JPH10123417A - Zoom optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a finite system zoom lens high in performance, long in back and high in variable power to utilize it widely by specifying the relation between a distanced from a first lens surface to an image surface and the distance from a final lens surface to the image surface. SOLUTION: A whole system is constituted of five or more groups in total, and zoom variable power part is constituted of a second to a fourth groups G2-G4 out of them. Thus, the zoom variable power part is constituted of the variable power groups G2-G4 of three or more groups out of lens groups G1-G5, and when the magnification of the zoom variable power part is nearly unmagnified, the magnification borne by each variable power lens group is made nearly unmagnified. Then, when the distance from the first lens surface to the image surface (namely the entire length of a zoom optical system) is made as TL and the distance from the final lens surface to the image surface (namely back focus) is made as BF, the condition meant by BF/TL>=0.25 is satisfied. Thus, a power arrangement having excellent variable power efficiency is selected, and a high variable power ratio is secured, so that an optical system having a large zoom ratio is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a zoom lens.

[0002]

2. Description of the Related Art Heretofore, a finite optical system has been often used in various electronic image apparatuses which require photographing and projection by an optical system in inputting and outputting an image. Specifically, it is used for a digital still camera lens system, a close-up photographing optical system, an enlargement / expansion optical system, a reduction optical system, and a projection lens for a liquid crystal video projector. In particular, a finite single focus lens is poor in versatility, and a dedicated optical system is used for each purpose. On the other hand, a finite zoom lens has higher versatility than a single focus lens, but has few types of lenses. For this reason, lens systems for 35 mm still cameras, 16 mm cines, and TVs have often been used.

[0003]

An optical system used for an electronic image device or the like is required to have specifications corresponding to a very large number of purposes. Dedicated optical systems have been provided for various purposes. For this reason, it is necessary to design an optical system in proportion to the target number. This is very inefficient and uneconomical. In order to solve these problems, the present invention provides a high-performance, high-magnification zoom lens having a long back focus, such as that used for a liquid crystal projector, and facilitates an optical system system suitable for a wide range of applications. To provide. In order to provide an optical system that requires a high resolution, there has been a demand for an optical system that corrects chromatic aberration of magnification, has high performance, and has little distortion in zooming. Further, there has been a demand for an optical system that secures a sufficient amount of peripheral light around the screen in order to reduce shading. An object of the present invention is to provide an optical system that satisfies these requirements simultaneously.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. That is, the whole system is constituted by five or more lens groups, and three or more of the lens groups are provided. In a zoom optical system in which a zoom variable power unit is configured by the variable power lens unit and the magnification of the variable power lens unit is substantially the same when the zoom power of the zoom power unit is substantially the same, The distance from one lens surface to the image surface (ie, the total length of the zoom optical system) is TL, and the distance from the final lens surface to the image surface (ie, the back focus) is BF.
BF / TL ≧ 0.25 (1) The zoom optical system is characterized by satisfying the following condition:

FIG. 1 shows a moving trajectory of each lens group during zooming in a typical basic configuration of the present invention. In this configuration, the entire system is composed of a total of five groups, of which the second
The fourth to fourth lens groups constitute a zoom magnification unit.
Assuming that the lateral magnification of each lens group is β _i (i = 1 to 5), the combined imaging magnification of the entire system is β, and the magnification of the zoom magnification changing unit is β _z , β = β ₁ β ₂ β ₃ β ₄ β ₅ β _z = β ₂ β ₃ β _{4 In} the present invention, at a specific zooming position c, the magnification of any zoom lens group i (i = 2 to 4) is | β _c2 | ≒ 1, | β _c3 | ≒ 1, | β _c4 | ≒ 1 (A). As a result, at this simultaneous equal-magnification zooming position c, | β _cz | = | β _c2 β _c3 β _c4 | ≒ 1.

In general, among the solutions satisfying the zoom equation, when the magnification of the variator group is the same (β _i = −1), the magnification of the compensator group is also the same (β _i = −1). Since the two movement curves of the compensator group (the solution curve of the zoom trajectory) are connected in an arrangement of the same size (β _i = −1), the trajectory can be mutually changed. The present invention positively utilizes the change of the orbit, and the magnification of the variable power lens group that constitutes the zoom variable power unit is adjusted at a specific zooming position.
At the same time, it is configured so as to have the same magnification (-1X). As a result, a zoom trajectory (zoom equation solution) that can be reliably employed over the entire zoom region can be stably obtained.

