JP2739649B2 - Zoom lens for variable magnification copier - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens for a variable magnification copier, and more particularly, to a conjugate length (object-image distance) from an object plane to an imaging plane. The present invention relates to a zoom lens suitable for zooming while maintaining a constant value.

[Conventional technology]

With the advent of copiers, especially electrophotographic copiers using plain paper, extremely efficient business operations can be performed. However, in recent years, with the diversification of needs for copiers, a function for obtaining a hard copy with the above dimensional ratio changed, that is, a scaling function for obtaining an enlarged copy or a reduced copy. It has come to be strongly required to provide.

In this case, there are various types of zooming functions, one example of which performs zooming using an equal-magnification lens. Specific means in this example include changing the distance from the fixed focal length lens to the object plane and the distance from the lens to the image forming plane, that is, changing the conjugate length (distance between object images), In some cases, a converter lens is inserted in the optical path of the fixed focal length lens at the time of reduction.

In the case of performing magnification by changing the former conjugate length, it is necessary to move a folding mirror or the like in order to change the conjugate length. The magnification increases over a wide range, for example, from about 0.5 to 2.0 times, so that the amount of movement of the folding mirror and the like becomes very large, and the entire optical system becomes large. In addition to the drawbacks, there are problems that the number of components increases and that special high precision members are required.

In addition, in the case of performing the magnification change by interposing the latter converter lens, it is needless to say that only one magnification ratio can be changed by one converter lens. To A4 size,
If the scaling size is specified due to gradual scaling by preparing multiple converter lenses for reducing A3 size to A4 size, etc., for example, unified storage of copy size Etc., but cannot fully meet the needs of the user. In addition, since these converter lenses are composed of at least two lenses, the cost is high. Must be prepared for multiple scaling factors,
Since these switching mechanisms are also complicated, there is a problem that the overall cost is increased.

For this reason, zoom lenses have been developed for changing the magnification while keeping the conjugate length from the object plane to the image plane constant. An example of such a zoom lens is disclosed in
There is one described in 151604.

In other words, the optical system arranges the same lens group as the “concave lens, convex lens, concave lens” symmetrically on the object plane side and the image plane side with the stop as the center. The second lens group includes a fixed lens group including a first lens and a sixth lens, a first movable lens group including a second lens and a third lens, and a fourth lens group. It is composed of a total of four lens groups including a second moving lens group consisting of a fifth lens.

When the magnification is the same, the first to sixth lenses are positioned so as to be symmetrical with respect to the object plane side and the image plane side with respect to the stop. Enlargement and reduction are performed by moving the apertures by an equal amount about the stop.

[Problems to be solved by the invention]

However, the zoom optical system described in Japanese Patent Application Laid-Open No. 61-151604 performs zooming by moving the moving group symmetrically around the stop, with the F No. being as dark as about 11. Therefore, the zoom lens had a drawback that the zoom range was 0.647 to 1.414 times, which was narrower.

Further, when the magnification is near the same magnification, the moving amount of each lens group is small, and the moving distance increases as the magnification moves away from the same magnification (magnification side or reduction side).
The amount of movement increases sharply from around 4 times (0.707 times at the time of reduction), so that the movement of each group is moved symmetrically around the aperture, and the range of the magnification ratio from 0.5 times to 2 times is increased. In order to achieve this, the distance between each group must be kept large, and the overall length of the lens becomes extremely long. At the time of zooming, various imaging performances especially at magnifications apart from the same magnification are significantly deteriorated. was there.

The present invention has been made in view of the above-mentioned problems of the related art, and an object of the present invention is to maintain the conjugate length from the object plane to the image plane constant while maintaining the conjugate length from about 0.5 to 2.0. It is an object of the present invention to provide a zoom lens for a variable magnification copying machine which can provide a variable magnification over a wide range of about 2 times with a small number of lens components and does not cause an increase in size or deterioration of image quality.

