JP2875964B2 - Zoom lens for copying - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens for copying which has a good aberration with a small number of lenses and has a constant object-image distance.

[0002]

2. Description of the Related Art A copying machine having a variable power function uses a single focus lens, and changes the distance between object images by moving a mirror.
The mainstream is to move and change the magnification of the entire lens system,
The disadvantage is that the mechanism is complicated and the device becomes large. On the other hand, if a zooming method in which the distance between the object and the image is fixed by the zoom lens is adopted, continuous zooming can be performed only by moving the zoom lens, and the entire apparatus can be reduced in size. Moreover, it was very difficult to obtain a zoom lens having good aberration. As a known example having a small number of components, there is a zoom lens described in Japanese Patent Publication No. 6-46261 having four components.
Since the negative lens is added to the rear of the triplet system and the distance between the triplet and the negative lens is changed at the time of zooming, the bias of the power arrangement increases, and distortion, asymmetric coma, Chromatic aberration of magnification is seen. On the other hand, a negative lens is added before and after the triplet, and these two negative lenses are moved at the time of zooming as Japanese Patent Application Laid-Open Nos. 63-180928 and 1-1.
There is a lens of Japanese Patent No. 23210. In the former case, since the front and rear negative lenses move substantially symmetrically during zooming, distortion and chromatic aberration of magnification during zooming are good, but coma cannot be removed, and the zooming range has a magnification m of -0. 64--1.42. The latter disclosed in JP-A-1-123210 seems to reduce the increase of coma at the time of zooming by asymmetrically moving both negative lenses added before and after the triplet at the time of zooming. Magnification m in the variable power range is -0.5 to-
At both ends of 2.0, distortion and chromatic aberration of magnification are conspicuous and asymmetric coma remains. Also, Japanese Patent Application Laid-Open No.
In Japanese Patent No. 34, an asymmetric negative lens is added before and after an asymmetric triplet, and the front and rear negative lenses are moved asymmetrically during zooming, and the second positive lens is moved by a very small amount during either enlargement or reduction. While moving the lens prevents the coma from increasing, the asymmetry of the amount of movement of the front and rear negative lenses is large, and distortion during magnification and chromatic aberration of magnification remain.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a copying zoom lens which has a small number of components, has little distortion in the entire zooming range, and has no asymmetric coma and chromatic aberration of magnification.

[0004]

SUMMARY OF THE INVENTION In order to solve the above problems, a copying zoom lens according to the present invention comprises a negative meniscus first lens having a concave surface facing the object side in order from the object side as shown in FIG. This is a five-element configuration including a biconvex second positive lens, a biconcave third negative lens, a biconvex fourth positive lens, and a negative meniscus fifth lens having a concave surface facing the image side, and has the same magnification (m = − 1)
In this case, the second positive lens and the fourth positive lens, and the first negative meniscus lens and the fifth negative meniscus lens are arranged symmetrically with respect to the third negative lens, respectively, so that the total lens length is minimum. The first negative meniscus lens, the fifth negative meniscus lens, and the third negative lens are displaced on the optical axis, and the entire lens system is also moved, thereby maintaining a constant object-image distance. The distance between the second positive lens is d ₂ , the distance between the second positive lens and the third negative lens is d ₄ , the distance between the third negative lens and the fourth positive lens is d ₆ , and the fourth positive lens is the fifth negative lens. The distance from the meniscus lens is d ₈ ,
The focal length of the i-th lens is f _i , the focal length of the entire system at the same magnification is f, and the change amounts of d ₂ , d ₄ , d ₆ , and d ₈ from the same magnification are Δd ₂ , Δd ₄ , When Δd ₆ , Δd ₈ and the imaging magnification are m, 1.2 <−f ₁ /f<1.6 (1) 1.2 <−f ₅ / f <1.6 (2) When −m <1 Δd ₂ > Δd ₈ > Δd ₄ > 0, Δd ₄ = −Δd ₆ · (3) −m> 1 When Δd ₈ > Δd ₂ > Δd ₆ > 0, Δd ₆ = −Δd ₄ · (4) When −m <1 1 <d ₂ / d ₈ <1.3... (5) When −m> 1 By satisfying the following conditions: 1 <d ₈ / d ₂ <1.3 (6), extremely good performance can be obtained. Wherein the first lens and the fifth lens, the second lens and the fourth lens, 1 or in the object side and the image side surface of the third lens has a minute difference in (within 5%), to the third negative lens when the magnification (m = -1),
Even when the second positive lens and the fourth positive lens, and the first negative meniscus lens and the fifth negative meniscus lens are respectively arranged substantially symmetrically, the same effects as described above can be obtained.