In the present invention, as shown in FIG. 1, it is preferable that the zooming position c satisfying the above equation (A) is between the wide-angle end w and the telephoto end t. However, the present invention includes a case where the zooming position c at which the expression (A) holds is on the lower magnification side than the wide-angle end w or on the higher magnification side than the telephoto end t.

In the present invention, when the magnification of the zoom magnification unit is a reduction magnification, it is preferable that all magnifications carried by the respective magnification lens units are reduction magnifications. When is a magnification, it is preferable that each magnification carried by each variable power lens unit is a magnification. FIG.
In the example shown in FIG. 7, at a specific zooming position c between the wide-angle end w and the telephoto end t, | β _ci | ≒ 1 (i = 2 to 4, and thus | β _cz | ≒
1) It is configured to be as follows. Therefore, at the wide-angle end w and the telephoto end t, | β _wi | ≦ 1 (i = 2 to 4, and thus | β _wz | ≦
1) | β _ti | ≧ 1 (i = 2 to 4, thus | β _tz | ≧
1) It is preferable to configure the following.

As described above, the case where the zooming position c at which the expression (A) is satisfied is on the lower magnification side than the wide-angle end w is also included in the present invention. In this configuration, | β _ti | > | Β _wi |> | β _ci || 1 (i = 2 to 4, thus | β _tz |> | β _wz |> | β _cz
| ≒ 1) is preferable. Similarly, (A)
The present invention includes a case where the zooming position c where the expression is satisfied is higher than the telephoto end t. In this configuration, | β _wi | <| β _ti | <| β _ci | ≒ 1 ( i = 2 to 4, thus | β _wz | <| β _tz | <| β _cz
| ≒ 1) is preferable.

With these arrangements, it is possible to select a zoom power arrangement with very high zooming efficiency, so that a high zooming ratio can be secured, that is, an optical system with a large zoom ratio can be achieved. In the present invention, since the zoom magnification changing unit is constituted by three or more lens groups, this effect is accelerated.

As described above, in the present invention, a zoom power arrangement having high zooming efficiency is achieved by making the zoom zooming unit multiple-units at the same time, but at the same time, for example, an optical system for a liquid crystal projector. When used as a system, it is necessary to arrange a color separation optical system such as a dichroic mirror or a dichroic prism or a color combining optical system between the final lens surface and the image forming surface. Equation (1) is a requirement for this. If the expression (1) is not satisfied, it is difficult to put the color separation optical system and the color combining optical system in the back focus.

As a method for extending the back focus, assuming that the entire system has five groups, the refractive power of the fourth lens group is increased, the refractive power of the fifth lens group is reduced, and the fifth lens group is reduced. A method of increasing the magnification | β ₅ | of the lens group can be considered. However, increasing the refractive power of the fourth lens group imposes a large load on the fifth lens group whose refractive power is to be reduced, making it difficult to correct aberrations. Reducing the refractive power of the fifth lens group causes an increase in the size of the lens system, and also increases the principal ray height passing through the fifth lens group, thereby increasing the lens diameter.
If the magnification β ₅ of the fifth lens group is further increased, interference with the fourth lens group is caused, and the magnification β _c of the entire system at the same magnification is increased. Interference occurs between the two lens groups, making it difficult to increase the width and zoom. Therefore, these values must be kept in the optimal range.

In the present invention, the sign of the refractive power of each lens group is preferably symmetric between the lens group arranged from the object side and the lens group arranged from the image side.
That is, assuming that the configuration of the entire system is all N groups, the first lens group and the N-th lens group have the same sign of the refractive power, and likewise the second lens group.
It is preferable that the sign of the refractive power of the lens group is the same as that of the (N-1) th lens group. When the total number of lens groups is odd, the lens groups are located at the center. Therefore, the sign of the refractive power of each lens group on the object side of the central lens group and the sign of the refractive power of each lens group on the image side of the central lens group should be symmetrical with respect to the central lens group. preferable. When the total number of lens groups is even, the air gap is located at the center. Therefore, the sign of the refractive power of each lens group on the object side of the center air gap and the sign of the refractive power of each lens group on the image side of the center air gap should be symmetrical with respect to the center air gap. preferable.

