JPS6144289B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a zoom lens with a large zoom ratio suitable for use in a 35 mm still camera. A zoom lens has the advantage of being able to freely change the size of the subject while keeping the camera fixed. In other words, the subject can be immediately changed to an optimal size and photographed according to the photographer's intention. So 8
For mm cameras, 5x to 10x zoom lenses are commonly used, and for TV cameras, 10x to 30x zoom lenses are commonly used. However, compared to an 8mm camera or TV camera that has a small screen size and shoots videos, a still camera that has a large screen size and takes still images requires higher optical performance. In order to realize a zoom lens with a very high magnification ratio, there was a big problem in correcting aberrations. The present invention has a film size of 50mm when using a 35mm film size.
The objective of the present invention is to provide a high-performance zoom lens with a high magnification ratio ranging from a standard lens of about 300 mm to a super telephoto lens of about 300 mm, and whose total length (from the first surface to the film surface) is shorter than the focal length at the telephoto end. There are two ways to reduce the size of a zoom lens: one is to shorten the variable power section, and the other is to shorten the relay section. Although the latter method has the advantage of suppressing aberration fluctuations due to zooming, the configuration of the relay section is limited to a telephoto type, making it difficult to correct aberrations throughout the entire system. The former method, on the other hand, has a problem in that aberration fluctuations caused by the zooming section increase as a result of zooming. In the former method, the present invention has successfully suppressed aberration fluctuations and achieved miniaturization. On the other hand, aberration fluctuations during zooming become a particular problem when realizing a high-performance zoom lens, and the larger the zoom ratio and the smaller the lens, the more they occur. The reason for this is that in order to make the lens more compact, the power of each lens group of the zoom lens is increased, which increases the amount of aberration in each lens group, and when changing the magnification, the aberration correction becomes unbalanced and aberration fluctuations increase. Among the lens groups, the movable lens group having a variable power function has the strongest power and moves the most, so it has the greatest effect on aberration fluctuations associated with variable power. In order to realize a zoom lens with a high magnification ratio and high performance, the present invention solves the above problems by providing a movable lens group with a variable magnification function with an appropriate lens arrangement and lens shape as shown below. It is something. The present invention consists of a positive lens group, a negative lens group, a positive lens group, and a negative lens group in this order.The lens group has a focusing function, and the lens group focuses on the optical axis. The lens group has the function of moving and changing the magnification, and the lens group has the function of always keeping the image plane position constant by reciprocating movement linked to the movement of the lens group. , is a so-called relay lens, and the first lens group includes, in order, a negative meniscus lens with a convex surface facing forward (object side), a bonded lens consisting of a biconcave and a biconvex lens, and a negative lens with a strongly concave surface facing forward. , the focal length of the bonded lens in the 1st lens group is _F2 , the radius of curvature of the i-th lens surface in the 1st lens group is Ri, and the focal length at the wide-angle end of the entire system is Fω, the following conditions are satisfied: do. (1) -0.1/Fω<1/ _F2 <0 (2) 1.1Fω< _R4 <1.5Fω (3) 0.65< _R6 / _R3 <1.0 Next, we will explain the meaning of setting each condition. . If the power of the 1st lens group is strengthened in order to achieve a large magnification ratio and to reduce the size of the variable power section, large aberration fluctuations will occur due to the change in magnification. , the power is divided by forming the third lens group into three groups, but if the power is divided into equal parts, a large amount of negative distortion will occur on the wide-angle focal length side, so condition (1) is important. When the lower limit is exceeded, negative distortion becomes significant on the wide-angle focal length side, and when the upper limit is exceeded, the meaning of dividing the power is lost and aberration fluctuations accompanying zooming become large. The bonded surface in the second lens group contributes to the correction of spherical aberration and longitudinal chromatic aberration, but if the curvature becomes too strong, inner coma aberration and high-order aberration will occur on the wide-angle focal length side. Since chromatic aberration of magnification occurs, condition (2) is set. If the upper limit is exceeded, it becomes difficult to correct spherical aberration and longitudinal chromatic