[Means for solving the problem]

In order to achieve the above object, the present invention provides, in order from an object plane to an image plane, a first lens composed of a meniscus concave lens whose concave surface faces the object side, a second lens composed of a convex lens, and a second lens composed of a convex lens. A third lens composed of a meniscus concave lens having a concave surface, a diaphragm, a fourth lens composed of the same lens as the third lens and having a concave surface facing the image surface side, and a third lens composed of the same lens as the second lens. A zoom lens for a variable magnification copying machine having a six-group, six-element configuration, in which five lenses and a sixth lens having the same lens as the first lens and having a concave surface facing the image plane are arranged. When forming an image on the image plane at the same magnification, the first to sixth lenses are arranged symmetrically with respect to the stop, the focal length of the first lens is f1, and the focal length of the second lens is f2. If the combined focal length of the entire lens system at the same magnification is f0 To 0.6 <| f1 / f0 | at <0.7 and 0.35 <| f2 / f0 | satisfies the condition of <0.43, when to scale the object plane is imaged on an image plane, said first
By moving at least the first lens and the sixth lens out of the sixth lens and the diaphragm asymmetrically and moving the entire lens system in the optical axis direction, the conjugate length from the object plane to the image plane can be made equal. The feature is that continuous zooming is possible while keeping the zoom constant regardless of zooming.

(Operation)

The second, third, fourth, and fifth lenses in the zoom lens for a variable magnification copying machine according to the present invention configured as described above mainly function as aberration correction lenses as master lenses, while the first, third, and fourth lenses function as master lenses. The sixth series is effectively added to the outside of the master lens to reduce the amount of movement of the lens during zooming.

When coupling to the image plane at the same magnification, six lenses in six groups are arranged symmetrically with respect to the stop. On the other hand, when performing magnification, the first and second lenses added to the outside of the master lens are used. By moving the six lenses and part or all of the master lens, the focal length is changed,
By moving the entire lens in the optical axis direction, zooming is performed with the conjugate length fixed.

At this time, by moving each lens group asymmetrically around the stop, it is possible to avoid an increase in the amount of movement of the lens particularly at a magnification apart from the same magnification, and to suppress the deterioration of the imaging performance.

Further, in the above-described configuration and the manner of movement of each lens, the focal length f1 (or f1) of the first (or sixth) lens with respect to the focal length f0 of the focusing system of the entire lens system at the same magnification.
6) and the relationship between the focal length f2 (or f5) of the second (or fifth) lens is defined by the following conditions: 0.6 <| f1 / f0 | <0.7 and 0.35 <| f2 / f0 | <0.43. The power arrangement of the first (sixth) lens and the second (or fifth) lens of the master lens is determined to achieve further compactness and improvement of the imaging performance.

By keeping the upper limit of | f1 / f0 | at 0.7, the moving amount of the moving lens during zooming is prevented from becoming large, and the entire lens system is made compact. Is set to 0.6 to prevent the occurrence of large aberrations that tend to occur in the first lens and the sixth lens.

Furthermore, the upper and lower limits of | f2 / f0 |
0,35, Petzval sum too large,
The MTF is prevented from becoming too small, and the astigmatic difference and the curvature of field are suppressed as much as possible to prevent the MTF from deteriorating.

〔Example〕

Hereinafter, embodiments of a zoom lens for a variable magnification copying machine according to the present invention will be described in detail with reference to the accompanying drawings.

First, a first embodiment of the present invention will be described with reference to FIGS.
(C), FIGS. 3 (A1) to (A3), FIGS. 3 (B1) to (B)
3), FIGS. 3 (C1)-(C3) and FIGS. 4 (A)-
This will be described with reference to FIG.

FIG. 1 is a lens configuration diagram showing a basic configuration of a zoom lens, in which an object surface side, for example, a document surface in an electrophotographic copying machine, and an image surface side, for example, an exposure surface of an image carrier such as a photosensitive drum. And a zoom lens is interposed between them. This zoom lens includes first to third lenses L1 to L3, an aperture a, and fourth to sixth lenses in order from the object plane to the image plane.
Lenses L4 to L6 are arranged. That is, the first lens L1
Is a meniscus concave lens (negative meniscus lens) formed of a concave surface of the surface 1 located on the object side and a convex surface of the surface 2 located on the image surface side, with the concave surface facing the object side, and the second lens L2
Is a convex lens (biconvex lens) formed by the convex surface of the surface 3 and the convex surface of the surface 4, and the third lens L3 is a meniscus concave lens formed by the concave surface of the surface 5 and the convex surface of the surface 6 and having the concave surface facing the object side. A stop a located on the surface 7 is arranged on the image plane side of the third lens L3. On the image side of the aperture a,
A fourth lens L4, which is a meniscus concave lens having a convex surface facing the object side and formed by a convex surface of the surface 8 that is the same as the surface 6 and a concave surface of the surface 9 that is the same as the surface 5, is arranged. On the image plane side of the fourth lens L4, a fifth convex lens (surface convex lens) formed by a convex surface of the surface 10 identical to the surface 4 and a convex surface of the surface 11 identical to the surface 3 is provided. lens
L5 is located. On the image plane side of the fifth lens L5,
A sixth lens L6, which is a meniscus concave lens having a concave surface facing the image surface side and formed by a convex surface of the surface 12 that is the same as the surface 2 and a concave surface of the surface 13 that is the same as the surface 1, is disposed. .