As a method of reducing the distortion, a lens configuration having high symmetry in the lens shape and the refractive power arrangement regarding the aperture stop can be considered. At the center of an optical system having such a symmetry, a lens group does not necessarily have to exist, as in the case where N is an even number. In a zoom lens in which a lens group forming perfect symmetry moves, correction of fluctuation of distortion should not be desired. However, in order to obtain an optical system with little distortion by zooming, it is preferable that the refractive power distribution configuration of each lens group has a certain degree of symmetry with respect to the aperture stop.

For example, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power,
And a fifth lens group having a positive refractive power, wherein the second lens group, the third lens group, and the fourth lens group have substantially the same magnification (-1X) at the same time. To When analyzing the state of occurrence of distortion in the zoom optical system, it is desirable to consider the zoom optical system as a whole divided into three parts.

That is, if the lens group including the aperture stop is the middle group, the object side of the middle group is the front group, and the image side of the middle group is the rear group, the interior of each of the front group and the rear group has a considerable degree. It is necessary to have a refractive power configuration and a lens configuration that can correct distortion up to this point. These uncorrected components in the front group and the rear group, and the components that could not be offset in the front group and the rear group, are corrected in the middle group and assigned to roles. By using an optical system having such a lens configuration, it can be understood that even an optical system having a lens group that moves during zooming can have a configuration with little variation with respect to distortion. On the other hand, in order to greatly reduce the distortion, the refractive power distribution inside each of the front group and the rear group is also positive, negative or negative, positive, a lens configuration capable of canceling the aberration,
It is preferable to use a refractive power distribution.

Further, in the present invention, it is preferable to provide a focusing lens group separately from the zoom magnification changing section. In general, in a finite distance optical system, it is desirable to dispose the focusing lens group on the object side of the zoom magnification unit. This is because a change in the photographing distance and a focus shift can be easily suppressed by the zoom magnification changing unit. By arranging the focusing lens group closest to the object side and configuring the lens group in a multi-group configuration, a short-distance correction mechanism and a degree of freedom in correcting performance degradation due to zooming at different conjugate lengths are secured. be able to. As the simplest configuration, by extending only the first lens group to the object side,
Focusing is possible, and it is possible to change a desired photographing distance, a zoom magnification range, and the like.

Further, a so-called micro-zoom optical system can be realized by arranging the sign of the refractive power of each lens group symmetrically between the object side and the image side and having a focusing lens mechanism. It is possible to correct performance degradation due to zoom magnification at different conjugate lengths. As a result, it is possible to easily change the desired photographing distance, the area of the zoom magnification, and the like, and realize an optical system having a wide range of use.

When the entire system is composed of five groups and the variable power lens group is composed of the second to fourth lens groups, the magnification β ₂ carried by each lens group of the zoom variable power unit other than the focusing lens group. ~
β ₄ satisfies the simultaneous equal-size arrangement as shown in the formula (A) and more preferably falls within the following range. It is more desirable that the magnification β ₅ carried by the fifth lens group is set in the following range. −1.3 <β ₂ <−0.5 (2) −1.3 <β ₃ <−0.6 (3) −1.2 <β ₄ <−0.7 (4) −1.7 < β ₅ <−0.7 (5)

If the upper limit of the expression (2) is exceeded, the first lens group and the second lens group interfere with each other, and at the same time, the incident height of the principal ray at the outermost periphery of the screen passing through the first lens surface is significantly separated from the optical axis. This causes an increase in the lens diameter. Further, it is difficult to correct the outer coma aberration of the lower beam of the principal ray at the wide angle end. Below the lower limit, the second lens group and the third lens group interfere with each other and are inappropriate. When the value exceeds the upper limit of the expression (3), the first value is obtained at the wide-angle end.
At the same time as the incident height of the principal ray at the outermost part of the screen passing through the lens surface is significantly separated from the optical axis, causing an increase in the lens diameter,
The second lens group and the third lens group interfere with each other and are inappropriate. If the lower limit is exceeded, it becomes difficult to correct spherical aberration at the telephoto end, and at the same time, the third lens unit and the fourth lens unit interfere with each other, which is inappropriate. When the value exceeds the upper limit of the expression (4), the incident height of the principal ray at the outermost periphery of the screen passing through the first lens surface at the wide-angle end is remarkably separated from the optical axis, and the lens diameter is increased.
The third lens group and the fourth lens group interfere with each other and are inappropriate. If the lower limit is exceeded, it is difficult to correct the outer coma aberration above the principal ray, and at the same time, the fourth lens group and the fifth lens group interfere with each other, which is inappropriate. When the value exceeds the upper limit of the expression (5), the incident height of the principal ray at the outermost periphery of the screen passing through the first lens surface at the wide-angle end is significantly separated from the optical axis, resulting in an increase in the lens diameter and a desired back focus. It is impossible to obtain and is inappropriate. If the lower limit is exceeded, it is difficult to correct the outer coma aberration above the principal ray, and at the same time, the fourth lens group and the fifth lens group interfere with each other, which is inappropriate.

