JPH05119259A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain the zoom lens of seven-element constitution which has an about 60 field angle and is variable in power by satisfying specific expressions. CONSTITUTION:A 1st-a 4th lens are arranged in order from the object side and a 5th-a 7th lens which are finished in a shape of mirror surface symmetry with the 3rd, 2nd, and 1st lens about the 4th lens are arranged in order on the image side about the 4th lens. The 1st lens is a negative lens which has a concave surface on the image side and the 2nd lens is a meniscus lens which is concave to the image side; and the 3rd lens is a meniscus lens which is concave to an image plane and the 4th lens is a biconvex lens. Those 1st-4th lenses satisfy the inequalities I-IV. Here, f1 is the focal length of the 1st lens, T the distance between object images of the whole system, nu1 the Abbe number of the 1st lens glass material, r3 the radius of curvature of the surface of the 2nd lens which faces a body, L the distance from the object-side surface of the 2nd lens to the 4th lens, and f4 the focal length of the 4th lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens used in a plate making camera, a copying machine or the like, and more particularly to a zoom lens having a photographing magnification including equal magnification.

[0002]

2. Description of the Related Art As a zoom lens for a plate making camera and a copying machine, which can be magnified under the condition that the object-image distance is constant, for example, JP-A-48-49453 and JP-A-5-49453 are known.
The ones disclosed in JP-A-5-11260, JP-A-60-209714 and JP-A-1-145617 are conventionally known.

Table 1 summarizes the specifications of the zoom lenses described in these publications.

[0004]

[Table 1]

As can be seen from the table, the widest angle of view of these zoom lenses is 50 °, and the others are less than 40 °. A zoom lens having an angle of view of 50 ° is composed of 12 lenses. Further, even if the zoom lens has the smallest number of lenses, eight lenses are used.

[0006]

By the way, from the viewpoint of miniaturizing a plate-making camera and a copying machine using a zoom lens, an area defined by the specifications of the apparatus can be photographed with the object-image distance as small as possible. Is desirable.
That is, the wider the angle of view of the zoom lens, the better. However, conventionally, the angle of view of a zoom lens is only 50 °.

In addition, there are the following problems. That is, in order to reduce the apparatus cost, it is advantageous that the number of constituent lenses of the zoom lens is small. However,
As described above, in the conventional zoom lens, even if the angle of view is 50 °, the number of constituent lenses of the zoom lens is 12, which increases the cost of the apparatus. On the other hand, there are some lenses having about eight lenses, but in this case, there is a drawback that the angle of view is narrow.

As described above, the conventional zoom lens has a problem that the angle of view is narrow and the number of lenses is large.

The present invention has been made in order to solve the above problems, and an object thereof is to provide a zoom lens having a seven-lens structure having an angle of view of about 60 ° and capable of changing a photographing magnification. To do.

[0010]

According to the present invention, first to fourth lenses are sequentially arranged from the object side, and the third lens, the second lens and the first lens are mirror-symmetrical with respect to the fourth lens. The fifth to seventh lenses finished as described above are sequentially arranged on the image side with respect to the fourth lens.
A zoom lens capable of changing the focal length of the entire system by changing the distance between the lens and the second lens and the distance between the sixth lens and the seventh lens, in order to achieve the above object, The first lens is a negative lens having a concave surface on the image side, the second lens is a meniscus lens having a concave surface facing the image side, and the third lens is a meniscus lens having a concave surface facing the image side. , The fourth lens is a biconvex lens, and the following inequality

[0011]

[Equation 5]

[0012]

[Equation 6]

[0013]

[Equation 7]

[0014]

[Equation 8]

Where f1 is the focal length of the first lens,
T is the distance between object images of the entire system, ν1 is the Abbe number of the first lens glass material, r3 is the radius of curvature of the surface of the second lens facing the object side,
L is the distance from the surface of the second lens facing the object side to the fourth lens, and f4 is the focal length of the fourth lens.

[0016]

## EQU5 ## Formula 5 defines the range of the focal length of the first lens. When the value goes below the lower limit of Expression 5, the power of the first lens becomes weak, and the change in the distance between the first lens and the second lens due to zooming increases. In this way, when the interval change becomes large,
The size of the first lens becomes large, the lens barrel becomes long, and the cost increases. On the other hand, if the upper limit of Expression 5 is exceeded, the power of the first lens becomes strong, and it becomes difficult to correct astigmatism.

