JPH0640168B2 - Variable magnification lens for copying - Google Patents

Description

Detailed Description of the Invention

a. TECHNICAL FIELD The present invention has a brightness of about F _NO 1: 8 and a viewing angle of 2
The present invention relates to a variable magnification (zoom) lens for copying with a constant object-image distance, which can be embraced up to around ω = 40 °. b. 2. Description of the Related Art In recent years, there has been an increasing demand for downsizing and cost reduction of copying machines. Therefore, lenses for copying machines are also required to be small and low cost. In addition, enlargement / reduction copier and enlargement /
Similar needs are increasing for variable power (zoom) lenses for reduction. As the variable magnification lens for copying, conventionally, for example, JP-A-57-68810 and JP-A-60-57311 are known, but the former is composed of eight lenses and the latter is composed of seven lenses. It was not sufficient in terms of downsizing and cost reduction. Furthermore, for the purpose of downsizing, the same applicant proposed Japanese Patent Application No. 59-123991, which consists of 6 sheets,
It has achieved miniaturization and cost reduction. However, in this example, the amount of change in the lens spacing during zooming is still large, and it is difficult to say that sufficient miniaturization has been achieved, and there is room for improvement. c. The present invention has been made to solve the above problems,
It is an object of the present invention to further improve the above-mentioned Japanese Patent Application No. 59-123991 to provide a variable magnification lens for copying which has a large variable power and good performance while satisfying both of small size and low cost. d. Structure of the Invention In order to achieve the above-mentioned object, the variable magnification lens for copying of the present invention comprises, in order from the object side, an I lens group having a positive focal length and a II lens group having a negative focal length. In the variable magnification lens for copying, in which the distance between the I-th lens group and the II-th lens group is changed and the whole lens is moved to keep the distance between the object plane and the image formation surface constant, The fifth lens group is composed of a positive first lens element, a negative second lens element, a negative third lens element, and a positive fourth lens element, and the second lens element group II is a positive lens element with a large curvature surface facing the image side. And the sixth lens, which is a negative lens with the surface having a large curvature facing the object side, and further satisfies the following conditions. (1) 0.5 <f _I /fmax<0.7 (2) -0.7 <fmax / f1,2 <-0.1 (3) 0.3 <r ₇ /fmax<0.6 Further, the present invention is configured to satisfy each of the above conditions. The variable magnification lens for copying described above is characterized in that it further satisfies the following conditions. (4) 0.22> (n ₁ + n ₄ ) − (n ₂ + n ₃ )> 0.04 (5) 35> (ν ₁ + ν ₄ ) − (ν ₂ + ν ₃ )> 15 (6) 2.0 <−r ₃ / r ₄ <7.0 (7) 0.25 <f _{5 /} fmax <0.5 Further, the present invention provides a variable magnification for copying which is configured to satisfy the above conditions (1) to (3) or (1) to (7). The lens is characterized in that the image plane and the object plane are replaced with each other. However, in each of the above conditions, the code is determined as follows. fmax: focal length when the magnification of the entire system is equal magnification f _I : focal length of the I-th lens group f1, 2: sequentially from the object side, combined focal length of the first and second lenses r _i : sequentially from the object side, the curvature of the i-th surface radius n _i: refractive index of d line of the i-th lens [nu _i: Abbe number of the i-th lens f _5: focal length e of the fifth lens. Action Next, each of the above conditions will be described. The condition (1) defines the power of the positive I-th lens unit and is a condition for downsizing. In this condition (1), if the upper limit is exceeded, the power of each of the I and II lens groups will be small, the amount of change in the interval during zooming will increase, and miniaturization will be difficult. On the other hand, when the value goes below the lower limit, the amount of change in the distance becomes small, but the power of each lens group becomes excessive, and good aberration cannot be obtained. The condition (2) is a condition relating to power distribution in the I-th lens unit, and by setting the combined focal length of the first and second lenses in the I-th lens unit as the condition (2), negative as a whole,