Here, the lens arrangement in which the second to fourth lens groups satisfy the same magnification at the same time does not require mathematical rigor, and even if the lens arrangement is near this simultaneous magnification arrangement. Good. That is, a rounding error, a magnification error range that causes a defocus such as a depth of focus on the image forming plane such as a manufacturing tolerance, and an error range due to adjustment are naturally allowed. Therefore, it also includes a zoom arrangement area that is approximately the same size at the same time within the allowable range. This is because even if an area where no zoom solution exists near the same-magnification arrangement occurs, there is no practical problem as long as the zoom area that causes a jump in focus on the image plane is small.

As a guide of a desirable allowable range, one of the zoom lens groups, that is, the j-th lens group (j = 2 to 4)
When magnification beta _cj is magnification of (-1X), other lens group i (i = 2~4, i ≠ j) plays magnification beta _ci is acceptable if it is within the scope of the formula. 0.9 <| _βci | <1.1 (6) When the upper limit of the expression (6) is exceeded, the area where no zoom solution exists from the telephoto end increases, and the area where focus is fixed by zooming becomes narrower. It is inappropriate. If the lower limit is exceeded, the area where the zoom solution does not exist increases from the wide-angle end, and the area where the focus is fixed by zooming becomes narrow, which is inappropriate. If the area without the zoom solution is widened, the area where continuous zooming cannot be achieved increases, and the practicability is remarkably reduced.

In the case where the entire system is composed of five groups and the variable power lens group is composed of the second to fourth lens groups, it is preferable to satisfy the following expression. 0.03 <β ₁ / β ₅ <0.1 (7) 0.7 <f ₂ / f ₄ <1.3 (8) −0.8 <f ₄ / f ₅ <−0.6 (9) When the value exceeds the upper limit of the expression (7), the back focus becomes short, and the working distance to the object point becomes short. It is not suitable because it is difficult to secure desired magnification and working distance as a finite system. If the lower limit is exceeded, the working distance becomes unnecessarily long, which is unsuitable for use as a finite system. However, when used as an infinity system, it is easy to suppress the wide-angle end and arrange the focusing lens groups so as to be an infinity system. At this time, the lower limit can be set to 0.

If the upper limit of the expression (8) is exceeded, the amount of movement of the second lens unit increases and interferes with the other lens units, reducing the zooming efficiency. Therefore, it is inappropriate for obtaining a high zooming zoom. . In addition, the refractive power of the third lens group becomes too strong, and the load on the fifth lens group increases, making it difficult to correct coma aberration above the principal ray, which is inappropriate. If the lower limit is exceeded, the refracting power of the second lens group becomes too strong, so that the telephoto end can be widened and the magnification can be increased. The height is not appropriate because the height is significantly separated from the optical axis and the lens diameter is increased. Also, it becomes difficult to correct various aberrations such as spherical aberration and coma.

When the value exceeds the upper limit of the expression (9), the exit height of the principal ray passing through the fifth lens unit becomes large, which results in an increase in the lens diameter. At the same time, the refractive power of the fourth lens unit becomes too strong. The load on the fifth lens group increases, and it becomes difficult to correct coma aberration above the principal ray, which is inappropriate. If the lower limit is exceeded, it becomes difficult to obtain a desired back focus, and at the same time, the operation interval of the fourth lens group is shortened and interferes with other lens groups to reduce the zooming efficiency. Is unsuitable for

[0026]

