JPH0115841B2 - - Google Patents

Description

[Detailed description of the invention]

This invention is a so-called two-component zoom lens system consisting of a negative front lens component and a positive rear lens component, and has an aperture ratio of about F3.5 and a variable magnification angle of view ranging from 76° to 46°. This paper relates to the improvement of an ultra-wide-angle zoom system that is compact and has a simple configuration with a ratio of around 1.7. In recent years, many zoom lenses with a two-component configuration that have a positive lens-first four-element front negative lens component have been announced with a more compact shape or a simpler configuration. . However, the requirements for brightness, simple construction, and wide angle of view have not yet been fully satisfied. For example, both the front and rear components are composed of four elements, and the shape is relatively compact, but the zoom ratio is about 1.8.
The aperture ratio is F3.5 to F4.5, the angle of view is relatively narrow from 62° to 35° (Japanese Patent Application Laid-open No. 52-152250), and both the front and rear components have 4 elements, the zoom ratio is 2.7, and the angle of view is 76°. Although it has a wide angle of 31 degrees, it has an aperture ratio of F3.5 to F4.5 and is large in size (Japanese Patent Laid-Open No. 140047/1983). Also, the angle of view
A relatively small lens with a zoom ratio of around 1.7 that covers 76 degrees has a lens configuration of 9 to 10 elements. (Japanese Unexamined Patent Publication No. 52-152250, Patent Application No. 53-152886, same
54-43592, etc.) In this type of lens system, in order to make the shape compact, it is necessary to strengthen the refractive power of both the front negative lens component and the rear positive lens component, and at the same time reduce the combined thickness of each component. be. However, if the front negative lens component has a large refractive power and has a small number of components, and is made smaller, the occurrence of higher-order aberrations such as spherical aberration, field curvature, and distortion becomes large as a negative lens system. This makes it difficult to make the zoom system have a large aperture, especially on the long focal length side, and to make it wide-angle. Similarly to the front negative lens component, higher-order aberrations occur significantly in the rear positive lens component. In addition, if the focal length of the front negative lens component is small relative to the focal length range of the zoom system, the image magnification applied by the rear lens (virtual image a by the front negative lens component and image formed by the rear positive lens component) Real image-b
The magnification |b/a|) becomes large, which makes it difficult to correct aberrations as a rear positive lens component even if the zoom ratio is the same. The reason why each of the zoom lenses described above has not been able to achieve sufficient results is because of such difficulties in correcting aberrations. This invention aims to make a two-component zoom lens system compact and simple in construction, consisting of a front negative lens component preceded by a positive lens and a rear positive lens component of positive, negative, positive. In order to strengthen the effect of the positive lens that cancels out the negative power, the power of the lens _L1 is given to be relatively large relative to the lens _L4 so that the residual aberration is small even if the shape is small. The rear lens component is a negative lens L ₇
The rear positive lens _L8 is constructed as symmetrically as possible with respect to the front two positive lenses _L5 and _L6 . This is an attempt to suppress changes in aberration due to large differences in image magnification in the rear positive lens component. A wide-angle zoom lens system having the features of the present invention as described above is composed of a front lens component having a negative focal length from the object side and a rear lens component having a positive focal length. In a zoom lens system, the focal position is fixed at a constant position in the image field while changing the focal length of the entire lens system by moving the rear lens components in the optical axis direction. Positive lens sequentially from
L ₁ , negative lenses L ₂ , L ₃ with strong concave surfaces facing the image side,
It consists of four single lenses, a positive meniscus lens L ₄ with a convex surface facing the object side, and the rear lens component consists of a biconvex positive lens L ₅ sequentially from the object side, and a positive meniscus lens L ₆ with a strong convex surface facing the object side. , consisting of four single lenses: a biconcave negative lens L ₇ and a positive lens L ₈ .
It consists of a total of eight single lenses at the front and rear, and the combined focal length of the entire zoom system on the short focal length side is f _W , the focal length of the front negative lens component is f _Fc , the focal length of the rear positive lens component is f _Rc , and the front lens component Σd _Fc is the sum of the lens thickness and air distance of the rear lens component, Σd _Rc is the sum of the lens thickness and air distance of the rear lens component, and each lens L ₁ sequentially from the object side.
