JPH05341186A - Limited distance zoom lens system - Google Patents

Abstract

PURPOSE:To provide a limited-distance zoom lens system consisting of three groups of lenses (negative, positive, positive) and having a zooming ratio of 2.5(X). CONSTITUTION:A limited-distance zoom lens system comprises a first negative lens group I consisting of positive lenses and at least one negative lens, a second positive lens group II consisting of at least one positive lens and at least one negative lens, and a third positive lens group III consisting of at least one positive lens and at least one negative lens, the groups I-III being disposed in sequence from the magnification side; a diaphgram S is disposed from the magnifying end to the contracting end of the first negative lens group I, and the first negative lens group I and the diaphragm S are fixed as zooming progresses from the end of the longest focal distance to the end or the shorteset focal distance, and the second positive lens group II and the third positive lens group III increase the interval between the second positive lens group II and the third positive lens group III, and then move toward the contraction side in a monotone fashion while contracting the interval.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable power optical system for copying, which performs variable power with a fixed conjugate length.
A high-magnification zoom lens system with a zoom ratio of 2.5 times, which is a lens group configuration in which a diaphragm is arranged in the vicinity of the first negative lens group I and an image rotating prism such as a doped prism arranged in the optical path is downsized. Is.

[0002]

2. Description of the Related Art An optical path diagram of a microfilm reader is shown in FIG.
6 shows. That is, the image of the microfilm 1 is projected by the projection lens system 2 into the image rotation prism 3, the reflecting mirrors 4, 5, and 6.
It is projected on the screen 7 through the and observed. Lens systems used in such microfilm readers, microfilm printers, and microfilm reader printers are those disclosed in Japanese Patent Publication No. 47-35028, Japanese Patent Publication No. 57-4016, and Japanese Patent Publication No. 57-7371.
The one disclosed in Japanese Patent No. 5 is known. However, the Japanese Examined Sho 47-
The one disclosed in JP-A-35028 and the one disclosed in JP-A-57-4016 are microlens systems having a constant magnification, so that the framing is constant and the usability is poor. On the other hand, JP-A-57-73
Although the one disclosed in Japanese Patent No. 715 is a zoom lens system for a finite distance, since the diaphragm is incorporated in the lens system,
There is a problem in that the effective F number on the enlargement side (screen side) changes due to zooming and the amount of light on the screen surface fluctuates greatly, giving a visually uncomfortable feeling.

Therefore, the inventor of the present invention has, for example, disclosed in Japanese Patent Laid-Open No.
JP-A-2-237415 and JP-A-62-23741.
A front aperture finite zoom lens system as disclosed in Japanese Patent No. 6 has been proposed.

[0004]

The present invention is based on FIG.
As shown in FIGS. 2A and 2B and FIGS. 2A and 2B, the first negative lens group I of the fixed lens group and the second positive lens group II of the movable group including the diaphragm S from the enlargement side. And the third positive lens group III, and the second positive lens group II and the second positive lens group II and the third positive lens group III are connected with zooming from the longest focal length end (hereinafter referred to as the L end) to the shortest focal length end (hereinafter referred to as the S end). The third positive lens group III is characterized by being moved to the reduction side.

As described above, in order to minimize the image rotation prism 3 such as a doped prism arranged in the optical path, and to suppress the fluctuation of the spread of the off-axis light beam on the magnifying side end face even during zooming, the diaphragm is used. S is fixed regardless of zooming.

In the prior art examples disclosed in Japanese Patent Laid-Open No. 62-237415 and Japanese Patent Laid-Open No. 62-237416, the zoom ratio is 1.5 times as shown in the paraxial layout diagram in FIG. Since it is relatively small as follows, a fixed lens is not arranged at the magnifying end of the lens system, and only the fixed diaphragm S is arranged.

However, when the magnification range aimed at by the present invention becomes as large as about 2 times, the moving distance of the first lens group I is too large in the lens system of the type based on the positive and negative two-group zoom. Then, when the diaphragm S is fixed, the position of the chief ray having the maximum angle of view that is incident on the first lens group I at the S end largely deviates from the optical axis, and the aberration correction is performed as the lens outer diameter increases. It will be difficult.

According to the present invention, as shown in the paraxial arrangement diagram in FIG. 3B, a fixed diverging lens group is arranged in the first lens group I together with the diaphragm S, so that the first negative lens group at the S end. Due to the diverging action of I, the angle α of the chief ray of maximum field angle incident on the second positive lens group II becomes small (α ₀ > α
₁ ) We were able to eliminate the drawbacks of the positive and negative two-group zoom lens system. Further, since the first lens group I is the negative lens group, the movement of the second positive lens group II and the third positive lens group III, which are the moving groups, effectively contributes to zooming.