Embodiments of the present invention will be described.
FIGS. 2, 6, 10 and 14 are lens configuration diagrams of first, second, third and fourth embodiments of the zoom optical system according to the present invention, respectively. In all the embodiments, in order from the object side, a first lens group G ₁ having a positive refractive power, a second lens group G ₂ having a negative refractive power, a third lens group G ₃ having a positive refractive power, a negative lens group Is a zoom lens including a fourth lens group G ₄ having a positive refractive power and a fifth lens group G ₅ having a positive refractive power. The first lens group G ₁ is capable of focusing by moving toward the object side, it is possible to change information such as the shooting distance, zooming magnification of the region. The second lens group G ₂ is a compensator group, the third lens group G ₃ is the main lead group, the fourth lens group G ₄ is a secondary lead group. In zooming, the second lens group G ₂ , the third lens group G ₃ ,
And the fourth lens group G ₄ moves in the optical axis direction in a mutually dependent manner. The fifth lens group G ₅ is a fixed lens group to the image plane, the major lens group that determine the length and the exit pupil position of the back focus.

Tables 1 to 4 show data of the first to fourth embodiments. In the [Overall Specifications] of each table, ω represents a half angle of view. In [Lens Specifications], the first column is the number of the lens surface from the object side,
Column r is the radius of curvature of each lens surface, third column d is the distance between each lens surface, fourth column ν _d is the Abbe number based on the bright line spectrum d line (reference wavelength λ = 587.6 nm) of each lens, refractive index column 5 n _d to against the d line of each lens, at column 6 represents the lens number. Further, as shown in [Focal length and magnification of each lens group] and [Conditional value] in each table, each embodiment is formed so as to satisfy each of the conditional expressions (1) to (9).

The first embodiment has a lens configuration of 17 elements in 12 groups except for a filter with a zoom ratio of 3 times. The first lens group G ₁ includes a filter L ₁ having a plane parallel to the object side, a negative meniscus lens L ₂ having a convex surface having a small curvature toward the object side, and a positive lens L ₃ having a convex surface having a strong curvature facing the object side. a positive lens L ₂ L ₃ consisting of bonding, and a positive meniscus lens L ₄ with its stronger curvature convex surface facing the object side. Second lens group G
_2, toward a negative meniscus lens L ₅ toward a weak convex of curvature at the object side, a negative meniscus lens L ₆ toward a weak convex with curvature across product side an air space, the curvature weak concave surface facing the object side and a positive meniscus lens L ₇ and consists of bonding of the negative meniscus lens L ₈ with its stronger curvature concave surface facing the object side a negative lens L ₇ L ₈ Prefecture. The third lens group G ₃ is composed of a negative meniscus lens with its stronger curvature concave surface facing the positive meniscus lens L ₉ and the object side toward the curvature weak concave surface facing the object side L ₁₀
A positive lens L ₉ L ₁₀ consisting of bonding with, a biconvex lens L ₁₁ with its stronger curvature convex surface facing the object side. The fourth lens group G ₄ is composed of a negative lens L ₁₂ L ₁₃ consisting of lamination of a biconvex lens L ₁₂ and a biconcave lens L _13, a negative meniscus lens with its strong concave surface curvature in spaced product side air gap L ₁₄
Consists of The fifth lens group G ₅ includes a positive meniscus lens L ₁₅ with its curvature weak concave surface facing the object side, a positive lens L ₁₆ L consisting of bonding of a biconcave lens L ₁₆ and a biconvex lens L _17
17, a biconvex lens L _18.

[0029]

[Table 1]

In the second embodiment, the zoom ratio is three times, and the lens configuration of the eleven groups is sixteen except for the filter. The first lens group G ₁ includes a filter L ₁ having a plane parallel to the object side, a negative meniscus lens L ₂ having a convex surface having a small curvature toward the object side, and a positive lens L ₃ having a convex surface having a strong curvature facing the object side. a positive lens L ₂ L ₃ consisting of bonding, and a positive meniscus lens L ₄ with its stronger curvature convex surface facing the object side. Second lens group G
_2, a negative meniscus lens L ₅ toward a weak convex of curvature at the object side, consisting of bonding of the positive meniscus lens L ₆ toward a weak concave surface curvature in spaced product side an air space and a biconcave lens L ₇ It consists of negative lenses L _{6 and} L ₇ . Third lens group G
₃ is a positive lens L ₈ L _{9 formed} by bonding a biconvex lens L ₈ and a negative meniscus lens L ₉ having a concave surface with a strong curvature on the object side, and a positive lens L ₁₀ having a convex surface with a strong curvature on the object side. Consists of The fourth lens group G ₄ is composed of a negative lens L ₁₁ L ₁₂ consisting of bonding of the positive meniscus lens L ₁₁ with its curvature weak concave surface facing the object side and a biconcave lens L _12, the curvature on the object side an air space negative a strong concave surface facing the meniscus lens L ₁₃
Consists of The fifth lens group G ₅ includes a positive meniscus lens L ₁₄ with its curvature weak concave surface facing the object side, a positive lens L ₁₅ L consisting of bonding of a biconcave lens L ₁₅ and a biconvex lens L _16
16, a biconvex lens L _17.