In addition, the radii of curvature r1 to r13 of the surfaces 1 to 13 forming the first to sixth lenses L1 to L6, and the surfaces 1 to 13
Distance d1 to d12, refractive index N1 to N6, and Abbe number ν1
Are set as shown in Table 1 below.

Here, in the above-mentioned first to sixth lenses L1 to L6, the focal length of the first lens L1 is f1, the focal length of the second lens L2 is f2, and the combined focal length of the entire lens system at the same magnification is set. When the distance is f0, 0.6 <| f1 / f0 | <0.7 and 0.35 <| f2 / f0 | <0.43 are satisfied. That is, the respective values of f1, f2, f0 are f1 = −129.500 f2 = 78.573 f0 = 200.0, and therefore the value of | f1 / f0 | is 0.647 and the value of | f2 / f0 | is 0.393. .

Note that each of the “first lens L1 and sixth lens L6” and the “second lens L2 and fifth lens L5” are exactly the same lens (but in opposite directions), so the focal length of the sixth lens L6 When f6 and the focal length f5 of the fifth lens L5 are satisfied, naturally, the following conditions are satisfied: 0.6 <| f6 / f0 | <0.7 and 0.35 <| f5 / f0 | <0.43. As a result, | f1 / f0 | = | f6 / f0 | and | f2 / f0 | = | f5 / f0 |.

Now, the above-mentioned 0.6 <| f1 / f0 | <0.7 or 0.6 <| f6 / f0 |
The condition of <0.7 determines the power of the first lens L1 and the sixth lens L6. When the value of | f1 / f0 | = | f6 / f0 | The movement amount becomes large,
The entire lens system cannot be made compact.

If the value of | f1 / f0 | = | f6 / f0 | is less than the lower limit of 0.6, very large aberrations occur in the first lens L1 and the sixth lens L6. Is the first lens
It is necessary to increase the number of components of the lens L1 and the sixth lens L6, which leads to an increase in cost and a reduction in the size of the entire lens system.

On the other hand, the aforementioned 0.35 <| f2 / f0 | <0.43 or 0.35 <| f5 / f
The condition 0 | <0.43 determines the power arrangement of the master lens formed by the second lens L2 and the fifth lens L5.
If the value of | f2 / f0 | = | f5 / f0 | exceeds the upper limit of 0.43, the Petzval sum increases, the image plane shifts in the negative direction, and astigmatism (aberration) increases.

If the value of | f2 / f0 | = | f5 / f0 | is smaller than the lower limit of 0.35, the Petzval sum becomes smaller, the image plane shifts in the positive direction, and the field curvature increases.

Further, when the value of | f2 / f0 | = | f5 / f0 | exceeds the above upper limit value or falls below the lower limit value, the on-axis and off-axis balances are disrupted, causing deterioration of the MTF.

The axial distances d2, d4, d6, d7, in FIG.
d9 and d11 have different values at the same magnification and at the time of zooming. In other words, the first to sixth lenses L1 to L6 move as shown in Table 2.

As shown in Table 1, the zoom lens formed by the first to sixth lenses L1 to L6 and the like in which each part is set has a lens configuration diagram at the time of enlargement (m = 2.0) in FIG. FIG. 2 (B) shows a lens configuration diagram at the same magnification (m = 1.0).
FIG. 2C shows a lens configuration at the time of reduction (m = 0.5).

In this case, the third lens L3 is fixed during zooming between the same magnification and reduction, while the fourth lens L4 is fixed during zooming between the same magnification and magnification. I have. Here, paying attention to the axial distance d2 between the first lens L1 and the second lens L2, the time from the enlargement (m = 2.0) to the reduction (m = 0.5) through the same magnification (m = 1.0). In the meantime, it will change from 4.851 to 3.403 via 0.5.

On the other hand, focusing on the on-axis distance d11 between the sixth lens L6 and the fifth lens L5, the time of reduction (m = 0.5) from the time of enlargement (m = 2.0) to the same time (m = 1.0) Between 3.403
From 0.5 to 4.851.

