JPS6151297B2 - - Google Patents

Description

[Detailed description of the invention]

This invention is a zoom lens used for still cameras, etc., which ranges from wide-angle to semi-telephoto.
The present invention relates to a compact zoom lens with a zoom ratio of approximately 3 times. In recent years, there has been an increasing demand for compact, high-performance zoom lenses with high zoom ratios, such as those used in steel caneras. In line with this trend, a search has been made for a new time zoom lens that overcomes the limitations of so-called mechanical correction type and optical correction type zoom lenses that have been developed in the past. Positive, negative,
There are zoom lenses that are composed of three lens components with a positive refractive power arrangement, and the lens frame structure is relatively simple. had to be made stronger, which created difficulties in correcting aberrations. In this invention, the positive third lens component of the zoom lens consisting of the above-mentioned positive, negative, and positive three lens components is
By dividing the lens into two positive lens components, the refractive power of each lens component was reduced, and the interval between the positive lens components was used for aberration correction. That is, the fourth lens component moves relative to the third lens component, and contributes to aberration correction in the same sense as a floating mechanism normally used in wide-angle lenses and macro lenses. Especially wide-angle,
This relative movement is effective against image curvature, which tends to be under-corrected at both telephoto ends and over-corrected at the middle. Decreased,
It is desirable to change so that it increases again. Furthermore, a positive lens component with weak refractive power is placed between the divided lens components and the image to correct distortion at the telephoto end. This result is correct,
This is a compact, high-performance zoom lens with a 5-group configuration with an unprecedented power distribution of negative, positive, positive, and positive. Specifically, from the object side, the first lens component has a positive focal length, the second lens component has a negative focal length, the third lens component has a positive focal length, and the third lens component also has a positive focal length. 4 lens components, and a 5th lens component having a weak positive refractive power that always maintains a constant position with respect to the image plane or moves slightly with respect to the image plane between the 4th lens component and the image plane, and the 1st lens component The subsystem consisting of the and second lens component has a negative composite focal length, and when zooming from the wide-angle end to the telephoto end, the first lens component, the third lens component, and the fourth lens component move toward the object side. , the distance between the first lens component and the second lens component increases, and the distance between the first lens component and the second lens component increases;
The distance between the lens component and the third lens decreases, and the distance between the lens component and the third lens decreases.
The lens components are moved or fixed. f: Focal length of the entire system at any zooming position f _W : Focal length of the entire system at the wide-angle end f _T : Focal length of the entire system at the telephoto end f _i : i-th lens Focal length of component X _i (f): Based on the wide-angle end position, the amount of movement of the i-th lens component when the focal length is f, with movement toward the object side being positive and movement toward the image side being negative. k _i (f): a coefficient representing the ratio between the amount of movement X _i (f) of the i-th lens component and the amount of movement X(f) of the first lens component at the focal length f. k _i (f) = X _i (f) / X ₁ (f) t ₁ . _2T : Distance between the first lens component and the second lens component at the telephoto end t ₂ . _3W : Second lens at the wide-angle end When the distance between the component and the third lens component is 0.4f _W <t _1.2T < _{1.2f W} (1) 0.4f _W <t _2.3W < _{1.2f W} (2) −0.3f _W <X _{2( fT)} ＜0.3f _W (3) −0.5f _W ＜X _5(fT) ＜0.5f _W (4) 0.3＜k ₃ (f)＜1.5 (5) 0.3＜k ₄ (f)＜1.5 (6) It is configured as a compact zoom lens with a zoom ratio of approximately 3 times, satisfying the following conditions: 0.4f _W <|f ₂ | <1.5f _W (7) 0.5f _T <f ₅ <4f _T (8). A model layout of this zoom lens is shown in FIG. In order to correct aberrations, it is desirable to have a retrofocus type lens arrangement on the wide-angle side and, conversely, a telephoto type lens arrangement on the telephoto side. Therefore, on the wide-angle side, the distance between the first and second lens components is small, the composite focal length of this partial system is negative, and the third
The composite focal length of the partial system consisting of the lens component and the fourth lens component is positive, and the interval between the positive and negative partial systems is wide. On the other hand, on the telephoto side,
The distance between the first lens component and the second lens component must be increased, and the distance between the second lens component and the positive subsystems below the third lens component must be decreased. The conditions (1) to (7) above specifically stipulate this. That is, condition (1) is a condition for increasing the contribution of the partial system consisting of the first lens component and the second lens component to the zoom ratio. In order to exceed the lower limit and still achieve a high zoom ratio, it is necessary to increase the powers of the first and second lens components, and the occurrence of aberrations, mainly coma, becomes significant. On the other hand, if the upper limit is exceeded, large pincushion distortion will occur at the telephoto end.
Spherical aberration is also undercorrected. Condition (2) relates to the arrangement of the second lens component and the third and fourth lens components.The lower limit is the limit to prevent the contribution to the zoom ratio from becoming smaller, and if the upper limit is exceeded, the lens system becomes larger and it becomes difficult to make it compact. This limit was established to defeat the purpose, but at the same time, large barrel-shaped distortion aberration occurs on the wide-angle side, creating difficulties in correcting the aberration. Condition (3) relates to the movement of the second lens component; if the upper limit is exceeded, the amount of movement of the first lens component will have to increase in order to increase its contribution to the zoom ratio, resulting in a large pincushion at the telephoto end. This results in mold distortion. If the lower limit is exceeded, t _{1 .2T} in condition (1) becomes large, causing the above-mentioned difficulty. Condition (4) relates to movement of the fifth lens component. Fifth
The role of the lens component is to correct pincushion distortion that occurs at the telephoto end, and its movement is limited to suit this purpose. The upper limit is the limit for this,
The lower limit is provided to prevent the outer diameter of the fifth lens component from becoming too large and to suppress the occurrence of coma aberration. Conditions (5) and (6) are related to the relative movement of the third and fourth lens components with respect to the first lens component, and the fact that both conditions exceed the lower limit means that the second lens component and the rear positive As the distance from the lens component increases, its contribution to the zoom ratio becomes smaller, and higher-order spherical aberrations tend to be undercorrected on the telephoto side. On the other hand, when the upper limit is exceeded, the contribution to the zoom ratio increases, but the distance between the second lens component and the positive lens component becomes too wide on the wide-angle side, resulting in insufficient correction of spherical aberration on the wide-angle side. Conditions (7) and (8) are related to the focal length of each lens component, and condition (7) indicates the minimum refractive power necessary to make a compact, high-power zoom lens. This goal cannot be achieved. Furthermore, if the lower limit is exceeded, significant coma flare will occur and field curvature will be insufficiently corrected. Condition (8), similar to condition (4), is for correcting pincushion distortion on the telephoto side using the fifth lens component.
The upper limit is set to achieve this purpose; if the lower limit is exceeded, coma flare will occur significantly. It is desirable that the zoom lens of the present invention having the above-mentioned basic configuration further satisfies the following conditions when put into practice. The first lens component is composed of a cemented lens of positive and negative single lenses and a positive single lens, the second lens component is composed of two negative lens groups and one positive lens group, and the third lens component is composed of two negative lens groups and one positive lens group. is composed of at least one positive lens group and at least one negative lens group,
The fourth lens component is composed of at least two positive lens groups, and the fifth lens group includes at least one positive lens group. NN _i : Average value of the refractive index of the negative lens of the i-th lens component νP _i : Average value of the Atbe number of the positive lens of the i-th lens component νN _i : Average value of the Abbe number of the negative lens of the i-th lens component r _A : Average value of the Abbe number of the negative lens of the i-th lens component When the radius of curvature is 0.3f _W <r _A <0.9f (9) 1.7<NN ₂ (10) 40<νP ₁ (11) 40<νN ₂ (12) In a zoom lens configured as in this invention, How the second lens component is configured is important for correcting aberrations, and conditions (9) and (10) relate to this. Condition (9) is an important condition regarding the correction of coma aberration; if r _A exceeds the lower limit, coma flare will occur significantly, and conversely, if r A exceeds the upper limit, it will cause insufficient correction of field curvature on the wide-angle side. Condition (10) is a condition for maintaining an appropriate Petzval sum; if this refractive index is too small, the radius of curvature will inevitably become small, and coma flare will occur. Conditions (11) and (12) relate to chromatic aberration correction, and it is natural that even in high-power zoom lenses, it is desirable for each lens component to be achromatized as much as possible, but especially for the first lens component. needs to be well corrected. This is condition (11). Furthermore, since the second lens component having a large refractive power has a large influence on the correction of chromatic aberration, it is desirable that condition (12) be satisfied. Examples will be described below, but Examples 1 to 3 are examples in which the second lens component and the fifth lens component are fixed, and the first lens component and the third lens component are moved as one body.
Similarly, in Example 4, the second lens component and the fifth lens component are fixed, and the first lens component and the fourth lens component are fixed.
This is an example of moving as a body. Although this movement method, which is disadvantageous for aberration correction, is adopted in order to simplify the lens frame structure, sufficient aberration correction is achieved as shown in FIGS. 6 to 9.

