JPH0533367B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical field of the invention) The present invention includes a wide angle of view with a maximum angle of view exceeding 60°,
The present invention relates to a high variable power zoom lens having a relatively wide variable power range from wide-angle to telephoto. (Background of the Invention) In recent years, various zoom lenses of this type for use with 35 mm still cameras have been proposed, but there is a trend toward increasingly higher zoom ratios. In the present invention, = about 35 to 200,
Although the objective was to achieve a high zoom ratio with a zoom ratio of around 5.7x, it was quite difficult to combine such a high zoom range, including a wide angle, into a single lens. First, in order to achieve a high zoom ratio while including a wide angle, the front lens focusing group must be composed of a positive group.
Therefore, as a disadvantage of positive focusing group,
There are two problems: the close distance cannot be made very short, and the fluctuation of aberrations associated with short distance focusing (hereinafter simply referred to as short distance fluctuation) is large. It is possible to shorten the close distance to some extent by increasing the diameter of the front lens or shortening the focal length of the front lens, but in that case, you have to sacrifice the size of the lens and the fluctuation and reduction of aberrations. You won't get any more. In addition, in order to realize a high variable magnification zoom lens with a relatively small lens system, the power of each variable magnification must be increased, but this will reduce spherical aberration corresponding to the minimum F number at the telephoto end. This worsens, and the fluctuations in various aberrations during zooming (hereinafter simply referred to as fluctuations in magnification) become larger.
The ways in which change occurs will also become more complex. For example, the fluctuation of the meridional image plane at 15 mm, which generally corresponds to 70% of the image height, is negative at =35, positive at =50, 0 at =85,
It exhibits an inverted S-shaped movement, negative at =135 and 0 at =200. Regarding spherical aberration, at the aperture value of 70%, it becomes significantly negative at =35, slightly negative at =50,
=85 is 0, =135 is positive, =200 is negative,
It shows an S-shaped movement. Therefore, there are some places in the variable power range where the image surface is difficult to match the spherical aberration.
In particular, in the vicinity of =50 and =135, the spherical aberration and the peripheral image plane will be largely shifted, so it is difficult to always obtain a flat image over the entire magnification range. (Objective of the Invention) The object of the present invention is to provide a high-power zoom lens that has a high magnification including a wide angle of view, is compact, and has excellent imaging performance over the entire zoom range. be. (Summary of the Invention) As shown in the basic configuration diagram of FIG. 1, the zoom lens according to the present invention includes, in order from the object side, a first lens group G with a positive refractive power, a second lens group G ₂ with a negative refractive power _. ,
It has a third lens group _G3 with positive refractive power, and these three
The two lens groups as a whole are configured to be almost afocal, and there is also a fourth lens group _G4 with positive refractive power on the image plane I side of these groups, so that when zooming from the wide-angle end _W to the telephoto end _T , the first lens group
G ₁ and the fourth lens group G ₄ monotonically move by almost the same amount toward the object side, and the third lens group G ₃ moves toward the object side at a rate of about 0.4 to 0.8 of the movement of the first lens group G ₁ . At the same time, the second lens group _G2 is configured to move toward the object side at least near the wide-angle end. In this basic configuration, as shown in Japanese Unexamined Patent Application Publication No. 58-78114 filed by the same applicant as the present application, the second lens group is moved toward the object side near the wide-angle end. This has the effect of bringing the oblique light beam in the intermediate state closer to the center of the lens, and it is possible to reduce the diameter of the front lens. In addition, in such a zooming method, the entire lens system moves to change the magnification, which places strict demands on the precision of the lens barrel structure. It is also advantageous in terms of aberration correction because it is possible to increase the telephoto ratio at the telephoto end while maintaining a compact structure at the wide-angle end. In the basic configuration as described above, in the present invention,
In order to support a high variable zoom of about 5.7x,
Regarding the focal length ₁ of _the first lens group and the focal length ₂ of the second lens group, it is necessary to satisfy the following condition: 4.5< _1/2 <6.5 (1). In this case, the focal length ₁ of the first lens group is configured to be relatively short compared to the focal length at the telephoto end of the entire system, aiming at miniaturization, which worsens short-range fluctuations and magnification fluctuations. , fluctuations in both are suppressed by making the focal length ₂ of the second lens group a little longer. If the upper limit is exceeded, the size will become too large, and if the lower limit is not met, short-range fluctuation,
Both magnification fluctuations worsen. As long as the condition of equation (1) is met, it is possible to obtain a compact lens with small aberration fluctuations. In such a basic configuration of the present invention, it is desirable that the specific configuration of each lens group is as follows. That is, for example, as shown in FIG. 2, the first lens group G ₁ includes a positive first lens component L 1 consisting of a negative meniscus lens and a biconvex positive lens, and a positive meniscus lens component L ₁ with a convex surface facing the object side. The second lens group _G2 includes, in order from the object side, a third lens component _L3 , which is a negative meniscus lens with a convex surface facing the object side, and a fourth lens component _L4 , which is a bonded negative lens component _. , the fifth lens component of the negative lens, which is made of laminated material and has a surface with a stronger curvature facing the object side.