As is clear from the comparison between the two, when the magnification is equal (m =
1.0), the first lens L1 and the sixth lens
It can be seen that each of the lenses L6 moves in the opposite direction and the amount of movement is the same.

On the other hand, the relationship between the movement of the second lens L2 and the third lens L3 and the movement of the fourth lens L4 and the fifth lens L5 (the relationship between the axial distance d4 and the axial distance d9) is the same as described above. The same can be said for the relationship between the on-axis interval d6 and the on-axis interval d7. Therefore, when the object plane is imaged on the image plane at the same magnification, the first to sixth lenses L1 to L6 are connected to the aperture a
The first lens L1 to the sixth lens are arranged symmetrically with respect to
This means that L6 is moved by a symmetric value with respect to the amount of movement at the time of enlargement and the amount of movement at the time of reduction.

Naturally, the entire lens system is appropriately moved in the optical axis direction between the object plane and the image plane with the zoom movement of the zoom lens, so that the conjugate from the object plane to the image plane can be obtained. It is possible to continuously change the magnification while keeping the length constant regardless of the magnification and the magnification.

D-line (587.56 nm) corresponding to the lens configuration diagram of the first embodiment at the time of magnification, at the same magnification, and at the time of reduction, respectively shown in FIGS. 2 (A), (B) and (C);
FIGS. 3 (A1), (B1) and (C1) show spherical aberration diagrams of the F-line (486.13 nm) and the C-line (656.27 nm), and show the d-line of each of the sagittal ray and the meridional ray.
Fig. 3 (A2) shows the astigmatism of the F line and the C line.
(B2) and (C2), and distortion diagrams of distortion are shown in FIGS. 3 (A3), (B3) and (C3), respectively.

Similarly, for coma, d-line, F-line,
FIG. 4 (A) shows the aberration diagram when each of the C lines is enlarged (m = 2.0), and FIG. 4 (B) shows the aberration diagram when the same magnification (m = 1.0). The aberration diagrams at (m = 0.5) are shown in FIG. 4 (C), respectively.
However, the characteristics of 74.25 at the time of enlargement, 148.5 at the same time and 148.5 at the time of reduction,
The characteristics of 0.9Y, 0.75Y, 0.5Y, 0.25Y and the respective on-axis characteristics are shown.

In the aberration diagrams shown in FIGS. 3 (A1), (B1) and (C1), SA represents spherical aberration, SC represents a sine condition, and the spherical aberration is represented by a solid line and the sine condition is represented by a broken line. Are indicated respectively.

In the aberration diagrams shown in FIGS. 3 (A2), (B2) and (C2),
DS and DM represent astigmatism, of which sagittal rays are indicated by solid lines and meridional rays are indicated by broken lines.

In the aberration diagrams shown in FIG. 3 (A3), (B3) and (C3),
DIST indicates distortion.

As is clear from the above aberration diagrams, the on-axis and off-axis balances are very well-balanced at each magnification, and the coma aberration shows that although the aperture efficiency is almost 100%, the flare It can be seen that the components are very small and are well corrected.

Although the spatial frequency vs. MTF characteristic curve is not shown, the MTF characteristic has a very high contrast not only at the same magnification but also at the time of enlargement and reduction, and thus is finally obtained. The image quality of the hard copy can be significantly improved.

Next, FIGS. 5 (A), (B) and (C) and FIGS. 6 (A1) to 6 (A1) to (C1) show the second embodiment of the present invention for each state of enlargement, equal magnification and reduction. A3), Fig. 6 (B1)-(B3)
This will be described with reference to FIGS. 6 (C1) to 6 (C3) and FIGS. 7 (A), 7 (B) and 7 (C). In this embodiment, each part of the first to sixth lenses L1 to L6 is configured as shown in Table 3 below.

Further, the axial distances d2, d4, d9, d11 in the first lens L1 to the sixth lens L6 in which the respective parts are set as shown in Table 3
Is changed as shown in Table 4 below according to each magnification.

The zoom lens formed by the first to sixth lenses L1 to L6 and the like in which each part is set as shown in Tables 3 and 4 has a lens configuration at the time of enlargement (m = 2.0). Figure (A)
FIG. 5 (B) shows a lens configuration at the time of equal magnification (m = 1.0), and FIG. 5 (C) shows a lens configuration at the time of reduction (m = 0.5).

In this embodiment as well, the conjugate length from the object plane to the image plane is kept constant irrespective of the same magnification and the same magnification as in the first embodiment described above. A zoom lens is obtained.