[0009]

According to a first aspect of the present invention, a first negative lens group I including at least a positive lens and at least one negative one lens in order from the enlargement side, at least 1
A second lens consisting of one positive lens and at least one negative lens
A positive lens group II, and a third positive lens group III composed of at least one positive lens and at least one negative lens, and a stop S is arranged from the enlargement end to the reduction end of the first negative lens group I, The first negative lens unit I and the diaphragm S are fixed with zooming from the longest focal length end to the shortest focal length end, and the second positive lens unit II and the third positive lens unit III are the second positive lens unit II and the third positive lens unit II. This is a finite-distance zoom lens system characterized by increasing the distance from the positive lens group III and then monotonically moving toward the reduction side while reducing the distance. In the invention according to claim 2 of the present invention, the third positive lens group III includes at least one positive lens from the magnification side, a negative meniscus lens with a convex surface facing the magnification side, a positive lens, and a strong concave surface on the magnification side. The second positive lens group II and the third positive lens group II.
At least one surface of the positive lens group III is composed of an aspherical surface. Further, the invention according to claim 3 of the present invention is characterized in that the surface of the second positive lens group II on the magnifying side of the positive lens is an aspherical surface, and the deviation direction thereof is a direction in which positive power is reduced. .. In the invention according to claim 4 of the present invention, the positive lens on the most magnifying side of the third positive lens group III is a meniscus lens having a convex surface on the magnifying side, and the convex surface is in the direction of reducing positive power and the concave surface is It is characterized by an aspherical surface having a deviation direction in the direction of reducing negative power.

According to a fifth aspect of the present invention, in the third positive lens group III, at least one positive lens is arranged from the magnification side,
A negative meniscus lens with a convex surface facing the magnifying side, a negative lens with a strong concave surface facing the magnifying side, and a positive lens.
At least one of the positive lens group II and the third positive lens group III
The surface is composed of an aspherical surface. In addition, claim 6 of this invention
The described invention is characterized in that the surface of the positive lens of the second positive lens group II on the magnifying side is an aspherical surface, and the deviation direction thereof is a direction in which positive power is reduced. Further, in the invention according to claim 7 of the present invention, the positive lens on the most magnifying side of the third positive lens group III is a meniscus lens having a convex surface directed to the magnifying side, and the convex surface is in the direction of increasing positive power and the concave surface is It is an aspherical surface having a deviation direction in the direction of increasing negative power. According to the eighth aspect of the present invention, the focal length of the first negative lens unit I is f ₁ ,
When the focal length of the second positive lens group II is f ₂ and the focal length of the entire lens system at the longest focal length end is f _L , −1.
_{0 <f 1 / f L <} -0.5,0.7 <f 2 / f L <0.
It is characterized in that each conditional expression 95 is satisfied.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 (A), (B) and 2 (A), (B)
As shown in, the first negative lens group I including a positive lens and at least one negative one lens, and the second positive lens group II including at least one positive lens and at least one negative lens in order from the enlargement side. , A third positive lens group III composed of at least one positive lens and at least one negative lens, the diaphragm S is arranged from the enlargement end to the reduction end of the first negative lens group I, and the longest focal length end The first negative lens unit I and the aperture stop S are fixed, and the second positive lens unit II and the third positive lens unit III are moved to the second position with the zooming toward the shortest focal length end.
The distance between the positive lens group II and the third positive lens group III is increased,
Next, it is a finite-distance zoom lens system characterized by moving monotonically toward the reduction side during reduction.

Furthermore, it is desirable that the third positive lens group III and the second positive lens group II have either of the following two configurations. That is, as shown in FIGS. 1A and 1B, the third positive lens group III has at least one positive lens from the magnification side, a negative meniscus lens having a convex surface facing the magnification side, a positive lens, and a strong magnification side. A negative lens having a concave surface, and a second lens
At least one surface of the positive lens group II and the third positive lens group III is composed of an aspherical surface. (Structure 1)

Alternatively, as shown in FIGS. 2A and 2B, the third positive lens group III includes at least one positive lens from the magnification side, a negative meniscus lens having a convex surface on the magnification side,
It is composed of a negative lens and a positive lens with a strong concave surface facing the magnification side, and at least one surface of the second positive lens group II and the third positive lens group III is an aspherical surface. (Structure 2)

Further, in any of the above-mentioned constitution 1 and constitution 2, the deviation in the positive direction of the axial spherical aberration diverged by the first negative lens unit I, which is fixed together with the diaphragm S, is corrected to the second positive lens unit. II is a combination lens of a positive lens and a negative lens, and the third positive lens group III is arranged as described above to perform the correction. In addition, the second positive lens group II and the third positive lens group II of the off-axis light flux accompanying zooming to the S end
Although the incident point on I becomes high and field curvature and coma aberration occur, the number of lens elements can be reduced by making at least one of the second positive lens group II and the third positive lens group III aspherical. I try to reduce.