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】 [Brief explanation of the drawing]

Fig. 1 shows the basic lens configuration of the zoom lens of the present invention and its movement trajectory, Figs. 2 to 5 show lens cross sections and movement trajectory of Examples 1 to 4, respectively, and Figs. 6 to 9 are aberration diagrams of Examples 1 to 4, respectively.

Claims (1)

[Claims] 1. In order from the object side, a first lens component having a positive focal length, a second lens component having a negative focal length, a third lens component having a positive focal length, and a lens component also having a positive focal length. a fourth lens component with a weak positive refractive power, and a fifth lens component with a weak positive refractive power provided between the fourth lens component and the image plane; When zooming from the wide-angle end to the telephoto end, the first lens component and the third and fourth lens components move toward the object side, and the distance between the first lens component and the second lens component increases. Then, the distance between the fourth lens component and the fifth lens component increases, and the distance between the second lens component and the third lens component decreases, and during this period, the second lens component and the fifth lens component are fixed or slightly moved. , f: Focal length of the entire system at any zooming position f _W : Focal length of the entire system at the wide-angle end f _T : Focal length of the entire system at the telephoto end f _i : Focal length of the i-th component X _i ( f): Using the wide-angle end position as a reference, the amount of movement of the i-th lens component when the focal length is f, with movement toward the object side being positive and movement toward the image side being negative. k _i (f): Coefficient representing the ratio between the amount of movement of the i-th lens component X _i (f) and the amount of movement of the first lens component X ₁ (f) at focal length f k _i (f)=X _{i ( f ) / _} When the interval is 0.4f _W <t _1.2T < _{1.2f W} 0.4f _W <t _2.3W < _{1.2f W} −0.3f _W <X ₂ (f _T )<0.3f _W −0.5f _W <X ₅ (f _T )<0.5f _W 0.3<k ₃ (f)<1.5 0.3<k ₄ (f)<1.5 0.4f _W <|f ₂ |<1.5f _W 0.5f _T <f ₅ <4f _T conditions A compact zoom lens that satisfies your needs.