In the second embodiment, the axial distance d6 between the surface 6 forming the third lens L3 and the stop a, the fourth lens
The line spacing d7 between the surface 8 forming L4 and the stop a is 0.30
It is fixed at 0. Therefore, the zoom movement is performed by the first lens L1, the second lens L2, the fifth lens L5, and the sixth lens L6.
Is performed by moving only the third lens L3 and the fourth lens
L4 is a fixed lens group.

Further, the spherical aberration corresponding to the lens configuration diagram at the time of enlargement, at the same magnification, and at the time of reduction of the second embodiment shown in each of FIGS. The aberration diagrams are shown in FIGS. 6 (A1), (B1) and (C1), the astigmatism aberration diagrams are shown in FIGS. 6 (A2), (B2) and (C2), and the distortion aberration diagrams are shown. Fig. 6 (A3), (B
See 3) and (C3).

Similarly, regarding coma aberration, FIG.
(B) and (C).

Next, FIGS. 8 (A), (B) and (C) and FIGS. 9 (A1) to 9 (A1) to 9 (A1) to (C) show the third embodiment of the present invention for each of the states at the time of enlargement, equal magnification and reduction. A3), Fig. 9 (B1)-(B3)
This will be described with reference to FIGS. 9 (C1) to 9 (C3) and FIGS. 10 (A), (B) and (C). In this embodiment, each part of the first to sixth lenses L1 to L6 is configured as shown in Table 5 below.

Further, the axial distances d2, d4, d9, d11 in the first lens L1 to the sixth lens L6 in which the respective parts are set as shown in Table 5
Is changed as shown in Table 6 below according to each magnification.

The zoom lens formed by the first to sixth lenses L1 to L6 and the like each having its components set as shown in Tables 5 and 6 has a lens configuration diagram at the time of enlargement (m = 2.0) shown in FIG. Figure (A)
FIG. 8 (B) shows a lens configuration at the time of equal magnification (m = 1.0), and FIG. 8 (C) shows a lens configuration at the time of reduction (m = 0.5).

Also in this embodiment, in the same manner as in each of the above-described embodiments, the conjugate length from the object plane to the image plane is kept constant irrespective of whether the magnification is the same or not, and the magnification is copied continuously. A mechanical zoom lens is obtained.

Also, in the third embodiment, the on-axis intervals d6 and d7 are fixed to 0.300, and the zoom movement is performed in the first and second embodiments in the same manner as the above-described second embodiment.
Second, by moving only the fifth and sixth lenses L1, L2, L5 and L6, the third and fourth lenses L3 and L4
Denotes a fixed lens group.

Further, spherical aberration diagrams corresponding to the lens configuration diagrams corresponding to enlargement, equal magnification, and reduction, respectively, shown in FIGS. 8 (A), (B), and (C) are shown in FIG. 9 (A1), (B1) and (C1), astigmatism aberration diagrams are shown in FIGS. 9 (A2), (B2) and (C2), and distortion aberration diagrams are shown in FIG. 9 ( Shown in A3), (B3) and (C3).

Similarly, coma aberrations are shown in FIGS. 10 (A), (B), and (C) in correspondence with enlargement, equal magnification, and reduction.

Next, FIGS. 11 (A), (B) and (C) showing FIGS. 11 (A), (B) and (C), and FIGS. 12 (A1) to 12 (A) showing the fourth embodiment of the present invention for each of the states at the time of enlargement, equal magnification and reduction. A3), Fig. 12 (B1)-(B3)
And FIG. 12 (C1) to (C3) and FIG. 13 (A),
This will be described with reference to (B) and (C). This example is
Each part of the first to sixth lenses L1 to L6 is configured as shown in Table 7 below.

Further, as shown in Table 7, the axial distances d2, d4, d6, d7, in the first lens L1 to the sixth lens L6 in which each part is set.
d9 and d11 are changed as shown in Table 8 below.

As shown in Tables 7 and 8, the zoom lens formed by the first to sixth lenses L1 to L6 and the like in which each part is set has a lens configuration diagram at the time of enlargement (m = 2.0). Figure (A)
FIG. 11 (B) shows a lens configuration diagram at the same magnification (m = 1.0), and FIG. 11 (C) shows a lens configuration diagram at the time of reduction (m = 0.5).

In this embodiment, similarly to the above-described embodiments,
Thus, a zoom lens for a variable magnification copying machine is provided in which the conjugate length from the object plane to the image plane is kept constant irrespective of the same magnification and at the time of zooming, and continuously zooms.

