JPS6239811A - Copying use variable power lens - Google Patents

Abstract

PURPOSE:To obtain the titled lens of a small size constituted of a small number of pieces, by making an optical system constituted of two lens groups having positive and negative focal distances in order from an object side, and making said optical system satisfy a prescribed condition. CONSTITUTION:Variable power is executed by varying an interval of the first lens group and the second lens group, also moving the whole, and keeping a distance between an object surface and an image formation surface constant. Also, the first lens group is constituted of three pieces of the first positive lens, the second negative lens and the third positive lens, and satisfies a condition of an inequality. In this regard, in the inequality, a focal distance in 1.00X of the whole lens system, and a focal distance of the first lens group are denoted as fM, and fI, respectively.

Description

[Detailed description of the invention] a. Technical field The present invention has a brightness comparable to that of FNOI and a viewing angle of 2.
This invention relates to a variable magnification (zoom) lens for copying with a constant distance between objects and which can cover up to approximately ω=40°.

b. Prior Art and its Problems In recent years, as copying machines have been increasingly required to be smaller and lower in cost, lenses for copying machines have also been desired to be smaller and lower in cost. We also offer copy machines that can be enlarged and reduced.
There is also a growing need for variable magnification (zoom) lenses for reducing images. Conventionally, as a variable magnification lens for copying, for example, JP-A-57-68810, JP-A-60-5731
No. 1 is known, but the former consists of 8 lenses and the latter consists of 7 lenses, which were not sufficient in terms of miniaturization and cost reduction.

Furthermore, with the aim of miniaturization, Japanese Patent Application No. 123991/1987 was proposed by the same applicant, which consists of six sheets and has achieved miniaturization and cost reduction. However, in this example, the amount of change in lens spacing during zooming is still large, and it cannot be said that sufficient miniaturization has been achieved, and there is still room for improvement.

C1 Purpose The present invention has been made to solve the above-mentioned problems, and is a further improvement of the above-mentioned Japanese Patent Application No. 123991/1985, and achieves a large magnification ratio and good performance while satisfying both of the requirements of small size and low cost. The object of the present invention is to provide a variable magnification lens for copying.

d0 Configuration of the Invention In order to achieve the above-mentioned object, the variable magnification lens for copying of the present invention is composed of, in order from the object side, a lens group having a positive focal length and a lens group 2 having a negative focal length. is,
In a variable magnification lens for copying that changes the distance between the first lens group and the second lens group and moves the entire lens group to maintain a constant distance between the object plane and the image forming plane, the first lens group The group consists of a positive first lens, a negative second lens and a positive third lens.
It is composed of three lenses and is characterized by satisfying the following condition (1).

(1) 0.35< f r / f M <0.85
Further, the variable magnification lens for copying having the above configuration is further characterized in that it is configured to satisfy the following conditions (2) to (5).

(2) 0.2<-f I-2/fM<0.4 (f
1.2 <0) (3) 0.7<f x +l/f
1.3 <2.0(4) 0.35< P Summer
<1.3(5)! v s 1 <0.04 However, furthermore, in the variable magnification lens for copying configured as described above, the No. 1 lens group is composed of two lenses, a positive lens and a negative lens,
Alternatively, it is characterized by being composed of one negative lens, and the Ⅰth lens group is under the following conditions (6) and (7).
).

(6) 0.6<-f rr / f M<3.3
(f n <O) (7) -0,06<V n < 0 However.

In addition, the present invention provides a variable magnification lens for 22-sheet copying,
It is characterized by a structure in which the object plane and the imaging plane are interchanged.

Note that the symbols in each of the above conditions are determined as follows.

fM: Focal length fI of the entire lens system at + and OO×:
Focal length of the first lens group f■: Focal length of the ■th lens group fTri: Focal length of the i-th lens of the ■th lens group nI+
i: refractive index νIri of the j-th lens in the first lens group; Atsube number fII++ of the i-th lens in the lens group; focal length ν of the i-th lens in the ■-th lens group; Effect of Lens Abbe Number 01 Each of the above conditions will be explained below according to the configuration.