It takes positive and negative power configurations and performs good aberration correction while maintaining strong power. In this condition (2), when the upper limit is exceeded, the negative power of the first and second lenses becomes small, and conversely, when the lower limit is exceeded, the negative power of the first and second lenses becomes excessive, and both the first power , The negative of the 2nd lens, the positive of the 3rd and 4th lens, and the negative of the 5th and 6th lens are broken, and it becomes difficult to satisfactorily correct aberrations. The condition (3) determines the shape of the fourth lens having a large positive power, keeps the various aberrations occurring in the first and second lenses small as the I-th lens group, and changes aberrations during zooming. Is a condition to keep the value small. In this condition (3),
When the upper limit is exceeded, it becomes difficult to correct the coma aberration generated on the second surface (r ₆ ) of the third lens, and when the lower limit is exceeded, it becomes difficult to correct spherical aberration, astigmatism, and distortion. By satisfying the above conditions (1) to (3), the main constitution of the present invention can be obtained, but by further adding the conditions (4) to (7), the object of the present invention can be achieved more effectively. can do. The condition (4) is a condition for keeping the Petzval sum small and making the configuration inexpensive. In this condition (4),
If the upper limit is exceeded, the Petzval sum will be overcorrected,
Further, since expensive high refractive index glass materials are used for the positive first and fourth lenses, it is not preferable. On the other hand, when the value goes below the lower limit, it becomes difficult to keep the Petzval sum small, and it becomes impossible to obtain a flat image surface. The condition (5) is a condition for correcting chromatic aberration. In this condition (5), if the upper limit is exceeded, the chromatic aberration is undercorrected, and if the lower limit is exceeded, the chromatic aberration is overcorrected, and good aberrations cannot be obtained. The condition (6) defines the shape of the second lens having a strong negative power. In this condition (6), if the upper limit is exceeded, the curvature of the second surface (r ₄ ) of the second lens becomes too small, spherical aberration remarkably increases, and higher-order coma aberration occurs and manufacturing errors occur. High sensitivity, which is a disadvantage. Even if the lower limit is exceeded, a good balance of coma and astigmatism cannot be obtained. The condition (7) is a condition of power in the second lens group II. In the present invention, the amount of change in the interval at the time of zooming is set to
This is achieved by increasing the power of the lens group.
Therefore, the second lens group II also has a strong negative power,
It is necessary for the entire II lens group to be corrected for aberrations satisfactorily, and by providing the positive fifth lens with power as in condition (7), good aberration correction is provided for the II lens group. In this condition (7), the upper limit is exceeded and the fifth
When the power of the lens becomes small, the high-order aberration correction effect by the second surface (r ₁₀ ) of the fifth lens and the first surface (r ₁₁ ) of the sixth lens decreases, and conversely, the lower limit is exceeded and the fifth lens is exceeded. If the power is increased, the change in aberration due to a manufacturing error increases, which is not preferable. f. Examples The numerical values of Examples 1 to 4 of the present invention will be described below. Where F _NO is the F number, 2ω is the viewing angle, r is the radius of curvature of each lens surface, d is the lens thickness or lens spacing, N is the d-line refractive index of each lens, and ν is the Abbe number of each lens. is there.