FIG. 11A, FIG. 11B, and FIG. 11C show spherical aberration diagrams corresponding to the lens configuration diagrams corresponding to enlargement, equal magnification, and reduction, respectively, in the same manner as described above. 12 (A1), (B1) and (C1), astigmatism is shown in FIGS. 12 (A2), (B2) and (C2), and distortion aberration diagrams are shown in FIG. 12 (A3). Shown in (B3) and (C3).

Similarly, for coma aberration, FIG.
(B) and (C).

Next, FIGS. 14 (A), (B) and (C) and FIGS. 15 (A1) to (A3) show the fifth embodiment of the present invention in each of the states at the time of enlargement, equal magnification and reduction. ) (B1)-(B3) and (C
This will be described with reference to 1) to (C3) and FIGS. 16 (A), (B) and (C). In this embodiment, the first to sixth lenses L1
To L6 are configured as shown in Table 9 below.

Further, the axial distances d2, d4, d9, d11 in the first lens L1 to the sixth lens L6 in which the respective parts are set as shown in Table 9
Is varied as shown in Table 10 below.

The zoom lens formed by the first to sixth lenses L1 to L6 and the like each having its components set as shown in Tables 9 and 10 has a lens configuration diagram when enlarged (m = 1.414). FIG. 14A shows a lens configuration at the same magnification (m = 1.0) in FIG. 14B, and FIG. 14C shows a lens configuration at the time of reduction (m = 0.707). Is shown.

In this embodiment, similarly to the above-described embodiments,
Thus, a zoom lens for a variable magnification copying machine is provided in which the conjugate length from the object plane to the image plane is kept constant irrespective of the same magnification and at the time of zooming, and continuously zooms.

Also, in the fifth embodiment, similarly to the above-described second and third embodiments, the third and fourth lenses L3 and L4 are fixed lens groups, and the first, second, fifth and sixth lenses L1, L2 , L5 and
L6 is for zoom movement.

Also, the aberration diagrams of spherical aberration corresponding to the lens configuration diagrams corresponding to enlargement, equal magnification, and reduction at the same time as shown in FIGS. 14 (A), (B) and (C) are shown in FIG. Fig. 15 (A1), (B1) and (C1) show astigmatism aberration diagrams in Fig. 15 (A2), (B2) and (C2),
Fig. 15 (A3), (B3) and (C)
See 3).

Similarly, for coma aberration, FIG.
These are shown in (B) and (C), respectively.

Next, FIGS. 17 (A), (B) and (C) and FIGS. 18 (A1) to 18 (A1) to 18 (A1) to (C) show the sixth embodiment of the present invention for each of the states of magnification, equal magnification and reduction. A3), (B1) to (B3) and (C1) to (C3) will be described with reference to FIGS. 19 (A), (B) and (C). In this embodiment, the first to sixth lenses
Each part of L1 to L6 is configured as shown in Table 11 below.

On-axis spacing d2, d4, d6, d7, d9, d11 in Table 11 above
Takes different values at the time of equal magnification and at the time of zooming. In other words, the second to fifth lenses L2 to L5 move as shown in Table 12.

As shown in Tables 11 and 12, a zoom lens formed by first to sixth lenses L1 to L6 and the like in which each part is set has a lens configuration at the time of enlargement (m = 2.0). Figure (A)
FIG. 17 (B) shows a lens configuration at the time of equal magnification (m = 1.0), and FIG. 17 (C) shows a lens configuration at the time of reduction (m = 0.5).

In this embodiment, similarly to the above-described embodiments,
Thus, a zoom lens for a variable magnification copying machine is provided in which the conjugate length from the object plane to the image plane is kept constant irrespective of the same magnification and at the time of zooming, and continuously zooms.

In the case of the sixth embodiment, the third lens L3 is fixed during zooming between the same magnification and reduction, while the fourth lens L4 is zoomed between the same magnification and magnification. It is considered immovable during times.

Here, focusing on changes in the axial distance d2 between the first lens L1 and the second lens L2 and the axial distance d11 between the fifth lens L5 and the sixth lens L6, the first embodiment will be described. Similarly, the movement amounts of the first lens L1 and the sixth lens L6 are
It can be seen that the image is moved by a symmetric value with respect to each of the enlargement and the reduction.

