negative lens component L _N. If the power of the converter lens group G _C is constant near the lower limit value of the conditional expression (2), the power of the negative lens component L _N becomes too strong, and in the position where sharp image quality is to be obtained, that is, in the normal mode. It becomes difficult to satisfactorily correct various aberrations. Even if good correction of various aberrations becomes possible by measures such as increasing the number of constituent lenses, sensitivity to eccentricity becomes extremely high, and manufacturing becomes difficult.

Furthermore, the lower limit value of the conditional expression (2) is that the conditional expression (2) takes a negative value, i.e., either one of the negative lens component L _N and converter lens group G _C is It has a positive refractive power. In that case, as described above, since the required configuration and method for exhibiting the effects of the present invention are not satisfied, a large angle of view and a large diameter can be achieved, and sufficient in both the negative direction and the positive direction can be achieved. An optical system that can obtain a spherical aberration amount and has a position of high image quality cannot be realized. By setting the lower limit of conditional expression (2) to 0.05, and more preferably 0.1, the effects of the present invention can be exhibited more favorably.

On the other hand, when the value exceeds the upper limit of conditional expression (2),
If the power of the converter lens group G _C is constant, the power of the negative lens component L _N becomes too weak, and it is not possible to obtain a sufficient amount of change in spherical aberration. If the amount of movement of the lens group is significantly increased and the amount of change in spherical aberration is sufficiently obtained, the change in the overall length of the optical system increases, and consequently the back focus becomes significantly shorter in the variable soft focus mode. It is not preferable because a new position is created. Further, in a vari-soft focus mode in which spherical aberration having a sign opposite to that of the position where the back focus is shortened, the lens component L _P and the lens component L _N cause mechanical interference,
As a result, a sufficient amount of change in spherical aberration cannot be obtained. By setting the upper limit of conditional expression (2) to 0.6, more preferably 0.4, it is possible to obtain a sufficient amount of change in spherical aberration.

In the present invention, it is desirable that the following conditional expression (3) is satisfied. −10 <ν _N −ν _P <30 (3) where, ν _N : Abbe number of the negative lens in the negative lens component L _N ν _P : Abbe number of the positive lens in the positive lens component L _P

[0022] Condition (3) defines an appropriate range of difference between the negative lens component L _N Abbe number [nu _P of the positive lens of the negative lens Abbe number [nu _N and a positive lens in the component L _P of in I have. The converter lens group G _C is the master lens group G _M
Is a lens group having a negative refractive power independent of. Therefore, considering the chromatic aberration of the entire optical system, it is desirable that the achromatic have been made in the converter lens group G _C. That is, it is basically desirable that the negative lens is made of a low-dispersion optical material and the positive lens is made of a high-dispersion optical material, similarly to the achromatism of a general negative lens group. For the optical system of the present invention, changing the air distance D between the positive lens component L _P and a negative lens component L _N. Therefore, if an excessively large dispersion difference is set between the two lens components, the chromatic aberration fluctuates. Therefore, it is desirable to provide an appropriate dispersion difference between the two lens components.

If the lower limit of conditional expression (3) is not reached, that is, if the dispersion of the negative lens is significantly larger than that of the positive lens, the combination will be the opposite of the achromatic state of a general negative lens group. Variations in chromatic aberration increase, and satisfactory optical performance cannot be obtained. In the case of the optical system of the present invention, the configuration of the master lens group G _M has a sufficient degree of freedom for correcting chromatic aberration. For this reason, it is also possible to use a combination in which the glass material is used in the opposite way to the achromatization of a general negative lens group, that is, a configuration in which the negative lens has a slightly larger dispersion than the positive lens (high dispersion configuration). It has become. By setting the lower limit of conditional expression (3) to -7, and more preferably to -5, better achromatism can be achieved. Furthermore, the lower limit of conditional expression (3) is set to -2.
When set to 5, the effect of the present invention can be more sufficiently exhibited.

Conversely, if the upper limit of conditional expression (3) is exceeded, that is, if the dispersion of the positive lens is significantly larger than that of the negative lens, the lens components L _P and L _N
Chromatic aberration fluctuates with a change in the air gap D between the two. The upper limit of conditional expression (3) is set to 25.
By setting the value to 15 more preferably, more excellent achromatism becomes possible. Further, when the upper limit value of conditional expression (3) is set to 10, the effects of the present invention can be more sufficiently exhibited.