The individual focal length of ~ _L8 is _f1 ~ _f8 , the composite focal length of lens _L5L6 is _f5,6 , the sum of _the lens thickness and air gap of lenses _L5 ~ _L7 is d9 _~12 , Thickness of lens L ₈
d ₁₅ , and when n ₈ is the refractive index at the d-line of the glass material of L ₈ , 1.6<|f _Fc /f _W |<1.8 (1) 0.34<|Σd _Fc /f _Fc |<0.41 (2- 1) 1.05＜Σd _Rc ／Σd _Fc ＜1.30 (2-2) 1.8＜f ₁ /f ₄ ＜2.1 (3) 0.75＜f _5,6 /f ₈ ＜0.95 (4) 0.32＜d _9〜12 /f It is characterized by satisfying the following conditions: _Rc <0.41 (5-1) 0.14<d ₁₅ /f _Rc <0.21 (5-2) 1.7<n ₈ (6). Among these conditions, (1) and (2) are the basic conditions for achieving a compact shape, and when the zoom ratio is around 1.7 as in this invention, the composite focal length on the long focal length side Let f _T be f _W = 1, then
f _T =1.7. The above |b/a| is |synthetic focal length f/f _Fc |, so by (1), f _Fc is −1.7
If it is close, the combined focal length is |b/a| Short focal length 1 1/1.7 Long focal length 1.7 1.7/1.7, and the image magnification due to the rear positive lens component is 1/1.7
and 1. If the lower limit of (1) is exceeded and becomes smaller than 1.6, it may be difficult to correct the aberration of the front lens component due to the fact that the thickness Σd _Fc of the front negative lens component was set small in (2-1). Under the above-described image magnification conditions, it becomes difficult to correct aberrations in the rear lens component with only four lenses. On the other hand, when the upper limit is exceeded, aberration correction is easy and (2
In relation to setting the thickness Σd _Rc of the rear lens component relatively small in -2), the total length including the back focus f _B becomes shorter over the entire focal length, but at the short focal length side, the predetermined f Securing _B will be difficult. Furthermore, the diameter of the front surface of the lens becomes large due to the need to maintain the incident light beam at a wide angle, which becomes an obstacle to compactness. Condition (2) regulates the thickness of each front and rear lens component, and (2-1) is also related to (1) and is an essential condition for making the shape compact. (2-1) (2-2) Both upper limits are the limit values for achieving miniaturization; on the other hand, exceeding the lower limit not only makes it difficult to correct aberrations, but also widens the range in the case of (2-1). It is difficult to secure the luminous flux at the viewing angle, (2-2)
In this case, it becomes difficult to secure a luminous flux that fills the aperture. Condition (3) is to keep f ₁ / f ₄ relatively small, effectively utilize the action of the positive lens in the front negative lens component, and eliminate spherical aberration and coma aberration caused by the compact yet quite large negative power. This is intended to cancel distortion, etc., and the upper limit is the limit value at which this effect occurs; if f ₁ becomes too small beyond the lower limit, the convergence effect in the wide-angle area is large and high-order distortion occurs. becomes larger, or it becomes necessary to increase the diameter of the front lens. Conditions (4), (5), and (6) are conditions regarding the rear lens component.
Condition (4) is the two positive lenses L ₅ in front of the negative lens L ₇ ,
It regulates the power ratio between L ₆ and the single positive lens L ₈ on the rear side, and has a relatively large value compared to conventionally known ones. The conventional type directly receives the diverging light beam from the front negative lens component, so the front positive lenses L ₅ and L ₆ are given larger positive power than the rear positive lens, and for this reason, the aforementioned rear lens component On the side where the image magnification b/a is larger, that is, on the long focus side, convergent coma aberration occurs on the front side, and divergent coma aberration occurs on the rear side (both in the direction of increasing the image). It was big. This tendency becomes even more noticeable as each lens configuration becomes simpler. Condition (4) attempts to make the front and rear positive powers nearly symmetrical in order to reduce this adverse effect. The lower limit is a limit value for not losing this effect, and if the upper limit is exceeded, distortion in the negative direction will increase. Condition (5) regulates the thickness of the positive power portion in the rear lens component, but in order to obtain the same effect as condition (4), compare the value of (5-2) with the known one. Furthermore, the value of (5-1) is also set relatively large. For both (5-1) and (5-2), when the lower limit is exceeded, the curvature of the spherical aberration becomes large, making it impossible to obtain a predetermined aperture. If the upper limit of (5-1) is exceeded,
The ratio of the small rear lens system set in (2) to the total thickness becomes large, causing the imbalance in the positive effects described above in (4). When the upper limit of (5-2)) is exceeded, the occurrence of negative distortion becomes large. Condition (6) is intended to give a large refractive index to lens L ₈ , which has a large positive effect under conditions (4) and (5), and to suppress the occurrence of convergent higher-order aberrations in L ₈ . , below the limit, the purpose cannot be achieved with only one positive lens under the above conditions. Next, an embodiment of the zoom lens system of the present invention will be shown. Example 1