L ₅ , and the third lens group G ₃ includes, in order from the object side, a sixth lens component L ₆ which is a positive lens with a surface with a stronger curvature facing toward the image side, a seventh lens component L ₇ which is a biconvex positive lens,
It is desirable to have an eighth lens component _L8 of a negative meniscus lens with a convex surface facing the image side. In addition, the fourth lens group G ₄ is the ninth lens component of a biconvex positive lens.
L ₉ , 10th lens component L ₁₀ of a positive lens with a surface with stronger curvature facing toward the object side, 11th lens component L ₁₁ of a biconcave lens with a surface with stronger curvature facing toward the image side, surface with stronger curvature toward the image side It is desirable to have a twelfth lens component L ₁₂ which is a positive lens with a convex surface facing the image side, and a thirteenth lens component L ₁₃ which is a positive lens made of a combination of a biconvex positive lens and a negative meniscus lens with a convex surface facing the image side.
Note that by further providing a bonding surface on the lens component in each lens group, aberrations can be corrected more favorably. In the present invention, in order to further correct magnification fluctuations in aberrations, the refractive index of each positive lens and negative lens forming the fourth lens component _L4 as a bonded negative lens in the second lens group _G2 is When n ₅ and n ₆ are expressed as n 5 and n 6 , it is desirable to satisfy the following conditions: n ₅ > 1.8 n ₆ > 1.8. If this condition is not met, fluctuations in comatic aberration and fluctuations in the image plane during zooming will become large, making it difficult to correct aberrations with a simple configuration. Also, when the telephoto focal length is 200mm,
As the secondary spectrum of colors becomes larger, it becomes necessary to introduce anomalous dispersion glass. Therefore, by increasing the radius of curvature of the bonding surface of the first lens component _L1 ,
In order to keep the center thickness of the laminated lens small,
When the Atsube number of the positive lens forming the first lens component L ₁ of this lamination is ν ₂ , it is desirable to introduce an anomalous dispersion glass that satisfies the condition of 80<ν ₂ (3). Color blur on the telephoto side can be drastically reduced. If the condition of formula (3) is not satisfied,
Chromatic aberration on the telephoto side cannot be removed and image performance deteriorates. In addition, in order to satisfactorily correct spherical aberration throughout the entire zoom range, especially at the telephoto end, the shape factor of the sixth lens component L ₆ located closest to the object side of the third lens group G ₃ must be set to q ₆ When , it is desirable to satisfy the following condition: −3.6<q ₆ <−0.5 (4). However, the shape factor q is defined as q=r _b + _ra /r _{b −ra} , where ra and rb are the curvature radii of the object-side and image-side lens surfaces of the lens. When the upper limit of this range is exceeded, the spherical aberration becomes more positive, resulting in image quality with a lot of flare. If the lower limit is not met, at the wide-angle end, the aperture ratio will increase toward the negative side as the aperture ratio increases from 70% to 100%, which will deviate from the full collection shape, and at the telephoto end, the curvature toward the negative side will become stronger. This is inconvenient because it moves further to the negative side when it comes to a short-distance focusing state. Furthermore, in order to maintain a good coma aberration balance when the focal lengths of the entire system are =35 and =50, the 10th lens component _L10 and the 11th lens component L10 in the 4th lens group _G4 must be When the ₁₁ shape factors are respectively q ₁₀ and q ₁₁ , it is desirable to satisfy the following conditions: 0.5<q ₁₀ <5 (5) -1<q ₁₁ <0.0 (6). If the upper limit of equations (5) and (6) is exceeded, the tendency will be for the inner frame, and if the lower limit is not met, the tendency will be for the outer frame. In particular, 70% of the frames around =35 are likely to be inside frames, 70% of the frames around =50 are likely to be outside frames, and 70% of the frames around =135 are likely to be inside frames. (Example) Next, an example of the present invention will be described. Both embodiments of the present invention are zoom lenses for 35 mm still cameras, having a focal length of 35 to 200 mm, a zoom ratio of 5.7, and an F number of approximately 3.5. The first embodiment, as shown in FIG. 2, has the lens configuration described above. Further, the lens configuration of the second embodiment differs from that shown in FIG. 3 in that the frontmost positive lens component _L9 in the fourth lens group _G4 is bonded together for achromatic purposes. Tables 1 and 2 below show the specifications of the first to third embodiments, respectively. In each table, each value is shown sequentially from the object side, and the subscript number represents the order from the object side. Various aberration diagrams of the first and second embodiments are shown in FIGS. 4 and 5, respectively. In each aberration diagram, A represents the wide-angle end _W , B represents the intermediate state _M , and C represents the telephoto end _T. In each state, spherical aberration Sph, astigmatism Ast, distortion aberration Dis, and coma aberration are shown.