In the present invention, it is desirable that the following conditional expression (4) is satisfied. -1 <(rb -ra) / ( rb + ra) <0 (4) where, ra: the positive lens component L _P in most positioned on the image side of the positive lens on the image side surface of the curvature radius rb: negative lens Radius of curvature of the object-side surface of the negative lens closest to the object side in the component L _N

[0026] Condition (4), for the inverse of the shape factor of an air lens formed between the positive lens component L _P and a negative lens component L _N (shape factor) defines an appropriate range. If the lower limit of conditional expression (4) is not reached, the shape of the air lens changes from a plano-convex shape with the convex surface facing the image side to a biconvex shape. In this case, changing the air gap D is not preferable because various aberrations other than the spherical aberration, particularly the curvature of field and asymmetrical coma aberration are remarkably generated. Here, the lower limit value of conditional expression (4) is set to -0.5, more preferably -0.5.
By setting the value to 0.2, it becomes possible to further effectively suppress the occurrence of various aberrations other than the spherical aberration, particularly, the curvature of field and asymmetric coma.

Conversely, when the value approaches the upper limit of conditional expression (4), the shape of the air lens becomes a meniscus shape with a convex surface having a remarkably large curvature directed to the image side. As a result, the deflection angle of the exit light beam and the incident light beam with respect to each surface becomes extremely large, and higher-order aberrations increase, and the performance in the position where sharp image quality, which is a feature of the present invention, that is, the normal mode is particularly deteriorated. Tend to. In addition, the eccentricity, the tolerance of the lens interval and the tolerance of the lens thickness become extremely strict, and the production becomes difficult. The upper limit of conditional expression (4) is set to -0.005.
By setting the value to -0.01, more preferably, the effect of the present invention can be more sufficiently exhibited.

In the present invention, it is desirable to satisfy the following conditional expression (5). −0.25 <n _N −n _P <0.35 (5) where, n _N : the refractive index of the negative lens in the negative lens component L _{N with} respect to the d-line n _P : the positive lens in the positive lens component L _P Refractive index for d-line

[0029] Conditional expression (5) is suitable for the difference between the refractive index n _P at the d-line of the positive lens of the refractive index n _N and a positive lens in the component L _P for the negative lens at the d-line in the negative lens component L _N Stipulates the appropriate range. When falling below a lower limit value of conditional expression (5), the refractive index of the negative lens component _LN becomes extremely small.
As a result, various higher-order aberrations increase remarkably, and the performance in a position where sharp image quality, which is a feature of the present invention, that is, a normal mode tends to be particularly deteriorated. Here, the lower limit value of conditional expression (5) is-
By setting the value to 0.2, and more preferably to -0.15, it is possible to promote the occurrence of appropriate spherical aberration and to suppress the occurrence of various aberrations, especially the curvature of field and asymmetric coma. .

[0030] Conversely, if the upper limit of the condition (5), the refractive index of the positive lens component L _P is significantly reduced. As a result, it is difficult to set the Petzval sum to an appropriate value, and the field curvature increases, which is not preferable. When the upper limit value of conditional expression (5) is set to 0.25, more preferably 0.2, the effects of the present invention can be more sufficiently exerted.

In the present invention, it is desirable that the following conditional expression (6) is satisfied. -10 <(rd + rc) / (rd -rc) <1 (6) where, rc: radius of curvature rd of the object-side surface of the positive lens component L _P: curvature of the image side surface of the positive lens component L _P radius

Conditional expression (6) indicates that the converter lens group G _C
It defines an appropriate range of the shape factor of the positive lens component L _P in. If the lower limit of the condition (6), the shape of the positive lens component L _P becomes significant meniscus shape.
As a result, the position in which sharp image quality, which is a feature of the present invention, that is, the performance in the normal mode tends to be particularly deteriorated due to the influence of higher-order aberrations, which is not preferable. When the lower limit of conditional expression (6) is set to −5, the effects of the present invention can be more sufficiently exerted. Conversely, if the upper limit of conditional expression (6), the shape of the positive lens component L _P becomes meniscus shape having a convex surface facing the object side. In this case, changing the air gap D is not preferable because various aberrations other than the spherical aberration, particularly the curvature of field and asymmetrical coma aberration are remarkably generated.