Conditions (1) and (2) are for improving the size of the lens system and correcting aberrations during zooming. If the lower limit is exceeded, the negative refracting power of the first lens and the fifth lens becomes excessive, so that the displacement of the lens during zooming can be reduced, which is advantageous for miniaturization of the lens, but has good aberration correction. It is disadvantageous to do so. If the upper limit is exceeded, the negative refractive power of the first lens and the fifth lens becomes too small, the displacement of the lens at the time of zooming becomes large, and the lens system becomes large. Condition (3) and condition (4) relate to the displacement of the first lens, the fifth lens, and the third lens during zooming. The aberration at the same magnification (m = -1) is advantageous because there is no distortion, asymmetric coma, or chromatic aberration of magnification when the lens system is completely symmetric. By separating the first and fifth negative lenses on both outer sides from the second to fourth core lenses as in the present invention, the focal length of the entire system is shortened,
The distance between object images during zooming can be kept constant. Distance d ₂ of the first lens and the second lens, when spread evenly spacing d ₈ of the fourth lens and the fifth lens, -m <introversive frame is increased at the time of the first reduction, -m> 1 At the time of enlargement, extroverts increase. To correct this coma aberration, -m
By setting Δd ₂ > Δd ₈ when <1 is reduced, the introverted coma is somewhat reduced, but the negative distortion and the chromatic aberration of the overcorrected magnification increase. Δd when -m> 1 is enlarged
By setting ₈ > Δd ₂ , the extravertive coma is somewhat reduced, but the positive distortion and the chromatic aberration of the undercorrected magnification increase. When the third negative lens is displaced by a small amount, coma, distortion, and chromatic aberration of magnification can be corrected. -M <
When the third negative lens is displaced toward the minute image side at the time of the reduction of 1, the introverted coma moves to the outward direction, the negative distortion moves in the (+) direction, and the chromatic aberration of the overcorrected magnification moves in the undercorrected direction.
When -m> 1, the third negative lens is displaced by a very small amount toward the object side, so that the extrovert coma is introverted, the positive distortion is in the (-) direction, and the chromatic aberration of the undercorrected magnification is overcorrected. Move in the direction of. However, the displacement of the third negative lens is smaller than the displacement of the first and fifth lenses (Δd ₂ −Δ
It is preferably at most １ ／ of d ₈ ).

The conditions (5) and (6) are for restricting the degree of asymmetry of the displacement of the first negative meniscus lens and the fifth negative meniscus lens during zooming. Condition (3)
As described in the description of the condition (4), it is preferable that the asymmetry of the displacement amount of the first negative meniscus lens and the fifth negative meniscus lens be small because the distortion and the chromatic aberration of magnification increase. When -m <1 in the condition (5), the lower limit is for a symmetrical arrangement. When the upper limit is exceeded, negative distortion and chromatic aberration of overcorrected magnification increase, and the third negative lens Cannot be corrected even by the displacement of When -m> 1 in the condition (6), the lower limit is for a symmetrical arrangement. When the upper limit is exceeded, positive distortion and chromatic aberration of insufficient correction are increased, and the displacement of the third negative lens is increased. Cannot be completely corrected.

[0007]

EXAMPLES Tables 1 to 6 show the first to third embodiments of the copying zoom lens of the present invention. The symbols are as follows. r _i : sequentially the radius of curvature of the spherical surface d _i : sequentially the thickness or air gap on the optical axis of the lens n _i : sequentially the refractive index of the lens material with respect to the d-line ν _i : the Abbe number of the lens material sequentially m : Imaging magnification (hereinafter referred to as margin)

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

FIG. 2 shows a state of displacement of each lens due to zooming of the zoom lens for copying of the present invention. The second and fourth lenses move in response to the movement of the lens for zooming, but the distance between them is kept constant. In response to this movement, the first, third, and fifth lenses move as shown with reference to the second and fourth lenses. FIGS. 3, 4 and 5 show the aberration curves of the first embodiment, FIGS. 6, 7 and 8 show the aberration curves of the second embodiment, and FIGS. 9, 10 and 11 show the aberration curves of the third embodiment. Show. In each of the embodiments, there is no asymmetric coma at the time of zooming and no chromatic aberration of magnification.
It can be seen that the distortion is small and the performance is extremely good.

[0009]

As described above, although the zoom lens for copying according to the present invention has a small number of constituent elements of five, it has good performance within the entire angle of view in the entire zoom range, and the MTF value Is also expensive. Since the distortion is as small as ± 0.1% even at the maximum value, there is an advantage that the line deviation is not conspicuous even in the case of pasting the variable-magnification copy of a map or the like.

[Brief description of the drawings]

FIG. 1 is a sectional view of a zoom lens for copying according to a first embodiment of the present invention at the same magnification (m = −1).

FIG. 2 is a diagram showing a displacement state of each lens due to zooming.