Equation 6 is a condition for reducing the chromatic dispersion of the first lens. Since the first lens is moved by a single lens, unless the chromatic aberration of the single lens is small to a certain extent, the chromatic aberration of the entire system will largely change with zooming.

Equation 7 is a condition for the center of curvature of the surface of the second lens facing the object side to substantially coincide with the center position of the fourth lens which also functions as a diaphragm. If this condition (Equation 7) is not satisfied, the generation of astigmatism on this surface will increase.

Equation 8 defines the power range of the fourth lens. The function of the fourth lens is to focus the light flux. Therefore, if the power of the fourth lens is too weak, the object-image distance becomes large, whereas if it is too strong, the aberration balance with other lenses is lost.

[0020]

【Example】

A. First Example FIG. 1 is a diagram showing a first example of the zoom lens according to the present invention. In addition, in the first example and all the examples described in detail later, the e-line (546 nm) is used as the main wavelength in accordance with the sensitivity range of an ortho film often used for plate making,
Besides, in consideration of the F line (486 nm) and the g line (436 nm), the structure is as follows.

This zoom lens, as shown in FIG.
It is composed of first to seventh lenses 1 to 7. The first to fourth lenses 1 to 4 are arranged in this order from the object side (left hand in the figure), while the fifth to seventh lenses 5 to 7 are arranged.
Are arranged in this order on the image side (right hand in the figure) with respect to the fourth lens 4 whose lens frame (not shown) functions as a diaphragm. Further, the fifth to seventh lenses 5 to 7 are
For the fourth lens 4, the third, second and first lenses 3, 2,
It is finished in mirror-symmetrical shape with No. 1 respectively. In addition, in the first embodiment, the second and third lenses 2 and 3 are cemented together, and the fifth and sixth lenses 5 and 6 are also cemented together. The above is indicated in the lens data described in the table described later.

The first and seventh lenses 1 and 7 are reciprocally movable in the optical axis direction Z by a lens driving mechanism (not shown). Therefore, the first and seventh lenses 1 and 7 are moved in the optical axis direction Z so that the distance d2 between the first lens 1 and the second lens 2 and the distance d between the sixth lens 6 and the seventh lens 7 are increased.
It is possible to change 10 respectively, and thereby it is possible to change the focal length of the entire zoom lens system.

Tables 2 and 3 are tables showing lens data of the zoom lens according to the first embodiment.

[0024]

[Table 2]

[0025]

[Table 3]

In these tables (and Tables 4 to 9 described later), the respective symbols are defined as follows. That is, ri is the radius of curvature of the i-th lens surface counted from the object side, d0 is the distance from the object to the first lens 1, di (where i = 1-11) is counted from the object side. Between the i-th lens surface and the (i + 1) -th lens surface on the optical axis, d12 ... Distance between seventh lens 7 and image surface, nd ... First to seventh, respectively The refractive indices of the lenses 1 to 7 with respect to the d-line, vd ... Abbe numbers of the first to seventh lenses 1 to 7 with respect to the d-line, .beta.

In the first embodiment, the object-to-image distance T, the F-number FNO at the same magnification, the diaphragm diameter (the diameter of the lens frame of the fourth lens 4) φ and the angle of view 2θ are T = 1000, FNO. = 12.5, φ = 14.2, 2θ = 60 °.

When the magnification is 1/3, 1 or 3 times, the effective F-numbers F1 / 3, F1 and F3 at the respective magnifications are set.
Is F1 / 3 = 12.9, F1 = 25, F3 = 38.5, and the document sizes .phi.1 / 3, .phi.1, .phi.3 at each magnification.
Are φ1 / 3 = 825, φ1 = 558, and φ3 = 255.

From the above data, the distance L from the surface of the second lens 2 facing the object side to the diaphragm (lens frame of the fourth lens 4) is L = (d3 + d4 + d5 + d6 / 2) = 58. It becomes 261. Therefore, the values (f1 / T), ν1, (r3 /
L) and (f4 / T) are f1 / T = -0.27, ν1 = 64.1, r3 / L = 0.90, f4 / T = 0.54, and the zoom lens according to the first example. It is clear that the above equations satisfy the equations 5 to 8, respectively.