[0031]

[Table 2]

The third embodiment has a zoom ratio of 3 times and a lens configuration of 16 elements in 11 groups excluding a filter. The first lens group G ₁ includes a filter L ₁ having a plane parallel to the object side, a negative meniscus lens L ₂ having a convex surface having a small curvature toward the object side, and a positive lens L ₃ having a convex surface having a strong curvature facing the object side. a positive lens L ₂ L ₃ consisting of bonding, and a positive meniscus lens L ₄ with its stronger curvature convex surface facing the object side. Second lens group G
_2, a negative meniscus lens L ₅ toward a weak convex of curvature at the object side, consisting of bonding of the positive meniscus lens L ₆ toward a weak concave surface curvature in spaced product side an air space and a biconcave lens L ₇ It consists of negative lenses L _{6 and} L ₇ . Third lens group G
₃ is a positive lens L _{8 formed by} bonding a biconvex lens L ₈ and a negative meniscus lens L ₉ having a concave surface with a strong curvature on the object side.
And L _9, a positive lens L ₁₀ with stronger curvature convex surface facing the object side. The fourth lens group G ₄ is composed of a negative lens L ₁₁ L ₁₂ consisting of bonding of the positive meniscus lens L ₁₁ with its curvature weak concave surface facing the object side and a biconcave lens L _12, strong product side an air space a negative meniscus lens L ₁₃ with a concave surface. The fifth lens group G ₅ is composed of a lamination of a positive meniscus lens L ₁₄ with its curvature weak concave surface facing the object side, a negative meniscus lens L ₁₅ having a weak convex of curvature at the object side and a biconvex lens L ₁₆ It comprises a positive lens L ₁₅ L ₁₆ and a biconvex lens L ₁₇ .

[0033]

[Table 3]

In the fourth embodiment, the zoom ratio is three times, and the lens configuration is composed of 16 elements in 11 groups except for the filter. The first lens group G ₁ includes a filter L ₁ having a plane parallel to the object side, a negative meniscus lens L ₂ having a convex surface having a small curvature toward the object side, and a positive lens L ₃ having a convex surface having a strong curvature facing the object side. a positive lens L ₂ L ₃ consisting of bonding, and a positive meniscus lens L ₄ with its stronger curvature convex surface facing the object side. Second lens group G
_2, a negative meniscus lens L ₅ toward a weak convex of curvature at the object side, consisting of bonding of the positive meniscus lens L ₆ toward a weak concave surface curvature in spaced product side an air space and a biconcave lens L ₇ It consists of negative lenses L _{6 and} L ₇ . Third lens group G
Reference numeral ₃ denotes a positive lens L ₈ L formed by bonding a biconvex lens L ₈ and a negative meniscus lens L ₉ having a strong concave surface on the object side.
_9, a biconvex lens L ₁₀ with stronger curvature convex surface facing the object side. The fourth lens group G ₄ is composed of a negative lens L ₁₁ L ₁₂ consisting of bonding of the positive meniscus lens L ₁₁ with its curvature weak concave surface facing the object side and a biconcave lens L _12, strong product side an air space a negative meniscus lens L ₁₃ with a concave surface. The fifth lens group G ₅ is composed of a lamination of a positive meniscus lens L ₁₄ with its curvature weak concave surface facing the object side, a negative meniscus lens L ₁₅ having a weak convex of curvature at the object side and a biconvex lens L ₁₆ It comprises a positive lens L ₁₅ L ₁₆ and a biconvex lens L ₁₇ .