FIGS. 18 (A1), 18 (A1), and 18 (A1) show the aberration diagrams of the spherical aberration corresponding to the lens configuration diagrams at the time of magnification, at the same magnification, and at the time of reduction, respectively, shown in FIGS. ),
(B1) and (C1) show astigmatism aberration diagrams in FIGS. 18 (A2), (B2) and (C2), and distortion aberration diagrams in FIGS. 18 (A3) and (B3). And (C3).

Similarly, the coma aberration is also shown in FIG.
(B) and (C).

In the first to sixth embodiments described above, the above-mentioned condition, that is, the condition of 0.6 <| f1 / f0 | <0.7 and the condition of 0.35 <| f2 / f0 | <0.43 is, of course, satisfied. And
This value is shown in Table 13 below.

As is clear from Table 13 above, it can be seen that all the examples satisfy the above conditional expression.

As is clear from the aberration diagrams of the first to sixth embodiments, in each of the embodiments, the on-axis and off-axis balances are very good at each magnification, and the coma Looking at the aperture efficiency is almost 100%,
It can be seen that the flare component is very small and well corrected.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, despite having a six-group, six-element structure and a small number of lenses, at least the first lens and the sixth lens are asymmetrically moved, thereby increasing the magnification by 0.5 times. Various aberrations are satisfactorily corrected in a very wide range of magnifications from 1.times. To 2.0. Thus, a compact zoom lens for a variable magnification copier having very high contrast at any magnification can be provided.

Further, according to the present invention, since the magnification over a wide range can be obtained as described above while keeping the conjugate length from the object plane to the image plane constant, the folding mirror and the like are driven in conjunction with the zoom movement. A conventional mechanism is not required, and a variable magnification copying machine having a very simple configuration can be provided.

In addition, according to the present invention, the six groups and six lenses form a zoom lens using three pairs of the same lens.
A zoom lens for a variable-magnification copying machine which is advantageous in terms of manufacturing and schematic management, and which is inexpensive, can be provided.

[Brief description of the drawings]