Further, in the above-mentioned configurations 1 and 2, off-axis aberrations can be effectively corrected by setting the aspherical shape in the second positive lens group II as follows. That is, the surface on the magnifying side of the positive lens of the second positive lens group II is an aspherical surface, and its deviation direction is set to the direction in which the positive power is reduced.

Further, by setting the aspherical shape of the third positive lens group III as follows, it is possible to effectively correct the off-axis aberration in the above configuration 1. That is, the positive lens closest to the magnification side of the third positive lens group III is a meniscus lens having a convex surface directed toward the magnification side, and the convex surface reduces the positive power, and the concave surface decreases the negative power. It is set to have an aspherical surface.

The positive lens closest to the magnification side of the third positive lens group is a meniscus lens having a convex surface directed toward the magnification side. The convex surface increases the positive power, and the concave surface increases the negative power. Off-axis aberrations can be effectively corrected by setting an aspherical surface having an aberration.

Further, with or without using the configurations 1 and 2, in the configuration of claim 1, the focal length of the first negative lens group I is f ₁ and the second positive lens group II is Let f _{2 be} the focal length of and the focal length of the entire lens system at the longest focal length end (L end) be f _L ,
It is desirable to satisfy the following conditional expression.

-1.0 <f ₁ / f _L <-0.5 ... 0.7 <f ₂ / f _L <0.95 ...

The above-mentioned conditional expression is a condition for securing a variable power range. When the lower limit is exceeded, the second group of movement
The amount of movement of the positive lens group II and the third positive lens group III becomes large, and it becomes impossible to secure the zooming range. If the upper limit is exceeded, the number of constituent lenses of the first negative lens unit must increase.

The above conditional expression is a condition for lowering the incident light flux to the third positive lens group III during zooming to the S end. If the upper limit is exceeded, the height of incidence on the third positive lens group III at the M end (intermediate) and the S end becomes high, making aberration correction difficult. On the other hand, when the value goes below the lower limit, the number of lens components of the second positive lens group II increases.

Next, specific lens configurations of Examples 1 to 6 of the zoom lens system of the present invention are shown in FIGS. 4 to 9, and the numerical values thereof are shown in Table 1, Table 3, Table 5, and Table 7. The results are shown in Table 9 and Table 11. These tables show numerical values on the respective surfaces of the radius of curvature from the expansion side, the axial upper surface distance, the refractive index of the glass material at the d-line, and the Abbe number in order from the top. Further, Table 2, Table 4, Table 6, Table 8, Table 10 and Table 12 show aspherical surface coefficients. These aspherical coefficient tables are given by the following equations when the radius of curvature of the surface apex is C _r0 , the distance from the optical axis is x, the quadric surface parameter is ε, and the aspherical surface coefficients are A ₄ , A ₆ , and A _8. Is defined by

[0023]

[Equation 1]

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

[Table 5]

[0029]

[Table 6]

[0030]

[Table 7]

[0031]

[Table 8]

[0032]

[Table 9]

[0033]

[Table 10]

[0034]

[Table 11]

[0035]

[Table 12]

Table 13 shows the numerical values of the conditional expressions of the respective examples.

[0037]

[Table 13]

Further, FIGS. 10 to 15 show aberration curve diagrams of the spherical aberration, astigmatism, and distortion of Examples 1 to 6, respectively. These aberration curve diagrams are from the top, L end, M end (middle)
And spherical aberration, astigmatism, and distortion at the S edge. It can be seen that the aberrations are satisfactorily corrected in all the examples.

[0039]

As described above, the finite distance zoom lens system of the present invention has an F number of 7.4 and a half angle of view ω = 1.
Although the zoom lens system has a high magnification of 2 ° and a magnification range of −1/20 to −1/50, it is a small lens system with a nine-lens configuration and a small number of lenses. It is a lens system. Moreover, the total length of the prism could be reduced. Further, by using the aspherical surface for the second positive lens group and the third positive lens group, the off-axis aberration can be effectively removed, and the number of lenses can be reduced.

[Brief description of drawings]

1 (A) and 1 (B) show a moving state of a lens group of Configuration 1 of a finite distance zoom lens system of the present invention, and FIG.
Is at the L end, and (B) is at the S end.

2A and 2B show a moving state of a lens group of a finite distance zoom lens system configuration 2 according to the present invention, and FIG.
Is at the L end, and (B) is at the S end.