2 to 4, the photographing magnification is 1 respectively.
9 shows various aberrations of the zoom lens according to the first example when the magnification is / 3 times, 1 time, and 3 times. In each of the drawings (and FIGS. 6 to 8, FIGS. 10 to 12, and 14 to 16 described later), reference numerals e, F, and g denote the e line (546 nm) and the F line (4 nm), respectively.
86 nm) and g line (436 nm) are shown.
The solid line S indicates the sagittal image plane, and the broken line M indicates the meridional image plane.

B. Second Example FIG. 5 is a diagram showing a second example of the zoom lens according to the present invention. Since the configuration of this zoom lens is the same as that of the first embodiment, its description is omitted. Table 4 and Table 5
6 is a table showing lens data of the zoom lens according to the second example.

[0032]

[Table 4]

[0033]

[Table 5]

In the second embodiment, the object-image distance T, the F-number FNO at the same magnification, the aperture diameter φ and the angle of view 2θ are T = 1000, FNO = 12.5, φ = 15.3, 2θ = 60 °.

When the magnification is 1/3, 1 or 3 times, the effective F-numbers F1 / 3, F1 and F3 at the respective magnifications are set.
Is F1 / 3 = 12.9, F1 = 25, F3 = 38.5, and the document sizes .phi.1 / 3, .phi.1, .phi.3 at each magnification.
Are φ1 / 3 = 811, φ1 = 548, and φ3 = 249.

From the above data, the distance L from the surface of the second lens 2 facing the object side to the stop (lens frame of the fourth lens 4) is L = (d3 + d4 + d5 + d6 / 2) = 59. It becomes 194. Therefore, the values (f1 / T), ν1, (r3 /
L) and (f4 / T) are f1 / T = -0.25, ν1 = 95, r3 / L = 0.94, f4 / T = 0.59, and the number of zoom lenses according to the second embodiment is several. It is clear that each of 5 to 8 is satisfied.

6 to 8, the photographing magnification is 1 respectively.
9 shows various aberrations of the zoom lens according to the second example when the magnification is / 3 times, 1 time, and 3 times.

By the way, in the second embodiment, the first and seventh lenses 1 and 7 are made of a glass material having a refractive index nd and an Abbe number νd of nd = 1.43425 and νd = 95. This glass material has been developed in recent years and has a characteristic of extremely small color dispersion. As described above, when the first and seventh lenses 1 and 7 that move by a single lens are formed of this glass material, Good results are obtained. This can be easily understood by comparing, for example, FIG. 3 (a) and FIG. 7 (a). That is, in the first embodiment, the first and seventh lenses 1 and 7 are made of a normal glass material (nd = 1.51633, νd = 64.1), and as shown in FIG. While the chromatic aberration of the g-line is about 6 mm, the glass material (n
Since d = 1.43425, νd = 95), it is about 3 mm, which is half that of the first embodiment.

C. Third Embodiment FIG. 9 is a diagram showing a third embodiment of the zoom lens according to the present invention. As shown in the figure, this zoom lens has a seven-lens structure as in the first embodiment (FIG. 1), but the second and third lenses 2 and 3 are separated from each other, and the fifth and sixth lenses are separated. 5 and 6 are also separated from each other, which is a big difference from the first embodiment. The zoom lens according to Example 4 described later is also the same as in Example 3.

Tables 6 and 7 are tables showing lens data of the zoom lens according to the third embodiment.

[0041]

[Table 6]

[0042]

[Table 7]

In the third embodiment, the object-image distance T, the F-number FNO at the same magnification, the aperture diameter φ and the angle of view 2θ are T = 1000, FNO = 12.5, φ = 16.3, 2θ = 60 °.

When the magnification is 1/3, 1 or 3 times, the effective F-numbers F1 / 3, F1 and F3 at the respective magnifications are set.
Is F1 / 3 = 13.1, F1 = 25, F3 = 39.5, and the document sizes φ1 / 3, φ1, φ3 at each magnification.
Are φ1 / 3 = 833, φ1 = 565, and φ3 = 261.

From the above data, the distance L from the surface of the second lens 2 facing the object side to the diaphragm (lens frame of the fourth lens 4) is L = (d3 + d4 + d5 + d6 / 2) = 54. It becomes 605. Therefore, the values (f1 / T), ν1, (r3 /
L) and (f4 / T) are f1 / T = -0.33, ν1 = 90.3, r3 / L = 1.12, f4 / T = 0.48, and the zoom lens according to the third example. It is clear that the above equations satisfy the equations 5 to 8, respectively.