In the present invention, it is desirable that the following conditional expression (7) is satisfied. -1 <(rf + re) / (rf -re) <10 (7) where, re: the negative lens component L _N of the object-side surface of the curvature radius rf: curvature of the image side surface of the negative lens component L _N radius

Conditional expression (7) indicates that the converter lens group G _C
An appropriate range is defined for the shape factor of the middle negative lens component _LN . If the lower limit value of conditional expression (7) is not reached, the shape of the negative lens component L _N becomes a meniscus lens shape with the concave surface facing the image side exceeding the plano-concave shape with the concave surface facing the image side,
The shape of the air lens deviates significantly from the meniscus shape.
For this reason, changing the air interval D is not preferable because various aberrations other than the spherical aberration, particularly the curvature of field and asymmetrical coma aberration are remarkably generated. When the lower limit of conditional expression (7) is set to 0, the effects of the present invention can be more sufficiently exerted.

On the contrary, when the value exceeds the upper limit value of the conditional expression (7), the shape of the negative lens component _LN becomes a remarkable meniscus shape. As a result, the position in which sharp image quality, which is a feature of the present invention, that is, the performance in the normal mode tends to be particularly deteriorated due to the influence of higher-order aberrations, which is not preferable. Note that the upper limit of conditional expression (7) is set to 5
If the value is more preferably set to 2 or 1.5, the effect of the present invention can be more sufficiently exhibited.

[0036] In the present invention, in order to obtain good spherical aberration and coma aberration corresponding to large diameter, first portion Reference group L ₁ in the master lens group G _M has two positive lenses It is desirable. Also, in order to set the Petzval sum appropriately and perform sufficient achromatization,
The third lens subunit L ₃ having a positive refractive power, it is desirable to have a cemented lens and a positive lens consisting of a negative lens and a positive lens. Furthermore, for cost reduction and compactness, it is desirable to configure a positive lens component L _P and the negative lens component L _N in the converter lens group G _C by one lens, respectively.

[0037]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Aberration variable optical system according to each embodiment of the present invention includes in order from the object side, a master lens group G _M having a positive refractive power, a converter lens group G _C having a negative refractive power. And the master lens group G
_M is, in order from the object side, a first partial lens unit L ₁ having a positive refractive power and a second partial lens unit L having a negative refractive power
A _2, and a third lens subunit L ₃ having a positive refractive power. Further, the converter lens group G _C has in order from the object side, a lens component L _P having a positive refractive power and a lens component L _N having a negative refractive power.

[First Embodiment] FIG. 1 is a diagram showing a configuration and a movement locus of a variable aberration optical system according to a first embodiment of the present invention. In the aberration adjustable optical system of FIG. 1, the master lens group G _M, in order from the object side, a first lens subunit L _1, which is a positive meniscus lens having a convex surface directed toward the biconvex lens and the object side, a biconcave lens 2 partial lens unit L _2, the aperture stop S, the third lens subunit and a cemented negative lens and a biconvex lens with a positive meniscus lens having a concave surface facing the negative meniscus lens and the object side with a concave surface facing the object side L It consists of _three . Further, the converter lens group G _C, in order from the object side, is composed of a positive meniscus lens L _P having a concave surface facing the object side, a negative meniscus lens L _N having a concave surface on the object side (aperture stop S side) ing.

[0039] In the first embodiment, as shown in FIG. 1, the axis of reference to the normal mode generation amount of the spherical aberration is smallest sharp image quality can be obtained, a positive meniscus lens L _P and a negative meniscus lens L _N The soft focus mode (1) can be realized by moving the negative meniscus lens _LN so that the upper air interval D increases. Further, by moving the negative meniscus lens _LN so that the on-axis air gap D decreases, the soft focus mode (2) can be realized. Since the back focus is varied in accordance with the movement of the negative meniscus lens L _N, by integrally moving the master lens group G _M and a positive meniscus lens L _P, and corrects the variation of the back focus. In the first embodiment, focusing on a short-distance object is performed by integrally extending the entire optical system toward the object side. With this focusing method, macro photography up to 1/4 magnification is possible.

Table 1 below summarizes the data values of the first embodiment of the present invention. In Table (1), f is the focal length,
FNO represents the F number, 2ω represents the angle of view, Bf represents the back focus, and D0 represents the distance along the optical axis between the object and the surface closest to the object. Furthermore, the surface number indicates the order of the lens surface from the object side along the direction in which the light rays travel,
The refractive index and Abbe number are each d-line (λ = 587.6).
nm).