Example 1 F _NO 1: 8 2ω = 40 ° to 34 ° fmax = 206.98 Magnification ratio -1.42 × to -0.64 × Interval change amount during magnification change = 0.049 fmax Value of conditional expression (1) fI / fmax = 0.636 (2) fmax / f1,2 = -0.366 (3) r _{7 /fmax=0.470 (4) (n 1 +} n 4) - (n 2 + n 3) = 0.088 (5) (ν 1 + ν 4) - (ν 2 + ν 3) = 28.1 (6) -r 3 / r 4 = 4.648 (7) f ₅ /fmax=0.307

Example 2 F _NO 1: 8 2ω = 40 ° to 34 ° fmax = 207.06 Magnification ratio -1.42 × to -0.64 × Interval change amount during magnification change = 0.037 fmax Conditional expression value (1) fI / fmax = 0.596 (2) fmax / f1,2 = -0.458 (3) r _{7 /fmax=0.419 (4) (n 1 +} n 4) - (n 2 + n 3) = 0.167 (5) (ν 1 + ν 4) - (ν 2 + ν 3) = 21.1 (6) -r 3 / r 4 = 3.176 (7) f ₅ /fmax=0.394

Example 3 F _NO 1: 8 2ω = 40 ° to 34 ° fmax = 207.04 Magnification ratio -1.42x to -0.64x Interval change amount during magnification change = 0.041 fmax Conditional expression value (1) fI / fmax = 0.612 (2) fmax / f1,2 = -0.503 (3) r _{7 /fmax=0.449 (4) (n 1 +} n 4) - (n 2 + n 3) = 0.125 (5) (ν 1 + ν 4) - (ν 2 + ν 3) = 23.9 (6) -r 3 / r 4 = 4.114 (7) f ₅ /fmax=0.446

Example 4 F _NO 1: 8 2ω = 40 ° to 34 ° fmax = 207.09 Magnification ratio -1.42 × to -0.64 × Interval change amount during magnification change = 0.040 fmax Conditional expression value (1) fI / fmax = 0.613 (2) fmax / f1,2 = -0.313 (3) r _{7 /fmax=0.448 (4) (n 1 +} n 4) - (n 2 + n 3) = 0.125 (5) (ν 1 + ν 4) - (ν 2 + ν 3) = 23.9 (6) -r 3 / r 4 = 3.10 (7) f ₅ /fmax=0.441 g. Effect As described above, according to the present invention, the scaling factor −1.42 × to −0.64 ×
The amount of change in the interval at magnifications from 0.037fmax to 0.049
It is possible to obtain a variable magnification lens for copying which has a small fmax, is small and has a small number of constituent elements, and is inexpensive and has good performance.

[Brief description of drawings]

1, FIG. 5, FIG. 9, and FIG. 13 are lens configuration diagrams of Embodiments 1, 2, 3, and 4 of the present invention, FIG. 2, FIG. 6, and FIG.
10 and 14 show Embodiments 1, 2, 3, and 3 of the present invention, respectively.
4 is an aberration diagram at a magnification of -1 ×, FIG. 3, FIG. 7, and FIG.
FIG. 15 and FIG. 15 are aberration diagrams of Examples 1, 2, 3, and 4 of the present invention at a magnification of −1.42 ×, FIG. 4, FIG. 8, and FIG. 12, respectively.
FIG. 16 and FIG. 16 are aberration diagrams of Examples 1, 2, 3, and 4 of the present invention at a magnification of −0.64 ×, respectively.

Claims (3)

[Claims] 1. A first lens group having a positive focal length and a second lens group having a negative focal length are arranged in this order from the object side, and a distance between the I lens group and the second lens group is changed. In the variable magnification lens for copying, in which the entire distance is moved and the distance between the object plane and the image forming surface is kept constant to perform variable magnification,
The I-th lens group includes a positive meniscus first lens, a negative second lens, a negative third lens, and a positive fourth lens,
The II lens group is composed of a fifth lens, which is a positive lens with a surface having a large curvature facing the image side, and a sixth lens, which is a negative lens with a surface having a large curvature facing the object side, and further satisfies the following conditions. A variable magnification lens for copying, which is characterized by being configured as follows. (1) 0.5 <f _I /fmax<0.7 (2) -0.7 <fmax / f1,2 <-0.1 (3) 0.3 <r ₇ /fmax<0.6 where fmax: focus when the magnification of the entire system is equal Distance f _I : focal length of the I-th lens group f1,2: composite focal length of the first and second lenses in order from the object side r _i : radius of curvature of the i-th surface in order from the object side 2. A variable magnification lens for copying, characterized in that, in claim 1, it is constructed so as to further satisfy the following conditions. (4) 0.22> (n ₁ + n ₄ ) − (n ₂ + n ₃ )> 0.04 (5) 35> (ν ₁ + ν ₄ ) − (ν ₂ + ν ₃ )> 15 (6) 2.0 <−r ₃ / r ₄ <7.0 (7) 0.25 <f ₅ /fmax<0.5 where n _i : d-line refractive index of the i-th lens ν _i : Abbe number of the i-th lens f ₅ : focal length of the fifth lens 3. A variable magnification lens for copying according to claim 1 or 2, wherein the image forming surface and the object surface are replaced with each other.