Coma is shown, and the amount of violation of the sine condition is also shown with a dotted line in the spherical aberration diagram. Figure 6 also shows how the magnification of the meridional image surface changes at 15 mm from the optical axis, which corresponds to 70% of the image height (solid line), and how the spherical aberration changes with magnification at an aperture of 70% (dotted line). )showed that. Curves 1a and 1b
curves 2a and 2b represent the magnification variations of the meridional image surface and spherical aberration of the first embodiment, and curves 2a and 2b represent those of the second embodiment.

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[Table] Each is shown. As shown in the figure, in each example, the meridional image surface changes in an inverted S-shape, and the spherical aberration changes in an S-shape, but both are sufficiently well balanced for practical use. (Effects of the Invention) As described above, according to the present invention, various aberrations are suppressed over the entire magnification range while having a wide angle of view of 64° at the maximum and a high zoom ratio of 5.7. This makes it possible to create a compact zoom lens that is compensated for.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the movement locus of each lens group for zooming the zoom lens according to the present invention, FIG. 2 is a lens configuration diagram of the first embodiment, and FIG. 3 is a lens configuration diagram of the second embodiment. , Figures 4 and 5 are respectively 1st and 5th.
Various aberration diagrams of the second embodiment, FIG. 6 are diagrams showing how the meridional image surface and spherical aberration of each embodiment change due to zooming. [Explanation of symbols of main parts], G ₁ ... first lens group, G ₂ ... second lens group, G ₃ ... third lens group,
G ₄ ...Fourth lens group.

Claims (1)

[Claims] 1. A first lens group having positive refractive power in order from the object side,
It has a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group with positive refractive power, and when zooming from the wide-angle end to the telephoto end, the first lens group and the The fourth lens group moves monotonically by almost the same amount toward the object side, and at the same time, the third lens group moves by 0.4 to 0.8 with respect to the amount of movement of the first and fourth lens groups.
The second lens group is configured to move monotonically toward the object side with twice the amount of movement, and the second lens group also moves toward the object side at least near the wide-angle end, and the first lens group is a negative meniscus lens and a negative meniscus lens. It has a first lens component that is a positive lens that is laminated with a convex positive lens, and a second lens component that is a positive meniscus lens that has a convex surface facing the object side, and the second lens group is arranged in order from the object side toward the object side. It has a third lens component of a negative meniscus lens with a convex surface, a fourth lens component of a bonded negative lens, and a fifth lens component of a bonded negative lens, and the third lens group has a curvature increasing from the object side to the image side. A sixth lens component of a positive lens with a strong surface facing, a seventh lens component of a biconvex positive lens,
It has an eighth lens component of a negative meniscus lens with a convex surface facing the image side, and the focal length of the first lens group is
f ₁ , the focal length of the second lens group is f ₂ , the Atsube number of the positive lens forming the first lens component is ν ₂ , the fourth lens of the bonded negative lens in the second lens group
When _the refractive index of each of the positive lens and negative lens forming the lens component is _n5.n6 , and the shape factor of the sixth lens component located closest to the object side of the third lens group is _q6 , then 4.5 ＜f ₁ /f ₂ ＜6.5 …(1) n ₅ ＞1.8, n ₆ ＞1.8 …(2) 80＜ν ₂ …(3) −3.6＜q ₆ ＜−0.5 …(4) (However, shape The factor q is the radius of curvature of the object side and image side lens surfaces of the lens, ra and rb.
A high variable magnification zoom lens including a wide angle of view, characterized in that it satisfies the following condition: q=(rb+ra)/(rb-ra).