FIGS. 10 to 12 show various aberrations of the zoom lens according to the third example when the photographing magnifications are 1/3, 1 and 3, respectively.

D. Fourth Example FIG. 13 is a diagram showing a fourth example of the zoom lens according to the present invention. Tables 8 and 9 are tables showing lens data of the zoom lens according to the fourth example.

[0048]

[Table 8]

[0049]

[Table 9]

In the fourth embodiment, the object-to-image distance T, the F-number FNO at the same magnification, the diaphragm diameter φ and the angle of view 2θ are T = 1000, FNO = 12.5, φ = 15.5, 2θ = 60 °.

When the magnification is 1/3, 1 or 3 times, the effective F-numbers F1 / 3, F1 and F3 at the respective magnifications are set.
Is F1 / 3 = 13.1, F1 = 25, F3 = 39.5, and the document sizes φ1 / 3, φ1, φ3 at each magnification.
Are φ1 / 3 = 838, φ1 = 566, and φ3 = 261.

From the above data, the distance L from the surface of the second lens 2 facing the object side to the diaphragm (lens frame of the fourth lens 4) is L = (d3 + d4 + d5 + d6 / 2) = 61. It becomes 07. Therefore, the values (f1 / T), ν1, (r3 /
L) and (f4 / T) are f1 / T = -0.32, ν1 = 64.1, r3 / L = 1.01 and f4 / T = 0.43, and the zoom lens according to the fourth embodiment. It is clear that the above equations satisfy the equations 5 to 8, respectively.

FIGS. 14 to 16 show various aberrations of the zoom lens according to the fourth example when the photographing magnifications are 1/3, 1 and 3 respectively.

[0054]

As described above, according to the present invention, it is possible to obtain a zoom lens having seven lenses and an angle of view of 60 °. Therefore, it is possible to shoot with a relatively small object-image distance compared to the shooting region, and it is possible to make the device including the zoom lens compact and further reduce the device cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a lens configuration when a magnification is 1/3 in a first embodiment of a zoom lens according to the present invention.

FIG. 2 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is 1/3 in the first example.

FIG. 3 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is 1 in the first example.

FIG. 4 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is 3 × in the first example.

FIG. 5 is a configuration diagram showing a lens configuration when the magnification is ⅓ in the second example of the zoom lens according to the present invention.

FIG. 6 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is 1/3 in the second example.

FIG. 7 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is 1 in the second example.

FIG. 8 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is 3 × in the second example.

FIG. 9 is a configuration diagram showing a lens configuration when the magnification is ⅓ in the third example of the zoom lens according to the present invention.

FIG. 10 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is 1/3 in the third example.

FIG. 11 is a diagram showing spherical aberration, astigmatism, and distortion when the magnification is 1 in Example 3;

FIG. 12 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is 3 × in the third example.

FIG. 13 is a configuration diagram showing a lens configuration when the magnification is ⅓ in the fourth example of the zoom lens according to the present invention.

FIG. 14 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is ⅓ in the fourth example.

FIG. 15 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is 1 in Example 4.

FIG. 16 is a diagram showing spherical aberration, astigmatism, and distortion when the imaging magnification is 3 × in the fourth example.

[Explanation of symbols]

 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens 6 6th lens 7 7th lens

Claims (1)

[Claims] 1. The first to fourth lenses are sequentially arranged from the object side, while the fifth to fifth finished mirror-symmetrical to the third, second and first lenses with respect to the fourth lens. Seven lenses are sequentially arranged on the image side with respect to the fourth lens, and the entire system is changed by changing the distance between the first lens and the second lens and the distance between the sixth lens and the seventh lens. A zoom lens capable of changing the focal length of the first lens, the first lens is a negative lens having a concave surface on the image side, the second lens is a meniscus lens having a concave surface on the image side, The lens is a meniscus lens with a concave surface facing the image side, the fourth lens is a biconvex lens, and the following inequality: [Equation 2] [Equation 3] [Equation 4] Where f1 is the focal length of the first lens, T is the object-to-image distance of the entire system, ν1 is the Abbe number of the first lens glass material, r3 is the radius of curvature of the surface of the second lens facing the object side, and L is the Distance from the surface of the two lenses facing the object side to the fourth lens, f4
Is a zoom lens characterized by satisfying the focal length of the fourth lens.