【table】

【table】 Example 2

【table】 Example 3

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【table】 [Brief explanation of drawings]

Figure 1 is a lens configuration diagram of the first embodiment, Figure 2 is a lens configuration diagram of the second and third embodiments, and Figures 3 to 5 are aberration curve diagrams of the first to third embodiments, respectively. be.

Claims (1)

[Claims] 1. Consisting of a front lens component having a negative focal length from the object side and a rear lens component having a positive focal length, the front lens component and the rear lens component each extend in the optical axis direction. In a zoom lens system that fixes the focal position at a fixed position in the image field while changing the focal length of the entire lens system by moving, the front lens component is sequentially moved from the object side to the positive lens L ₁ and then to the image side. Negative lenses L ₂ , L ₃ with strong concave surfaces,
It consists of four single lenses, a positive meniscus lens L ₄ with a convex surface facing the object side, and the rear lens component consists of a biconvex positive lens L ₅ sequentially from the object side, and a positive meniscus lens L ₆ with a strong convex surface facing the object side. , consisting of four single lenses: a biconcave negative lens L ₇ and a positive lens L ₈ .
It consists of a total of eight single lenses at the front and rear, and the combined focal length of the entire zoom system on the short focal length side is f _W , the focal length of the front negative lens component is f _Fc , the focal length of the rear positive lens component is f _Rc , and the front lens component The sum of the lens thickness and air distance of the rear lens component is Σd _Fc , and the sum of the lens thickness and air distance of the rear lens component is Σd _Rc for each lens sequentially from the object side L ₁ ~
Each individual focal length of L ₈ is f ₁ - _{f 8} , the combined focal length of lens L ₅ L ₆ is f _5,6 , the sum of the lens thickness and air distance of lenses L ₅ - _{L 7} is d _{9 - 12} , lens The thickness of L ₈ is d ₁₅ ,
Similarly, when the refractive index at the d-line of the glass material with L ₈ is n ₈ , 1.6<|f _Fc /f _W |<1.8 (1) 0.34<|Σd _Fc /f _Fc |<0.41 (2-1) 1.05 <Σd _Rc /Σd _Fc <1.30 (2-2) 1.8<f ₁ /f ₄ <2.1 (3) 0.75<f _5.6 /f ₈ <0.95 (4) 0.32<d _9~12 /f _Rc <0.41 (5 -1) A wide-angle zoom lens system characterized by satisfying the following conditions: 0.14<d ₁₅ /f _Rc <0.21 (5-2) 1.7<n ₈ (6).