[0035]

[Table 4]

FIGS. 3, 4 and 5 show the spherical aberration at the wide angle end, the intermediate magnification position, and the telephoto end, respectively, of the first embodiment.
Shows astigmatism, distortion, chromatic aberration of magnification, and lateral aberration.
In each aberration diagram, NA represents a numerical aperture, Y represents an image height, d represents a d-line, and g represents a g-line (λ = 435.8 nm). In the astigmatism diagram, a dotted line M represents a meridional image plane, and a solid line S represents a sagittal image plane. Similarly, FIGS. 7, 8 and 9 show various aberrations of the second embodiment, FIGS. 11, 12 and 13 show various aberrations of the third embodiment, and FIGS. 15, 16 and 17 show aberrations. 14 shows various aberrations of the fourth example.

In any of the embodiments, especially at the wide-angle end, the distortion is almost completely corrected.
Since it depends on s ⁴ ω, it is necessary to suppress bignetting. As is clear from the aberration diagrams, in each of the embodiments, a sufficient peripheral light amount is secured. Since the peripheral light amount is large, the coma because aberration fluctuations suppressed from occurring in zooming, especially lower coma measures lens arrangement of the second lens group G ₂ of the principal rays, lens shape, and the third lens group G ₃
The lens shape has been devised. On the other hand, the lens arrangement of the fifth lens group G ₅ in the upper coma measures of the principal ray,
The lens shape is considered.

The fourth lens group G ₄ and the fifth lens group G ₅
By increasing the number of laminated lenses,
Sufficient freedom to simultaneously correct axial chromatic aberration and lateral chromatic aberration at the wide-angle end can be ensured. In this case it is possible to reduce the load for the second lens group G ₂ achromatic. Furthermore, embodiments of the present invention are constituted by the lens system 5-group configuration, the third lens group G ₃ is divided into two groups, be easily realized by a lens system 6 groups constituting the entire system it can. Similarly by dividing the third lens group G ₃ into three groups a structure that ensures the freedom of large diameter can be easily realized by a lens system of the entire seven groups configuration.

It is apparent that the embodiment of the present invention can reduce the number of constituent lenses when the widening is unnecessary or when the objective is sufficiently achieved with a dark optical system. In particular, it is much easier to enlarge the zoom region to the telephoto end and increase the zoom ratio than to expand to the wide-angle end. Further, shortening the conjugate length and increasing the photographing magnification can be easily realized from the present invention because it is not necessary to increase the width. The first lens group G ₁ can be achieved by moving the object side as one way to achieve this.

Although the focusing lens group G ₁ is fixed in the embodiment in zooming, it may be moved so as to contribute to zooming in zooming. And focusing lens group G ₁ is composed of a plurality of lens groups, it is easy to adopt a configuration having a variety of short-range correction mechanism, such as floating. When five or more zooming units are provided, it is not always necessary for all the zooming units carried by the zooming unit to be at the same magnification. A specific zooming group may be used avoiding the same magnification arrangement.

Further, according to the present invention, the effective F value is 3.5 at the wide angle end.
In this case, the peripheral light amount is sufficiently ensured, the effective diameter of the first lens surface is reduced, and the optical system is compact. In spite of this, it is considered that the reason why the various types of aberration can be satisfactorily corrected and a high-performance optical system can be realized is an efficient zoom type. Magnification of each group, distribution of refractive power of each lens group, clever selection of zoom trajectory, and the like.

Normally, when the pupil is made as close as possible to the surface of the lens end, the refractive power arrangement of the lens groups is preceded by the lens group having a negative refractive power. On the other hand, when the position of the pupil is as far as possible from the surface of the lens end, the refractive power arrangement of the lens groups is preceded by the lens group having a positive refractive power. By employing such a refractive power distribution, an image-side, object-side telecentric optical system, or an optical system close thereto can be realized. However, in the present invention, it is not necessary to be a strict telecentric optical system. The aperture stop may be at any position from between the second lens group and the third lens group to between the fourth lens group and the fifth lens group. Also, it may be spatially moved or fixed in conjunction with zooming.