FIG. 3 is an aberration curve diagram of Example 1 when m = −1.0.

FIG. 4 is an aberration curve diagram of Example 1 when m = −0.5.

FIG. 5 is an aberration curve diagram of Example 1 when m = −2.0.

FIG. 6 is an aberration curve diagram of Example 2 when m = −1.0.

FIG. 7 is an aberration curve diagram of Example 2 when m = −0.5.

FIG. 8 is an aberration curve diagram of Example 2 when m = −2.0.

FIG. 9 is an aberration curve diagram of Example 3 when m = −1.0.

FIG. 10 is an aberration curve diagram of Example 3 when m = −0.5.

FIG. 11 is an aberration curve diagram of Example 3 when m = −2.0.

Claims (2)

(57) [Claims] 1. A negative meniscus first lens, a biconvex second positive lens, a biconcave third negative lens, a biconvex fourth positive lens, and a biconvex fourth positive lens with the concave surface facing the object side in order from the object side. This is a five-element configuration of a negative meniscus fifth lens with a concave surface. When the magnification is 1 (m = −1), the second positive lens, the fourth positive lens, and the first negative meniscus lens are used for the third negative lens. And the fifth
Negative meniscus lenses are arranged symmetrically, the overall length of the lens is minimum, and during zooming, the first negative meniscus lens, the fifth negative meniscus lens, and the third negative lens are displaced on the optical axis, and the entire lens system is displaced. The distance between the object and the image is kept constant by moving. The distance between the first negative meniscus lens and the second positive lens is d ₂ , the distance between the second positive lens and the third negative lens is d ₄ , and the third negative lens. The distance between the lens and the fourth positive lens is d ₆ , the distance between the fourth positive lens and the fifth negative meniscus lens is d ₈ , the focal length of the ith lens is f _i , and the focal length of the whole system at the same magnification is Let f be the change amounts of d ₂ , d ₄ , d ₆ , and d ₈ from the same magnification at Δd ₂ , Δd ₄ , Δd ₆ , Δ
1.2 When the d ₈ imaging magnification _{m <-f 1 /f<1.6 ··········· (1} ) 1.2 <-f 5 /f<1.6 (2) When −m <1, Δd ₂ > Δd ₈ > Δd ₄ > 0, Δd ₄ = −Δd ₆ · (3) When −m> 1, Δd ₈ > Δd ₂ > Δd ₆ > 0, Δd ₆ = −Δd ₄ · (4) When m <1, 1 <d ₂ / d ₈ <1.3 (5) − When m> 1, 1 <d ₈ / d ₂ <1.3 (6) A zoom lens for copying characterized by satisfying the following conditions: 2. A negative meniscus first lens, a biconvex second positive lens, a biconcave third negative lens, a biconvex fourth positive lens, and a biconvex fourth positive lens with the concave surface facing the object side in order from the object side. The fifth lens has a negative meniscus fifth lens with a concave surface, and one or more of the first lens and the fifth lens, the second lens and the fourth lens, and at least one of the object-side and image-side surfaces of the third lens are minute. (Within 5%), and at the same magnification (m = -1), the second positive lens and the fourth positive lens, and the first negative meniscus lens and the fifth negative meniscus lens with respect to the third negative lens. Are arranged substantially symmetrically, the total length of the lens system is minimum, and during zooming, the first negative meniscus lens, the fifth negative meniscus lens, and the third negative lens are displaced on the optical axis, and the entire lens system is also displaced. The first negative meniscus is to keep the distance between objects and images constant by moving The distance between the lens and the second positive lens is d ₂ , the distance between the second positive lens and the third negative lens is d ₄ , the distance between the third negative lens and the fourth positive lens is d ₆ , and the distance between the fourth positive lens and the fourth positive lens is d ₆ . 5 The distance from the negative meniscus lens is d ₈ , the focal length of the i-th lens is f _i , and the focal length of the entire system at the same magnification is f, and d ₂ , d ₄ , d ₆ , and d ₈ from the same magnification. Assuming that the amounts of change are Δd ₂ , Δd ₄ , Δd ₆ , and Δd ₈ , respectively, 1.2 <−f ₁ /f<1.6 (1) 1.2 <− f ₅ /f<1.6 (2) When −m <1 Δd ₂ > Δd ₈ > Δd ₄ > 0, Δd ₄ = −Δd ₆ · (3) − When m> 1, Δd ₈ > Δd ₂ > Δd ₆ > 0, Δd ₆ = −Δd ₄ · (4) When −m <1, 1 <d ₂ / d ₈ <1.3,... ···· (5) -m> 1 when _{1 <d 8 / d 2 <} 1.3 ······· (6) A copying zoom lens characterized by satisfying the following conditions.