The most distinctive feature of the present invention is that the main components of this type of variable magnification lens for copying are at least 4.
The first lens group, which used to be composed of 6 to 6 lenses, can now be made up of 3 lenses in 3 groups, which is the minimum necessary. For this purpose, the ratio of the focal length of the first lens group to the focal length of the entire system is an important structural requirement. Condition (1) determines this. If the upper limit is exceeded, the power of the first lens group decreases, which is advantageous in terms of aberration correction, but the power of the The amount of interval change increases,
It becomes difficult to downsize. On the other hand, when the lower limit is exceeded and the power of the first lens group increases, the weight of aberration correction of the first lens group increases compared to the aberration correction of the entire system, resulting in large aberration fluctuations during zooming, and manufacturing errors. The sensitivity of each lens element to this becomes excessive, making it difficult to maintain good performance.

Furthermore, by adding conditions (2) to (5), the positive t-th lens group can appropriately distribute the lens power within the 1121st lens group and achieve flatness of the image plane, which is important as a copying lens. This is effective for good correction of various aberrations including dichromatic aberration.

Condition (2) relates to the power of the negative second lens in the 1121st group. In this condition (2), when the upper limit is exceeded, the negative power of the second lens becomes smaller, and along with this, the positive power of the first lens becomes smaller. The power of both the third lenses is small, and the correction of spherical aberration and coma aberration becomes 4i advantageous, but it becomes difficult to correct chromatic aberration.

On the other hand, if the upper limit is exceeded, the power of each lens in the first lens group becomes excessive, causing extremely large coma aberration, and reducing the MTI at low frequencies, which is important for copying lenses. will decrease.

Condition (3) means that the large positive power in the 1121st group is
This is a condition for obtaining good aberration correction by distributing it to the first lens and the third lens. In this condition (3), if the limit is exceeded, the positive power of the first lens becomes too small, and it is difficult to sufficiently correct the spherical aberration and astigmatism occurring on both surfaces of the second lens. If the lower limit is exceeded, the positive power of the first lunion becomes excessive, the asymmetry of the first lens system increases, distortion aberration increases, and spherical aberration occurs noticeably on the first surface of the first lunion, resulting in a good image. I can't get the aberration.

Condition (4) is a condition for Petzval sum correction in the Luns group. The first lens group is the main lens group for aberration correction, and Petzval sum correction is an important requirement in order to obtain uniform and good performance over a wide angle of view like a copying lens. If the upper limit of condition (4) is exceeded, the Petzval sum becomes excessive and it is difficult to obtain a flat image plane. In addition, if the lower limit is exceeded, the positive first . The third lens requires an expensive high-refractive, low-dispersion glass material, which goes against the goal of lowering the price.Furthermore, since the power of each lens increases, the sensitivity to manufacturing errors becomes excessive, resulting in a decrease in quality during manufacturing. A problem arises.

Condition (5) is a condition for correcting chromatic aberration in the first lens group. In a zoom lens such as the present invention, it is necessary that chromatic aberration be corrected to some extent in each group in order to guarantee performance during zooming.

In particular, since the r-th lens group is the main lens group for correcting aberrations, condition (5) is important. This condition (5)
If the value exceeds , the chromatic aberration generated in the first lens group becomes excessive, and even if it is corrected to some extent in the first lens group, the chromatic aberration will fluctuate during zooming, making it difficult to obtain good performance over a wide zooming range. It is difficult.

Next, the 1121st group will be explained.

The main function of the 1121st lens group is to correct changes in the object-to-image distance when changing magnification, and to keep the object-to-image distance constant even when changing magnification. This is to obtain aberrations in which the aberrations slightly remaining in the 1121st group are finally well corrected. Therefore, the 1121st lens group has a smaller negative power than the first lens group, and can also have a smaller number of lenses.

In the present invention, the 1121st group is achieved by having two positive and negative lenses or one negative lens.

The conditions regarding the 1121st group will be explained below.