aberration, and if the lower limit is exceeded, inner coma aberration and high-order chromatic aberration of magnification will significantly occur on the wide-angle focal length side. Furthermore, by appropriately distributing power within the lens group, it is possible to appropriately correct spherical aberration, which tends to be overcorrected on the telephoto focal length side, which is achieved by condition (3). If the upper limit of condition (3) is exceeded, spherical aberration will be significantly overcorrected on the telephoto focal length side, and if the lower limit is exceeded, aberration fluctuations in comatic aberration and lateral chromatic aberration due to zooming will become significant. In addition to appropriately selecting the configuration of the first lens group, in order to suppress fluctuations in aberrations associated with zooming, the method of movement of the first lens group in conjunction with the movement of the first lens group on the optical axis during zooming is necessary. Although it is a well-known technique because it is important, I will add it just in case. If the position of the first lens group with respect to the image plane formed by the first lens group is optically conjugate to each other at the wide-angle end and the telephoto end of the focal length, the movement of the image plane due to the movement of the first lens group can be made into the same image. The way the first lens group moves to correct the surface is to have one inflection point and draw a smooth curve convex to the object side.
The position is the same at the wide-angle end and the telephoto end of the focal length. This example is characterized in that it is configured such that the focal length at the telephoto end is obtained before the first lens group moves to a position optically conjugate with the focal length at the wide-angle end. The magnification change due to only the 1st lens group is -1/Mmin to -Mmax considering from the wide-angle focal length side
(However, when changing to 0<1/Mmin<Mmax), by satisfying the condition (a) 0.5<Mmax/Mmin<0.8, fluctuations in spherical aberration due to zooming can be suppressed to a small value. Condition (a)
When the upper limit is exceeded, fluctuations in spherical aberration become large, and when the lower limit is exceeded, the power of each lens group becomes strong and various aberration fluctuations become large. As mentioned above, the third lens group with variable power function is shaped appropriately,
In addition, by appropriately moving the 1st lens group, the amount of aberration variation due to zooming can be kept small. It is possible to appropriately correct aberrations unrelated to Next, in a zoom lens that adopts the configuration of the first lens group described above, the first lens group includes a negative bonded lens with a concave surface facing forward, a positive meniscus lens with a convex surface facing forward, and a positive meniscus lens with a convex surface facing forward, and a rear (image A negative meniscus lens with a concave side facing toward the side) and a bonded positive lens with a bonded surface facing concave toward the rear, and in the lens group, the radius of curvature of the jth lens surface is Rj, The thickness or air gap of the jth lens is Dj, and the refractive index of the jth lens is N.
j, and when the Abbe number of the j-th lens is νj, it is desirable to satisfy the following conditions. _{( 4 ) 0.4 Fω _ _} 0.25Fω (8) 0.035/Fω<|N ₆ −N ₅ |/R ₉
<0.065/Fω, however, N ₆ <N ₅ (9) 25 < ν ₆ - ν ₅ As a result, both aberration fluctuations associated with zooming occurring in the th to th lens groups and aberrations unrelated to zooming, A high-performance zoom lens with a large zoom ratio that is well-corrected can be realized. Next, each condition will be explained. Among the lens groups, on the wide-angle focal length side, the central light beam passes through the positive power lens group with a diameter close to the effective diameter, and on the telephoto focal length side, the central light beam passes through the positive power lens group and the positive power lens group. The central light beam passes through the lens group with a diameter close to the effective diameter. On the other hand, for the lens group having negative power, the central light beam does not have a diameter close to the effective diameter. As a result, even if the chromatic aberrations in each lens group are completely corrected, the spherical aberrations at short wavelengths in the central light beam incident on the first lens group are significantly overcorrected. Condition (4) is for correcting short wavelength spherical aberration, and if the upper limit is exceeded, correction becomes difficult, and if the lower limit is exceeded, short wavelength spherical aberration becomes undercorrected. The third group in the first lens group has a diverging effect,
When a positive power is imparted to the bonded surfaces, the first surface of the first group has a strongly concave surface in order to correct the aberrations generated at the bonded surfaces, resulting in higher-order spherical aberration. In other words, a significant sagittal halo occurs.