[0041]

Table 1 f = 105 FNO = 2.83 2ω = 35.72 ° Surface number Curvature radius Surface spacing Abbe number Refractive index 1 185.3082 4.0000 60.64 1.603110 2 -163.2324 0.1000 3 33.0757 7.0000 82.52 1.497820 4 84.3311 2.3000 5 -282.0428 1.8000 45.87 1.548139 6 39.4465 6.6000 7 ∞ 6.5000 (Aperture stop S) 8 -29.4505 1.8000 36.98 1.612930 9 -223.1023 7.5000 53.75 1.693500 10 -37.4314 0.1000 11 392.7974 4.5000 50.84 1.658440 12 -76.2736 6.2824 13 -247.6209 5.0000 37.90 1.723421 14 -52.9649 (d14 = variable ) 15 -40.5667 2.0000 36.98 1.612930 16 -1871.6154 (Bf) (Variable interval for soft focus and focusing) f & β 105.00000 94.00000 112.00000 -0.03333 -0.10000 D0 ∞ ∞ ∞ 3244.5250 1141.0400 d14 4.20977 8.14357 2.19293 4.20977 4.20977 Bf 69.4679672.762.762 β -0.25000 -0.03333 -0.10000 -0.03333 -0.10000 D0 509.9955 2900.8090 1020.8086 3454.4867 1214.4859 d14 4.20977 8.14357 8.14357 2.19293 2.19293 Bf 95 .76148 57.89554 64.16221 82.18461 89.65128 (Conditional value) (1) f _M / f _C = −0.2952 (2) f _N / f _C = 0.2286 (3) ν _N −ν _P = −0.92 ( 4) (rb -ra) / ( rb + ra) = - 0.1326 (5) n n -n P = -0.1105 (6) (rd + rc) / (rd -rc) = - 1.544 (7 ) (Rf + re) / (rf-re) = 1.044

FIGS. 2 to 4 show various aberration diagrams of the first embodiment. That is, FIG. 2 is a diagram of various aberrations in a normal mode in which an infinity in-focus state is obtained and the amount of spherical aberration is the smallest. FIG. 3 is a diagram of various aberrations in the soft focus mode (1) in which the subject is focused on infinity and the back blur (image of the background out-of-focus portion) is favorable. Furthermore, FIG. 4 is a diagram of various aberrations in the soft focus mode (2) in which the infinity is in focus and the front blur (image of the out-of-focus portion of the foreground) is good. In each aberration diagram, FNO represents the F number, A represents the half angle of view, and d represents the d-line (λ
= 587.6 nm) and g is the g-line (λ = 435.8 n).
m). In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane.

Referring to FIG. 2, in the normal mode,
It can be seen that various aberrations are satisfactorily corrected over the entire large angle of view, similarly to a general photographic lens. Referring to FIG. 3, in the soft focus mode (1), negative spherical aberration and off-axis spherical aberration (a symmetric flare component of coma aberration) occur greatly, and other aberrations, particularly off-axis aberrations, occur. It can be seen that the fluctuation of the amount is very small. The amount of aberration can be continuously controlled between the normal mode and the soft focus mode (1), and the image is formed by moving the lens from the normal mode to the soft focus mode (1). It becomes possible to change the defocusing effect (defocus image control) to make only the post-blur good, without deteriorating the performance of the surface much.

Further, referring to FIG. 4, in the soft focus mode (2), a positive spherical aberration and an off-axis spherical aberration (a symmetric flare component of coma aberration) largely occur, and other aberrations, particularly, It can be seen that the variation of off-axis aberration is very small. The amount of aberration can be continuously controlled between the normal mode and the soft focus mode (2), and the image is formed by moving the lens in the direction from the normal mode to the soft focus mode (2). It is possible to change the defocusing effect (defocus image control) to make only the front defocusing favorable, without deteriorating the performance of the surface much.

[0045] In the first embodiment, by integrally moving the master lens group G _M and a positive meniscus lens L _P, and corrects the variation of the back focus.
However, the negative lens component L for varying the spherical aberration
Depending on the amount of movement of _N , the fluctuation of the back focus can be corrected by various other methods. For example, by moving only the master lens group G _M, or by moving only the positive meniscus lens L _P, it is also possible to correct the variation of the back focus. Further, a group of compensators for correcting the fluctuation of the back focus can be separately provided. In the first embodiment, focusing on a short-distance object is performed by integrally extending the entire optical system toward the object side.
However, focusing on a close object can be achieved in various other ways. For example, by moving only the master lens group G _M , or by moving (floating) the master lens group G _M and the converter lens group G _C independently of each other,
Focusing on a short-distance object can also be performed.