FIGS. 1 to 4 (A) to 4 (C) are views for explaining the first embodiment of the present invention, and FIG.
FIG. 2 is a lens configuration diagram showing a basic configuration of a zoom lens for a variable magnification copier, FIG. 2A is a lens configuration diagram at the time of enlargement, and FIG. 2B is a lens configuration diagram at the same magnification. ,
FIG. 2 (C) is a lens configuration diagram at the time of reduction, and FIGS. 3 (A1), (A2) and (A3) are spherical aberrations at the time of enlargement.
FIG. 3B is an aberration diagram showing astigmatism and distortion, respectively.
1), (B2) and (B3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the same magnification, and FIGS. 3 (C1), (C2), and (C3) are diagrams at the time of reduction. Spherical aberration,
FIG. 4A is an aberration diagram showing astigmatism and distortion aberration, and FIG.
FIG. 4B is an aberration diagram showing coma aberration at the time of equal magnification, FIG. 4C is an aberration diagram showing coma aberration at the time of reduction,
FIGS. 5 (A) to 5 (C) to 7 (A) to 7 (C) are diagrams for explaining a second embodiment of the present invention.
5 (A) is a lens configuration at the time of enlargement, FIG. 5 (B) is a lens configuration at the same magnification, FIG. 5 (C) is a lens configuration at the time of reduction, and FIG. 6 (A1), (A2) and (A3) show the spherical aberration at the time of enlargement.
FIG. 6B is an aberration diagram showing astigmatism and distortion, respectively.
1), (B2), and (B3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the same magnification, and FIG.
1), (C2) and (C3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the time of reduction, and FIG. 7 (A)
FIG. 7B is an aberration diagram showing coma aberration at the time of enlargement, FIG. 7B is an aberration diagram showing coma aberration at the same magnification, and FIG.
FIG. 8C is an aberration diagram showing coma aberration at the time of reduction, and FIGS. 8A to 8C to 10A to 10C illustrate a third embodiment of the present invention. 8 (A) is a lens configuration diagram at the time of enlargement, FIG. 8 (B) is a lens configuration diagram at the same magnification, and FIG. 9 (A1), (A2), and (A3) show the spherical aberration at the time of enlargement.
9A and 9B show astigmatism and distortion, respectively.
1), (B2), and (B3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the same magnification, and FIG.
1), (C2), and (C3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the time of reduction, and FIG. 10 (A)
Is an aberration diagram showing coma at the time of enlargement, FIG. 10 (B) is an aberration diagram showing coma at the same magnification, and FIG.
FIG. 9C is an aberration diagram showing coma aberration at the time of reduction, and FIG.
FIGS. 11 (A) to 11 (C) to FIGS. 13 (A) to 13 (C) are views for explaining the fourth embodiment of the present invention, in which FIG. FIG. 11 (B) is a lens configuration diagram at the time of equal magnification, and FIG.
FIG. 11 (C) is a lens configuration diagram at the time of reduction, and FIGS. 12 (A1), (A2) and (A3) are spherical aberrations at the time of enlargement.
Aberration diagram showing astigmatism and distortion respectively, FIG. 12 (B
1), (B2) and (B3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the same magnification, and FIG. 12 (C)
1), (C2), and (C3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the time of reduction, and FIG. 13 (A)
Is an aberration diagram showing coma at the time of enlargement, FIG. 13 (B) is an aberration diagram showing coma at the same magnification, and FIG.
FIG. 9C is an aberration diagram showing coma aberration at the time of reduction, and FIG.
FIGS. 14 (A) to (C) to FIGS. 16 (A) to (C) are views for explaining the fifth embodiment of the present invention, in which FIG. FIG. 14 (B) is a lens configuration diagram at the same magnification, and FIG.
FIG. 14 (C) is a lens configuration diagram at the time of reduction, and FIGS. 15 (A1), (A2) and (A3) are spherical aberrations at the time of enlargement.
An aberration diagram showing astigmatism and distortion, respectively, and FIG. 15 (B
1), (B2), and (B3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the same magnification, and FIG.
1), (C2) and (C3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the time of reduction, and FIG. 16 (A)
Is an aberration diagram showing coma aberration at the time of enlargement, FIG. 16 (B) is an aberration diagram showing coma aberration at the same magnification, and FIG.
FIG. 9C is an aberration diagram showing coma aberration at the time of reduction, and FIG.
FIGS. 17 (A) to 17 (C) to FIGS. 19 (A) to 19 (C) are views for explaining the sixth embodiment of the present invention, in which FIG. FIG. 17 (B) is a lens configuration diagram at the time of magnification, and FIG.
FIG. 17 (C) is a lens configuration diagram at the time of reduction, and FIGS. 18 (A1), (A2) and (A3) are spherical aberrations at the time of enlargement.
Aberration diagram showing astigmatism and distortion respectively, FIG. 18 (B
1), (B2), and (B3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the same magnification, and FIG. 18 (C)
1), (C2), and (C3) are aberration diagrams respectively showing spherical aberration, astigmatism, and distortion at the time of reduction, and FIG. 19 (A)
Is an aberration diagram showing coma aberration at the time of enlargement, FIG. 19 (B) is an aberration diagram showing coma aberration at the same magnification, and FIG.
FIG. 9C is an aberration diagram showing coma aberration at the time of reduction. 1 to 13: surface, r1 to r13: radius of curvature, d1 to d12: axial distance, L1: first lens, L2 ... second lens, L3 ... third lens, L4 ... fourth Lens, L5: Fifth lens, L6: Sixth lens, N1 to N6: Refractive index of first to sixth lenses, v1 to v6: Abbe number of first to sixth lenses.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Ichinomiya 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-2-181714 (JP, A) JP-A Sho 63-180927 (JP, A)

Claims (1)

(57) [Claims] A first lens comprising a meniscus concave lens having a concave surface facing the object side in order from the object surface to the image surface;
A second lens composed of a convex lens, a third lens composed of a meniscus concave lens with a concave surface facing the object side, a diaphragm, a fourth lens composed of the same lens as the third lens and having a concave surface facing the image plane, The fifth lens which is the same lens as the second lens
What is claimed is: 1. A zoom lens for a variable magnification copying machine having a six-group, six-element configuration in which a lens and a sixth lens having the same lens as the first lens and having a concave surface facing the image plane are arranged. When forming an image on the image surface at a magnification of 2, the first to sixth lenses are arranged symmetrically with respect to the stop, and the focal length of the first lens is f1 and the focal length of the second lens is f2. When the combined focal length of the whole lens system at the same magnification is f0, 0.6 <| f1 / f0 | <0.7 and 0.35 <| f2 / f0 | <0.43 When an image is formed on an image plane, at least the first lens and the sixth lens among the first to sixth lenses and the diaphragm are asymmetrically moved, and the entire lens system is moved in the optical axis direction. No continuous zooming possible while keeping the conjugate length from the surface to the image plane constant regardless of whether the magnification is 1 or 2 The zoom lens for zooming copier, characterized in that.