Condition (5) is for effectively correcting short wavelength spherical aberration without generating a sagittal halo.
Condition (6) is for correcting spherical aberration and astigmatism that cannot be corrected by the first lens group, and if the upper limit is exceeded, it becomes difficult to correct spherical aberration and astigmatism, so the lower limit is If it exceeds this, it will be over-corrected and the total length will become longer. Distortion that could not be corrected by the 1st to 3rd lens groups is corrected by the positive lens of the 4th group in the 4th group, but condition (7) is necessary to correct the distortion, and if the upper limit is exceeded, coma aberration occurs. In addition to this, the overall length becomes long, and if the lower limit is exceeded, the distortion of the pincushion becomes significant at the telephoto focal length side. Condition (8) is for correcting field curvature, and when the upper limit is exceeded, over-correction occurs, and when the lower limit is exceeded, under-correction becomes significant. Condition (9) is for correcting lateral chromatic aberration, and if the lower limit is exceeded, the correction will be significantly insufficient. The above has described the aberration fluctuations associated with zooming and the conditions for aberration correction that are not caused by zooming.Next, we will discuss aberration fluctuations during focusing.
However, these are standards commonly employed by lens designers. Aberration fluctuations due to focusing are most problematic at the telephoto end focal length. By optimizing the lens shape of the first lens group, aberration fluctuations, particularly spherical aberration fluctuations, can be suppressed to a small level. Furthermore, even if the performance of the reference wavelength is good on the telephoto side, if chromatic aberration is large, high performance cannot be obtained, so it is necessary to keep the correction of chromatic aberration particularly small on the long focal length side. On the long focal point side, the beam diameter is maximum in the first lens group, so
Correction in the first lens group is effective. Therefore,
In the 1st lens group, in order from the front, there is a laminated biconvex lens with a laminated surface facing forward with a convexity, and a positive lens with a strong convexity facing forward, and in the 1st lens group, the curvature of the kth lens The radius is Rk, the kth
When the refractive index of the th lens is Nk and the Atsube number of the k th lens is νk, (b) 0.30<|R ₄ /R ₃ |<0.38 (c) −0.05/Fω<1/R ₅ <0.05/Fω (d) 40<ν ₂ −ν ₁ (e) 0.25<N ₁ −N ₂ The conditions are effective for aberration fluctuations due to focusing and chromatic aberration on the telephoto side. Conditions (b) and (c) are intended to keep aberration fluctuations due to focusing small; if both exceed their upper limits, aberration fluctuations due to focusing will increase, and performance for close objects will deteriorate, especially on the telephoto side. If the lower limit is exceeded, comatic aberration and distortion on the telephoto side become significant, and correction becomes difficult in the lens system below the 1st lens group. Condition (d) is to correct chromatic aberration at the telephoto end, and if the lower limit is exceeded, chromatic aberration will cause
Performance at the telephoto end is significantly degraded. Condition (e) is for correcting spherical aberration and coma aberration on the telephoto side in a well-balanced manner, and if the lower limit is exceeded, coma aberration will occur significantly. In order to realize conditions (d) and (e), it is effective to use special glass with a low refractive index and low dispersion. The present invention has succeeded in improving the optical performance on the telephoto side, which is a problem with large zoom ratios, by using this special glass for the second glass in the first group, which is most effective in zoom lens systems. Next, examples according to the present invention will be described. The lens cross-sectional shapes of Examples 1 and 2 are shown in FIGS. 1 and 2, and the spherical aberration, astigmatism, and distortion of Examples 1, 2, 3, and 4 are Aberrations and chromatic aberrations of magnification are shown in Figure 3 a, b, c~
Shown in Figures 6a, b, and c. In FIGS. 3 to 6, a is an aberration diagram at the wide-angle end focal length, b is an intermediate focal length, and c is an aberration diagram at the telephoto end focal length. In the numerical examples, ri is the radius of curvature of the lens surface, di is the lens thickness or air gap, and Nd is d.