[Second Embodiment] FIG. 5 is a diagram showing a configuration and a moving locus of a variable aberration optical system according to a second embodiment of the present invention. In the aberration adjustable optical system of FIG. 5, the master lens group G _M, in order from the object side, a first lens subunit L _1, which is a positive meniscus lens having a convex surface directed toward the biconvex lens and the object side, a convex surface on the object side a second lens subunit L ₂ consisting of a negative meniscus lens, an aperture stop S,
And a third lens subunit L ₃ Metropolitan consisting cemented negative lens and a biconvex lens of a biconcave lens and a biconvex lens. Further, the converter lens group G _C, in order from the object side, and a convex lens L _P, a concave surface facing the object side (aperture stop S side) and a biconcave lens L _N.

[0047] In the second embodiment, as shown in FIG. 5, with reference to the normal mode generation amount of the spherical aberration is smallest sharp image quality can be obtained, an axial air with a double-convex lens L _P and a biconcave lens L _N By moving the negative meniscus lens L _N so that the interval D increases, the soft focus mode (1) can be realized. Further, by moving the biconcave lens _LN so that the on-axis air gap D decreases, the soft focus mode (2) can be realized. Since the back focus changes with movement of the biconcave lens _LN , the master lens group G _M
By moving integrally with the convex lens L _P,
Back focus fluctuation is corrected. In the second embodiment, the master lens group GM is _replaced with the first partial lens group L.
A _first and second lens subunit L ₂ consisting of the front group, is divided into a rear group consisting of the third partial lens group L _3, near by moving (is floating) and the front and rear groups independently of each other Focusing on a distance object. With this focusing method, macro photography up to 1/2 times is possible.

Table 2 below summarizes data values of the second embodiment of the present invention. In Table (2), f is the focal length,
FNO represents the F number, 2ω represents the angle of view, Bf represents the back focus, and D0 represents the distance along the optical axis between the object and the surface closest to the object. Furthermore, the surface number indicates the order of the lens surface from the object side along the direction in which the light rays travel,
The refractive index and Abbe number are each d-line (λ = 587.6).
nm).

[0049]

[Table 2] f = 85 FNO = 2.85 2ω = 43.5 ° Surface number Curvature radius Surface spacing Abbe number Refractive index 1 55.6538 5.0000 48.04 1.716999 2 -2603.3146 0.1000 3 25.1841 3.4000 53.75 1.693500 4 38.3374 1.6000 5 92.2896 1.7000 36.98 1.612930 6 22.1322 (d6 = variable) 7 ∞ 4.0000 (aperture stop S) 8 -29.3026 1.7000 32.17 1.672700 9 196.5217 12.5000 53.89 1.713000 10 -39.9515 0.1000 11 334.0512 3.5000 55.60 1.696800 12 -73.6850 (d12 = variable) 13 2514.2791 7.0000 33.75 1.648310 14- 49.2645 (d14 = variable) 15 -45.2184 2.0000 40.90 1.796310 16 1264.3990 (Bf) (variable interval in soft focus and focusing) f & β 85.02000 73.00000 90.00000 -0.03333 -0.10000 D0 ∞ ∞ ∞ 2604.1136 902.5494 d6 5.51671 5.51671 5.51671 6.06841 7.18198 d12 1.960 1.96096 1.96096 3.80796 7.53598 d14 2.63421 7.07075 1.15230 2.63421 2.63421 Bf 55.73839 39.93660 62.24573 55.73839 55.73839 β -0.30000 -0.50000 -0.10000 -0.50000 -0.10000 -0.50000 D0 333.2842 2 17.3791 781.9516 192.1951 952.1982 227.6557 d6 10.60870 14.17700 7.45963 15.69403 7.08942 13.67642 d12 19.00804 30.95410 8.46553 36.03287 7.22613 29.27826 d14 2.63421 2.63421 7.07075 7.07075 1.15230 1.15230 Bf 55.73840 55.73839 39.93660 39.93661 62.24572 62.24574 ( Condition corresponding _{values) (1) f M / f} C = -0. 2958 (2) f _N / f _C = 0.2288 (3) ν _N −ν _P = 7.15 (4) (rb−ra) / (rb + ra) = − 0.0428 (5) n _N− n _P = 0.148 (6) (rd + rc) / (rd-rc) =-0.9616 (7) (rf + re) / (rf-re) = 0.9309