Condition (6) relates to the power of the entire lens group (2). The negative power of the 1121st group is related to the positive power of the lens group and the distance from the 1121st group, in order to maintain good aberrations over a wide zooming range and to obtain a compact lens. is important. In this condition (6), the power of the 1121st group decreases beyond the eye, and aberration fluctuations during zooming are suppressed to a small level, but changes in lens group spacing during zooming become large, resulting in miniaturization. becomes difficult. On the other hand, if the lower limit is exceeded, the change in lens group spacing during zooming will be small and the lens will become compact, but variations in various aberrations including spherical aberration and dichromatic aberration will increase during zooming, making it difficult to obtain a wide zooming range. becomes difficult.

Moreover, condition (7) is a chromatic aberration correction condition for the 1121st group. Since the 1121st lens group is a negative lens group as a whole, the value of condition 1 (7) usually has a negative value.
If the lower limit is exceeded, the amount of chromatic aberration correction in the 1121st group becomes excessive, and even if chromatic aberration is corrected at a specific magnification, the chromatic aberration will fluctuate during zooming. In addition, in this condition (7),
When the 1121st group has a single-element structure, it can be considered that fUz2'', so it can be expressed as follows.

By satisfying the constituent requirements of the 1121st lens group as described above, as shown in the examples, good aberrations can be obtained regardless of whether the 1st lens group is arranged as positive, negative, or negative or positive. When placing emphasis on the symmetry of the lens system, it is better to place a negative lens as the first lens from the object side of the 1121st lens group after the lens group, and a positive lens as the second lens to reduce aberrations. This is advantageous in terms of correction.

Also, by configuring the 1121st group with a single negative lens, a wide range of magnification is possible while maintaining practically sufficient aberrations, as shown in the embodiments. However, it is natural that variations in longitudinal chromatic aberration and lateral chromatic aberration depending on the magnification are slightly larger than when the 1121st group is composed of two positive and negative lenses.

The present invention has the above-mentioned configuration, and achieves the objective of small size and
Although it is possible to obtain a variable magnification lens for copying that is inexpensive, has a wide variable magnification range, and has good performance, even better performance can be obtained by adding the following conditions to the configuration of the lens group. It will be done.

(8) 0.7<r r/r 4<1.4('
9) 0.7< d a / d 2 < 10 (1
0) 0.4< l r5/ r6 1 <2
(re <O) Condition (8) is a condition for satisfactorily correcting spherical aberration. The first surface (rl) of the first lens and the second surface (r4) of the second lens tend to have large spherical aberration coefficients,
By maintaining these relationships as in condition (8), spherical aberration can be kept small.

When the upper limit or lower limit of condition (8) is exceeded, spherical aberration becomes significantly over-corrected or under-corrected, respectively.

Condition (9) is a condition regarding the positional relationship in the optical axis direction of the lenses of the (1)th lens group triplet. When the upper limit of condition (9) is exceeded, the meridional image plane at one peripheral angle of view becomes significantly undersized, and when the lower limit is exceeded, the meridional image surface becomes oversized and spherical aberration occurs.

Comatic aberration deteriorates significantly.

Condition (10) defines the shape of the third lens. Both surfaces (rs, re) of the third lens also have strong positive power, and the radius of curvature of the first lens is balanced. Aberrations generated by the second lens are corrected. If the upper or lower limit of condition (10) is exceeded, it becomes difficult to balance the correction of spherical aberration and coma aberration.

Also, when the negative lens group #1 is composed of one lens,
If the following conditions are further added, good aberration correction can be obtained.

(II) 0.3 < f M / r 7 < 2 If the upper limit or lower limit is exceeded in condition (11), coma aberration,
Astigmatism deteriorates, and the aberration changes significantly during zooming.

As described above, in the present invention, the first lens group has positive power and the second lens group has small negative power, but this is because the lens system is installed in a space such as a copying machine. In this case, the distance from the object surface (original surface) to the lens can be longer than the distance from the lens to the imaging surface (photoreceptor surface). This is advantageous when a space for a scanning mirror is required, or when a similar effect is desired in terms of the configuration of a copying machine.