Further, the zoom lens is opened to the zoom trajectory, and the second lens group,
As a supplement to the lens arrangement in which the third lens group and the fourth lens group satisfy the same magnification at the same time (multi-group simultaneous equal-magnification arrangement), it is also possible to express Expression (6) with another stricter standard. That is, when the magnification of any of the variable power lens groups is the same magnification (-1X), it is permissible if the combined magnification carried by the variable power lens group is within the range of the following equation. 0.95 <| β _c2 β _c3 β _c4 | <1.05 If the upper limit of the above expression is exceeded, the area where no zoom solution exists from the telephoto end increases, and the area where the focus is fixed by zooming becomes narrower. Improper. If the lower limit is exceeded, the area where the zoom solution does not exist increases from the wide-angle end, and the area where the focus is fixed by zooming becomes narrow, which is inappropriate. If these areas without the zoom solution are widened, continuous zooming cannot be achieved. However, if only the wide-angle area and the telephoto area are adopted for discontinuous use and the intermediate area is unnecessary,
The lower limit necessarily changes, and it is clear that the area where the zoom solution does not exist expands and is worth using.

[0044]

According to the present invention, the above-described high performance,
By providing a zoom lens with a long back focus and a finite high magnification, an optical system suitable for a wide range of applications can be easily provided. Further, an optical system in which distortion and fluctuation of distortion are very small by zooming can be realized. In addition, an optical system in which a sufficient amount of peripheral light is secured around the screen in order to reduce shading of the image pickup system was realized. The realization of an optical system that satisfies these characteristics at the same time greatly increases the versatility of the optical system. In addition, the size of the photographed image and the projected image, the conjugate length,
The working distance can be easily set by moving and focusing the focusing lens group, and can be used in an optimal arrangement according to various usage purposes. Specifically, this optical system is used for a document lens system, a camera-type scanner, a digital still camera lens system, a TV camera lens system, a close-up photographing optical system, an enlargement / expansion optical system, a projection lens for a liquid crystal video projector, and the like. Can be used.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the principle of the present invention.

FIG. 2 is a lens arrangement diagram at a wide-angle end according to a first embodiment.

FIG. 3 is a diagram showing various aberrations of the first embodiment at the wide-angle end.

FIG. 4 is a diagram showing various aberrations of the first embodiment at an intermediate magnification position.

FIG. 5 is a diagram showing various aberrations at the telephoto end of the first embodiment.

FIG. 6 is a lens arrangement diagram at the wide-angle end according to a second embodiment.

FIG. 7 is a diagram showing various aberrations of the second embodiment at the wide-angle end.

FIG. 8 is a diagram illustrating various aberrations of the second embodiment at an intermediate magnification position.

FIG. 9 is a diagram showing various aberrations at the telephoto end of the second embodiment.

FIG. 10 is a lens arrangement diagram at the wide-angle end according to a third embodiment.

FIG. 11 is a diagram showing various aberrations of the third embodiment at the wide-angle end.

FIG. 12 is a diagram illustrating various aberrations of the third embodiment at an intermediate magnification position.

FIG. 13 is a diagram showing various aberrations at the telephoto end of the third embodiment.

FIG. 14 is a lens arrangement diagram at the wide-angle end according to a fourth embodiment.

FIG. 15 is a diagram showing various aberrations of the fourth embodiment at the wide-angle end.

FIG. 16 is a diagram illustrating various aberrations of the fourth embodiment at an intermediate magnification position.

FIG. 17 is a diagram showing various aberrations at the telephoto end of the fourth embodiment.

[Explanation of symbols]

G ₁ … first lens group G ₂ … second lens group G ₃ … third lens group G ₄ … fourth lens group G ₅ … fifth lens group S… stop

Claims (4)

[Claims] The zoom lens system comprises a zooming unit comprising three or more lens units, and a zooming unit comprising at least three zooming lens units. In a zoom optical system in which the magnifications of the variable magnification lens groups are almost equal at the same magnification, the distance from the first lens surface to the image surface is TL, and the distance from the last lens surface to the image surface is TL. A zoom optical system that satisfies a condition of BF / TL ≧ 0.25 where BF is a distance. 2. The zoom optical system according to claim 1, wherein the zooming position at which the magnification of the zoom magnification unit is substantially equal is between the wide-angle end and the telephoto end. 3. The zoom according to claim 1, wherein the sign of the refractive power of each lens group is symmetric between the lens group arranged from the object side and the lens group arranged from the image side. Optical system. 4. The zoom optical system according to claim 1, further comprising a focusing lens unit which moves in the optical axis direction when focusing.