FIGS. 6 to 8 show various aberration diagrams of the second embodiment. FIG. 6 is a diagram illustrating various aberrations in the normal mode in which the spherical aberration is least generated in the infinity in-focus state. FIG. 7 is a diagram illustrating various aberrations in the soft focus mode (1) in which the infinity is in focus and the back blur (the image of the background out-of-focus portion) is favorable. FIG. 8 is a diagram of various aberrations in the soft focus mode (2) in which the infinity is in focus and the front blur (the image of the out-of-focus portion of the foreground) is favorable. In each aberration diagram, FNO represents the F number, A represents the half angle of view, and d represents the d-line (λ
= 587.6 nm) and g is the g-line (λ = 435.8 n).
m). In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane.

Referring to FIG. 6, in the normal mode,
It can be seen that various aberrations are satisfactorily corrected over the entire large angle of view, similarly to a general photographic lens. Referring to FIG. 7, in the soft focus mode (1), a negative spherical aberration and an off-axis spherical aberration (a flare component having symmetry of coma aberration) are largely generated, and other aberrations, particularly off-axis aberrations, are generated. It can be seen that the fluctuation of the amount is very small. The amount of aberration can be continuously controlled between the normal mode and the soft focus mode (1), and the image is formed by moving the lens from the normal mode to the soft focus mode (1). It becomes possible to change the defocusing effect (defocus image control) to make only the post-blur good, without deteriorating the performance of the surface much.

Further, referring to FIG. 8, in the soft focus mode (2), positive spherical aberration and off-axis spherical aberration (a symmetric flare component of coma aberration) are largely generated, and other aberrations, especially, It can be seen that the variation of off-axis aberration is very small. The amount of aberration can be continuously controlled between the normal mode and the soft focus mode (2), and the image is formed by moving the lens in the direction from the normal mode to the soft focus mode (2). It is possible to change the defocusing effect (defocus image control) to make only the front defocusing favorable, without deteriorating the performance of the surface much.

[0053] In the second embodiment, by integrally moving the master lens group G _M and a positive meniscus lens L _P, and it corrects the variation of the back focus.
However, the negative lens component L for varying the spherical aberration
Depending on the amount of movement of _N , the fluctuation of the back focus can be corrected by various other methods. For example, by moving only the master lens group G _M, or by moving only the positive meniscus lens L _P, it is also possible to correct the variation of the back focus. Further, a group of compensators for correcting the fluctuation of the back focus can be separately provided. In the second embodiment, is performed focusing on a close object by dividing the master lens group G _M in the front and rear groups, moves the front and rear groups independently of each other. However, focusing on a close object can be achieved in various other ways. For example, by feeding the entire optical system to integrally object side or by feeding the master lens group G _M integrally, it may be performed focusing on a close object. Also, the master lens group G
_By moving (floating) the _M and the converter lens group G _C independently of each other, it is also possible to focus on a short-distance object.

According to the above embodiments, 2ω = 43.5.
It has a large angle of view of about ° and a large aperture with an F-number of about 2.8, and can continuously change spherical aberration from a negative value to a positive value, including a sharp image quality state. A possible aberration-variable optical system can be realized. With this variable aberration optical system, a beautiful soft focus image or a defocus image can be obtained, and macro photography up to 1/2 or 1/4 can be performed. Further, since the variable aberration optical system of each embodiment satisfies the condition of a large angle of view, the function of a so-called tilt shift lens can be provided by further moving the entire optical system. Also, by moving the master lens group G _M and converter lens group G _C or all groups in the direction orthogonal to the optical axis, it is also possible to realize a so-called antivibration optical system.

[0055]

As described above, according to the present invention, an aberration having a sufficiently large angle of view and capable of continuously changing the spherical aberration from a negative value to a positive value with a sharp image quality in between. A variable optical system can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration and a movement locus of a variable aberration optical system according to a first example of the present invention.

FIG. 2 is a diagram illustrating various aberrations in a normal mode in which the spherical aberration is least generated in an infinity in-focus state according to the first embodiment.

FIG. 3 is a diagram illustrating various aberrations in the soft focus mode (1) in which the first embodiment is focused on an object at infinity and has good back-blur (an image of an out-of-focus portion of the background).