In addition, since the object plane and the imaging plane are conjugate planes, it is naturally possible to replace the object plane and the imaging plane in the present invention.

In this case, the distance from the image forming surface to the lens surface can be made larger than the distance from the lens surface to the object surface, and the degree of freedom in the configuration of the copying machine can be increased.

f. Examples Below, numerical values of examples of the present invention will be described. Here, FN
O is the F number + fM is the focal length of the entire lens system at 1.00x, 2ω is the viewing angle of 1 m is the variable magnification range, r is the radius of curvature of each lens surface, d is the lens thickness or distance between lenses, and n is the distance between each lens. The refractive index, ν, is the Abbe number of each lens. still,
Each value of the conditional expression is calculated using the e-line as a reference wavelength.

[Example 1] FNol: 6.7 f M=188.059 2
ω=42°~36°m=-1,42X~-0,64X Plane Na r d 1 37.88] 7.48 1. ．． 65844
50.92 1.2B, 810 4.13 3 -206.660 2.01 1. , 6200
4 36.34 37.833 14.70 5 108.4+4 5.15 1.65160 5
8.56 -88.437 3.00~12.347
232.395 5.116 1.64769 3
3.88-133.867 1.90 9-111.991 2.20 1.59551 3
9.210 94.121 (conditional expression) % expression% (conditional expression) (1) f I /fM=0.669 (2) f
x, 2/fM=0.264(3)fx,t/fI
, 3=0.954 (4) P engineering=0.655 (5) V
I=0.012 (6) fn/fM=1.5
03(7)Vn=-0,018(8)r1/r4=
0.969(9)da/d2=3.950 (1,
0)rs/r6=1-. 522 [Example 3] F uo 1 : 6.7 f M =187.76
7 2 (J = 42°~36″m==-1.42X~
-〇, 64X plane Nn d nl 40.
371 9.06 1.70000 47.32 1
22.344 3.87 3-166.426 2゜00 1.64769 3
3.84 42.272 13.17 5 136.773 5.25 1.65844 5
0.96 -80.755 3.00~16.657
36B, 379 5.64 1.64769 33
．． 88-103.379 2.66 9 -89.348 i, 50 1.62004
36.310 140.566 (conditional expression) % expression% (conditional expression) (1) fr/fM=0.560 (2) - f□, 2
/fM=0.275(3)fr,! /fx, 3=1.
099 (4) P1=0.585 (5) Vt= 0
．． 007 (6) fn/fH=1.097(7)
Vn” 0.013 (8)rs/ra=1
．． 065(9)da/d2=1.929(10)t
5/rIl, = -0,712 [Example 5] FNOI: 6.7 fM = 188.800 2ω =
42″~36″m=-1, 42X~-〇, 64X Surface Nα r d n ν1 3
7.375 7.00 1.71700 47.92
145.132 3.97 3 -454.520 2.00 1.64769
33.84 33.653 10.64 5 65.725 5.00 1.67'? '30
53.36-118.041 3.00-6.79
7 -332.384 2.00 1.51633
64.18 60.969 13.00 9 204.01? 4.00 1.50657
62.010-84B, 356 (conditional expression) % expression% (conditional expression) (1) f r /fM=0.673 (2) -f
I,2/fM=0.265(3)fx,t/
f r ,3 =0.971 (4) P r =0.
651(5)V ■=-0,012(6) f n
/fM=1.525(7)Vn=-0,017(
8) rt/r4=Q. 969(9)da/d2
=3.865 (10)r5/rs =-1,49
8 [Example 7] t' lro ]: 6.7 f
M = 188.512 2 ω =
42″ ~ 36゜m=-1.]42X--0.64 XNo d n ν1
41.365 6.68 1.71300 53.8