The refractive index for the line, νd, is the Abbe number for the d line. Also, the third-order aberration coefficient is 1 when the focal length at the wide-angle end is
This is the value when normalized to .

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【table】 [Brief explanation of the drawing]

FIG. 1 is a sectional view of the lens of Example 1. FIG. 2 is a sectional view of the lens of Example 2. FIGS. 3a, b, and c are longitudinal aberration curve diagrams for an object at infinity at the wide-angle, intermediate, and telephoto ends of Example 1. FIGS. 4a, b, and c are longitudinal aberration curve diagrams of Example 2. Figure 5 a, b, and c are Example 3
A longitudinal aberration curve diagram of . FIGS. 6a, b, and c are longitudinal aberration curve diagrams of Example 4. In the figure, ri is the radius of curvature of the lens surface.
di is the lens thickness or air gap, d is the d-line aberration curve, g is the g-line aberration curve, ΔM is the meridional image surface, and ΔS is the sagittal image surface.

Claims (1)

[Claims] 1. In a zoom lens in which a positive first lens group, a negative first lens group, a positive first lens group, and a negative first lens group are arranged in order, the first lens group has a focusing function. However, the first lens group has a function of changing magnification by moving on the optical axis, and the second lens group makes reciprocating motion to correct the movement of the image plane due to the movement of the first lens group. consists of a negative meniscus lens with a convex surface facing forward, a laminated lens consisting of biconcave and biconvex lenses, and a negative lens with a strongly concave surface facing forward, and the focal length of the laminated lens of the first lens group is _F2 , the radius of curvature Ri of the i-th lens surface in the lens group,
When the focal length of the entire system at the wide-angle end is Fω, (1) −0.1/Fω<1/F ₂ <0 (2) 1.1Fω<R ₄ <1.5Fω (3) 0.65<R ₆ /R A zoom lens characterized by satisfying each of the following conditions: ₃ <1.0. 2. In a zoom lens in which a positive lens group, a negative lens group, a positive lens group, and a negative lens group are arranged in order, the first lens group has a focusing function, and the third lens group has a focusing function. It has the function of changing magnification by moving on the optical axis, and the first lens group makes reciprocating motion to correct the movement of the image plane due to the movement of the first lens group, and the first lens group convexes forward in order. The group includes a negative meniscus lens with a concave surface facing forward, a laminated lens consisting of a biconcave and a biconvex lens, and a negative lens with a strongly concave surface facing forward; It has a positive meniscus lens with a convex side facing forward, a negative meniscus lens with a concave side facing backward, and a bonded positive lens with a bonded surface facing concave backward, and the focal length of the bonded lens in the first lens group is F. _2. The radius of curvature of the i-th lens surface in the lens group is Ri, the radius of curvature of the j-th lens surface in the lens group is Rj, the thickness or air gap of the j-th lens is Dj, and the j-th lens surface is Dj. The refractive index of the th lens is Nj, the Atsube number of the jth lens is νj,
When the focal length of the entire system at the wide-angle end is Fω, (1) −0.1/Fω<1/F ₂ <0 (2) 1.1Fω<R ₄ <1.5Fω (3) 0.65<R ₆ /R ₃ ＜1.0 (4) 0.4Fω＜｜R ₂ ｜＜0.5Fω, however, R ₂
<0 (5) N ₂ -N ₁ <0.05 (6) 0.9<R ₇ /R ₄ <1.3 (7) 0.14Fω<D ₇ <0.25Fω (8) 0.035/Fω<|N ₆ -N ₅ |/R ₉
A zoom lens characterized by satisfying the following conditions: <0.065/Fω, provided that N ₆ <N ₅ (9) 25 < ν ₆ - ν ₅ .