FIG. 4 is a diagram illustrating various aberrations in a soft focus mode (2) according to the first embodiment in which the object is focused on infinity and front blur (image of an out-of-focus portion of the foreground) is favorable.

FIG. 5 is a diagram illustrating a configuration and a movement locus of a variable aberration optical system according to a second example of the present invention.

FIG. 6 is a diagram illustrating various aberrations in a normal mode in which the amount of spherical aberration is smallest in an infinity in-focus state according to the second embodiment.

FIG. 7 is a diagram illustrating various aberrations in a soft focus mode (1) according to a second embodiment in which the object is in focus at infinity and the back blur (image of the out-of-focus portion of the background) is favorable.

FIG. 8 is a diagram of various aberrations in the soft focus mode (2) according to the second embodiment, in which the object is focused on infinity and front blur (image of an out-of-focus portion of the foreground) is favorable.

[Explanation of symbols]

G _M master lens group G _C converter lens group L _P positive lens component L _N negative lens component L ₁ first partial lens group L ₂ second partial lens group L ₃ third partial lens group S aperture stop

Claims (10)

[Claims] 1. A master lens group G _M having a positive refractive power and a converter lens group G _C having a negative refractive power are provided in order from the object side, and the master lens group G _M is arranged in order from the object side. a first lens subunit L ₁ having a positive refractive power, a second lens subunit L ₂ having a negative refractive power, a third having a positive refractive power
And a partial lens group L _3, said converter lens group G _C has in order from the object side, a lens component L _P having a positive refractive power and a lens component L _N having a negative refractive power, the space formed between the positive lens component L _P wherein the negative lens component L _N is a concave surface with respect to the aperture stop, axial air distance D between the positive lens component L _P and a negative lens component L _N
Is a variable aberration optical system that mainly changes the spherical aberration by changing the focal length of the master lens group G _{M in} the infinity in-focus state, f _M , when the focal length of said converter lens group G _C generation amount in the smallest lens position state was f _C, aberration adjustable optical system that satisfies the conditions of _{-1 <f M / f C <} 0. 2. The focal length of the negative lens component L _N is f _N
And the converter lens group G in a focused state at infinity and in a lens position state where the amount of spherical aberration generated is the least.
_{2. The} variable aberration optical system according to claim 1, wherein a condition 0 <f _N / f _C <1 is satisfied when a focal length of _C is f _C. 3. When the Abbe number of the negative lens in the negative lens component L _N is ν _N and the Abbe number of the positive lens in the positive lens component L _P is ν _P , -10 <ν _N −ν _The variable aberration optical system according to claim 1, wherein a condition of _P <30 is satisfied. 4. The radius of curvature of the object-side surface of the negative lens located closest to the object in the negative lens component L _N is defined as rb,
When said positive lens component L _P Most positioned on the image side positive lens ra curvature radius of the image side surface of in, satisfies -1 <(rb -ra) / ( rb + ra) <0 condition The variable aberration optical system according to claim 1, wherein: 5. The d of the negative lens in the negative lens component L _N
The refractive index for the line and n _N, wherein when the refractive index at the d-line of the positive lens of the positive lens in the component L _P was n _P, satisfies the condition -0.25 <n _N -n _P <0.35 The variable aberration optical system according to any one of claims 1 to 4, wherein: 6. The radius of curvature of the object side surface of the positive lens component L _P and rc, when the radius of curvature of an image side of the positive lens component L _P and rd, -10 <(rd + rc ) 6. The variable aberration optical system according to claim 1, wherein a condition of / (rd-rc) <1 is satisfied. 7. When the radius of curvature of the object-side surface of the negative lens component _LN is re, and the radius of curvature of the image-side surface of the negative lens component _LN is rf, -1 <(rf + re) / The variable aberration optical system according to any one of claims 1 to 6, wherein a condition of (rf-re) <10 is satisfied. By 8. varying the axial distance D of the positive lens component L _P wherein the negative lens component L _N, changing the spherical aberration from a negative value to a positive value include a minimum value The variable aberration optical system according to claim 1, wherein the variable optical focus lens is a variable soft focus lens. Wherein said first lens subunit L ₁ has two positive lenses, the second lens subunit L ₂ has one negative lens, the third lens subunit L ₃ is 9. The variable aberration optical system according to claim 1, further comprising a positive lens, a cemented lens of a negative lens and a positive lens, and a positive lens. 10. The variable aberration optical system according to claim 1, wherein each of the positive lens component L _P and the negative lens component L _N includes one lens.