2 +11.023 4.43 3 -1!16.886 3.00 1.60342
38.04 42.064 12.29 5 126.055 4.28 1.71300 5
3.86 -99.630 3.00~15.1.9
7 211.976 2.00 1.51n72 4
1.28 59.691 1.85 9 62.044 5.07 1.6584450
．． 910 90.522 (conditional expression) % expression% (conditional expression) (1) f r /fM=O', 617 (2) f
x, 2/fM=f1.289 (3) fr, t/
fx, 3=1.080 (4) P□=0.672(5
)VI=-0,003(6)-fn/fM=
1.324(7)Vn =-0,016(8)r+l
ro=1.052(9)da/d2=3.436
(10)rs/r6 =-1,0011(11)f
M/r7=0.934 [Example 9] FNOI: 6.7 f M ”189.039
2 c, + = 42° ~ 366m = -1,42X ~ -t
'1.64X plane Nn r d n ν1
:'17.423 6.38 1.6Q61'
10 55.52 ]+9. l+45/1.
073 -322.14rl 1.80 1.60
342 38.04 35.362 14.52 5 94.811. 4.46 1.72 (HIO
50,36-116,84+ 3. nO~9.52
7 181'1.166 2.11 1.58+4
4 50.88 7C9! '11 (conditional expression) % expression% (conditional expression) (1) f r /fM=0.740 (2) f
+,2/fM=0.211(3)f! , 1/fx,
3=1.581 (4)PH=0.495(5)V■
= −0,016(6) fm/fr−x=2.45
6 (7) V n =0.006 (8) r I lr
o ~11. Q14(9)da/d2=1.291
(10)rs/r6=-1.483(11)fM/
r7=0.856 [Example 11] FHo 1 : 6.7 f M =]8n, 410
2 ω=42°~36°m=-1,42X −-0,
64X plane Nn r d nl 43.
245 5.73 1.72916 54.7213
0゜460 7.58 3 -216.643 1.80 1.61293
37.04 41.000 13.82 5 105.520' 4.31 1.71300
53.86-109.228 3.00-12.22
7 219.229 2.11 1.50137 5
6.48 84.243 (conditional expression) % expression% (conditional expression) ' (1) ft/f)4=0.515 (2) fx,
2/fM=0.274(3)fx,t/ft,+=0.
969 (4)P1=0.845(5)'V,=0
．． 009 (6) f n /fM=0.900(
7) Vn=-0,027(8)rt/r4=1.11
5(9)d4/d2 =6.370 (to)rs
/rB = 0.662(11)f)4/r7 =
1.076 = 27- [Example 13] F, ol: 6.7 f M = 188.940 2
ω;42a~366m=-1,42X --0,64X surface &d n 1 36.092 6.44 1.72916 5
4.72 120.718 2.48 3 -738.498 1.80 1.5814/1
40.74 31.8nO17,79 5' 81.786 4.6+ 1.69351
1 53.26-117.211 3.0n~8.0
67 197.585 2.11 1.53172
48.98 64.447 (conditional expression) % expression% (conditional expression) (1) f K/fM=0.527 (2) f I
,2/fM=0.260(3)f 1.1/f 1
．． 3 = 1.100 (4) P s = 0.798 (
5) V X=0.008 (6)-f I[/fH=
0.954(7)Vn” 0.032(8)r
t/r4=1.039(9)da/d2"5.
46 (10)rs/r6 = 0.801(1
1) fM/r? = 1.175 g, more than effective d (As mentioned above, according to the present invention, conventionally 6 groups and 8
The variable magnification 1/lens for copying, which used to be composed of 6 lenses in 6 groups, can be achieved with an extremely small structure of 5 lenses in 5 groups or 4 lenses in 4 groups. Reducing the number of components has a great effect on miniaturization and lower cost, and the object of the present invention can be fully achieved. Furthermore, as in the example, the brightness is in the diameter ratio FI: 6.7 class, and the magnification range is -1.42x to -0.6/IX.
It is now possible to obtain good performance while satisfying the same specifications as the 8-element or 7-element lens system exemplified as the prior art.