FIG. 3A is a paraxial layout diagram of a conventional finite distance zoom lens system, and FIG. 3B is a paraxial layout diagram of the finite distance zoom lens system of the present invention;

FIG. 4 is a first embodiment of a finite distance zoom lens system according to the present invention.
Sectional view showing the lens configuration of

FIG. 5 is a second embodiment of the finite distance zoom lens system according to the present invention.
Sectional view showing the lens configuration of

FIG. 6 is a third embodiment of the finite distance zoom lens system according to the present invention.
Sectional view showing the lens configuration of

FIG. 7 is a fourth embodiment of the finite distance zoom lens system according to the present invention.
Sectional view showing the lens configuration of

FIG. 8 is a fifth example of the finite distance zoom lens system according to the present invention.
Sectional view showing the lens configuration of

FIG. 9 is a sixth embodiment of the finite distance zoom lens system according to the present invention.
Sectional view showing the lens configuration of

10 is an L of the finite distance zoom lens system shown in FIG.
Aberration curve diagrams showing spherical aberration, astigmatism, and distortion at the edges, the M edge, and the S edge,

11 is an L of the finite distance zoom lens system shown in FIG.
Aberration curve diagrams showing spherical aberration, astigmatism, and distortion at the edges, the M edge, and the S edge,

12 is an L of the finite distance zoom lens system shown in FIG.
Aberration curve diagrams showing spherical aberration, astigmatism, and distortion at the edges, the M edge, and the S edge,

13 is an L of the finite distance zoom lens system shown in FIG.
Aberration curve diagrams showing spherical aberration, astigmatism, and distortion at the edges, the M edge, and the S edge,

14 is an L of the finite distance zoom lens system shown in FIG.
Aberration curve diagrams showing spherical aberration, astigmatism, and distortion at the edges, the M edge, and the S edge,

FIG. 15 is an L of the finite distance zoom lens system shown in FIG.
Aberration curve diagrams showing spherical aberration, astigmatism, and distortion at the edges, the M edge, and the S edge,

FIG. 16 is an optical path diagram of a microfilm projection optical device.

Claims (8)

[Claims] 1. A first negative lens group I consisting of a positive lens and at least one negative one lens, and a second positive lens group II consisting of at least one positive lens and at least one negative lens in order from the enlargement side. , A third positive lens group III composed of at least one positive lens and at least one negative lens, the diaphragm S is arranged from the enlargement end to the reduction end of the first negative lens group I, and the longest focal length end The first negative lens unit I and the aperture stop S are fixed, and the second positive lens unit II and the third positive lens unit III are moved to the second position with the zooming toward the shortest focal length end.
The distance between the positive lens group II and the third positive lens group III is increased,
Next, a finite-distance zoom lens system characterized by moving monotonically toward the reduction side during reduction. 2. The third positive lens group III is composed of at least one positive lens from the magnification side, a negative meniscus lens having a convex surface facing the magnification side, a positive lens, and a negative lens having a strong concave surface facing the magnification side. , The second positive lens group II and the third positive lens group
At least one surface of III is composed of an aspherical surface.
Finite distance zoom lens system described. 3. The finite distance zoom according to claim 2, wherein the surface of the positive lens of the second positive lens group II on the magnifying side is an aspherical surface, and the direction of deviation is a direction in which positive power is reduced. Lens system. 4. The positive lens closest to the magnification side of the third positive lens group III is a meniscus lens having a convex surface directed toward the magnification side, and the convex surface diviates in the direction of reducing positive power and the concave surface diviates in the direction of reducing negative power. The finite distance zoom lens system according to claim 2, wherein the finite distance zoom lens system is an aspherical surface having an azimuth direction. 5. The third positive lens group III comprises at least one positive lens from the magnification side, a negative meniscus lens having a convex surface facing the magnification side, a negative lens having a strong concave surface facing the magnification side, and a positive lens, Second positive lens group II and third positive lens group II
The finite distance zoom lens system according to claim 1, wherein at least one surface of I is composed of an aspherical surface. 6. The finite distance zoom according to claim 5, wherein the surface of the positive lens of the second positive lens group II on the magnifying side is an aspherical surface, and the direction of deviation is a direction in which positive power is reduced. Lens system. 7. The positive lens closest to the magnification side of the third positive lens group III is a meniscus lens having a convex surface directed toward the magnification side, and the convex surface is divided in a direction increasing positive power and the concave surface is divided in a direction increasing negative power. The finite distance zoom lens system according to claim 5, wherein the finite distance zoom lens system is an aspherical surface having an azimuth direction. 8. When the focal length of the first negative lens group I is f ₁ , the focal length of the second positive lens group II is f ₂ and the focal length of the entire lens system at the longest focal length end is f _L , The finite distance zoom lens system according to claim 1, wherein the following conditional expression is satisfied. _{-1.0 <f 1 / f L <} -0.5 ···· 0.7 <f 2 / f L <0.95 ···