[Brief explanation of drawings]

1st, 5th", 9, 13. +7.21., 25.
29.33.37°/II, 45.49.53 figure is
Examples 1, 2, 3 of the present invention 4, 5. 6. 7.
8. 9.10. II, +2.13.1.4 lens sectional view. No. 21g, 1.0', 14.18.22.26.
30.34.3B. 42, 46, 50, 54 are examples 1, 2, and 4 of the present invention.
3゜4, 5. 6. 7. 8. 9.10. II
, 12.13.14 aberration diagram at a magnification of 1.00×. 3', 7, 11. , 15.1! '1.23.27
．． 31.35.39゜43, 47.51.55 Figures show examples 1, 2, 3゜4, 5. 6.7.8. 9
．． 10.11.12.13.14 aberration diagram at a magnification of 1.42×. 4th, 8', 12.16.20.24.28.32
．． 36. 40° 44, 4g, 52. 56 Figures show embodiments of the present invention t, 2, 3° 4, 5. 6. 7. 8. 9
．． 10. II, 12.13.1.4 magnification 0.64
Aberration diagram at ×. Patent Applicant: Asahi Kogaku Kogyo Co., Ltd. ■ Letter of Amendment to Proceedings November 7, 1985, Japanese Patent Application No. 179595-16 Name of Invention Variable Magnification Lens for Copying 3, Relationship with the Person Making Correction Case Patent Applicant Address 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Name (0
52) 'M Kogaku Kogyo Co., Ltd. Representative Matsumoto Withdrawal 0 Agent Residence 2-36-9-6 Maeno-cho, Itabashi-ku, Tokyo Subject of amendment (1) "Detailed description of the invention" column of the specification, , 5th generation
(,,i,;,y,2RaC)Contents of the amendment (1) In the "Detailed Description of the Invention" section of the specification, in the 6th line of page 11, "Favorably amended... . . ." is corrected as "It corrects aberrations well.j.

Claims (1)

[Claims] 1. Consisting of, in order from the object side, a lens group I having a positive focal length and a lens group II having a negative focal length; In a variable magnification lens for copying, which changes the distance and moves the entire lens to maintain a constant distance between the object plane and the imaging plane,
The I-th lens group is composed of three lenses: a positive first lens, a negative second lens, and a positive third lens, and the focal length of the entire lens system at 1.00x is f_M, and the focal length of the I-th lens group is A variable magnification lens for copying, characterized in that it satisfies the following condition (1), where the distance is f_I. (1) 0.35<f_I/f_M<0.852, in the variable magnification lens for copying according to claim 1,
I The focal length of the i-th lens in the lens group is f_ I _, _i
, the refractive index of the i-th lens in the I-th lens group is n_ I _, _
i, the Abbe number of the i-th lens in the I-th lens group is ν_ I ＿
, _i, the variable magnification lens for copying is further configured to satisfy the following conditions (2) to (5). (2) 0.2<-f_ I _, _2/f_M<0.4(
f_ I _, _2 < 0) (3) 0.7 < f_I_, _1
/f_ I _,_3<2.0(4)0.35<P_ I<
1.3 (5) |V_ I |<0.04 However, P_ I =Σ＾3_i_=_1[f_M/(n_ I _,
＿i・f＿ I ＿、＿i)】V＿ I =Σ＾3＿i＿=＿
1 [f_M/(ν_ I _, _i・f_ I _, _i)]
3. The variable magnification lens for copying as set forth in claim 1 or 2, wherein the II lens group is composed of two lenses, a positive lens and a negative lens. . 4. A variable magnification lens for copying as set forth in claim 1 or 2, wherein the II lens group is constituted by one negative lens. 5. In the variable magnification lens for copying according to claim 3 or 4, the focal length of the II lens group is f_II,
When the focal length of the i-th lens from the object side of the II lens group is f_II_, _i, and the Abbe number of the i-th lens from the object side of the II lens group is ν_II_, _i, the I-th
The I lens group is a variable magnification lens for copying that satisfies the following conditions (6) and (7). (6) 0.6<-f_II/f_M<3.3(f_II<0
) (7) −0.06<V_II<0 However, V_II=[(1/ν_II_,_1・f_II_,_i)+
(1/ν_II_,_2・f_II_,_2)]×f_M6
A variable magnification lens for copying according to any one of claims 1 to 5, characterized in that the object plane and the imaging plane are interchanged.