JPS6248809B2 - - 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 lens ratio of about 3 times. In recent years, there has been an increasing demand for a compact, high-performance zoom lens with a high zoom ratio for use in, for example, still cameras. In line with this, there has been a search for a new type of 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. One of the several types of high-power zoom lenses that have been proposed in the past is a zoom lens that consists of three lens components with positive, negative, and positive refractive power arrangements, and the lens frame structure is comparable. This is simple, but in order to increase the zoom ratio while keeping the lens compact, the refractive power of each lens component had to be strengthened, 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 by increasing or decreasing the distance between them, a variable power effect was produced, and the variable power ratio of the zoom lens was successfully increased. As a result, a compact, high-performance zoom lens with a four-group configuration with an unprecedented positive, negative, positive, and positive refractive power arrangement has been realized. 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. Consisting of four lens components, the partial system consisting of the first lens component and the second lens component has a negative composite focal length in the entire zoom range, and when zooming from the wide-angle end to the telephoto end, the first lens component and the second lens component The four lens components move toward the object side, the second lens component moves toward the image side, and the distance between the second and third lens components and the distance between the third and fourth lens components decrease. , during this time, the third lens component is fixed or slightly moved. f: focal length of the entire system at any zooming position f _w : f at wide-angle end f f _T : f f _i at telephoto end: f of i-th lens component. Focal length X _i(f) : Amount of movement of the i-th lens component when the focal length is f with the wide-angle end as a reference k _i(f) where movement toward the object side is positive and movement toward the image side is negative : Coefficient representing the ratio of the amount of movement of the i-th lens component X _{i (f)} to the amount of movement X _{1 (f)} of the first lens component at the focal length f k _{i (f)} = X _{i (f)} /X _{1(f) t1.2T :} Distance between the first and second lens components at the telephoto end _t2.3W : Distance between the second and third lens components at _the wide-angle _{end t3.4W :} Distance between _the third lens component and the fourth lens component at the wide-angle end 0.6f _w <t _1.2T <1.5f _w (1) 0.6f _w <t _2.3w <1.5f _w (2) 0.15f _w ＜t ₃ . _4w ＜0.5f _w (3) 0.5f _w ＜｜f ₂ ｜＜1.2f _w f ₂ ＜0 (4) 0.4＜k _4(f) ＜3 Each condition of (5) It is configured as a satisfying compact zoom lens. FIG. 1 shows a model layout diagram and a movement locus diagram of this zoom lens. 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 lens component and the second lens component is small, the composite focal length of this partial system is negative, and the composite focal length of the third and fourth lens components is positive, and both positive and negative The subsystems are spaced widely apart. On the other hand, on the telephoto side, the distance between the first lens component and the second lens component becomes wider, and the distance between the second lens component and the third lens component needs to be smaller. Each of the above conditions specifically defines this. 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, making it difficult to correct aberrations, mainly coma. On the other hand, if the upper limit is exceeded, large pincushion distortion will occur at the telephoto end, and spherical aberration will also be undercorrected. Condition (2) is a condition for the partial system of the second lens component and the third lens component to have a large zoom ratio, and the lower limit is a necessary limit for this purpose. If the upper limit is exceeded, the lens system will become larger, which goes against the objective of compactness, and large barrel-shaped distortion will occur on the wide-angle side, and spherical aberration will also be overcorrected. Condition (3) is a condition for increasing the contribution of the fourth lens component to zooming, and if the lower limit is exceeded, this objective will not be achieved. If the upper limit is exceeded, the zoom lens system will become larger. Condition (4) is for suppressing coma aberration occurring in the second lens component while maintaining a high zoom ratio. The upper limit is a limit that arises because it is necessary to increase the power of the second lens component in order to make the zoom lens system compact while maintaining the variable power ratio. When the lower limit is exceeded, the negative power of the second lens component becomes too strong, and accordingly, the radius of curvature of each lens surface becomes small, resulting in significant coma aberration.
Furthermore, the curvature of field is also overcorrected. Condition (5) relates to the relative movement of the third lens component with respect to the first lens component, and exceeding the lower limit means that the movement of the fourth lens component becomes smaller, and its contribution to the zoom ratio becomes smaller. Conversely, if the upper limit is exceeded, the contribution to the zoom ratio increases, but the distance from the second lens component becomes too wide on the wide-angle side, resulting in insufficient correction of spherical aberration. A zoom lens that satisfies the above conditions is desirably configured to further satisfy the following conditions. The first lens component consists of a cemented lens consisting of a positive and negative single lens and a positive single lens, the second lens component consists of two negative lens groups and one positive lens group, and the third lens component is composed of at least one positive lens and at least one negative lens group, the fourth lens component is composed of at least two positive lens groups, and NN _i : average refraction of the negative lens of the i-th lens component Rate νP _i : Average Atsube number of the positive lens of the i-th lens component νN _i : Average Atsube number of the negative lens of the i-th lens component 0.5f _T <f ₁ <1.5f _T (8) 1.7<NN ₂ ( 9) 40＜νP ₁ (10) 40＜νN ₂ (11) If the focal length of the first lens component exceeds the lower limit in condition (8), the spherical aberration at the telephoto side will be insufficiently corrected, and furthermore, the spherical aberration at the telephoto side will be Pincushion distortion becomes large. Conversely, if the upper limit is exceeded, spherical aberration will be overcorrected on the wide-angle side, and barrel-shaped distortion will further increase on the wide-angle side. Condition (9) is a condition for keeping the Petzval sum appropriate. If this refractive index exceeds the lower limit, the radius of curvature of the negative lens will have to become smaller, and the Petzval sum will become too small and the curvature of the sagittal field will become large. Moreover, the occurrence of coma flare increases. Conditions (10) and (11) relate to chromatic aberration correction, and condition (10) is a condition for satisfactorily correcting the color of the first lens component, which is a necessary condition for correcting chromatic aberration of the entire zoom lens system. Furthermore, the quality of the color correction of the second lens component, which has the strongest refractive power among the lens components, is largely influenced by all lenses, and the condition (11) is for this purpose. Examples of the zoom lens system of the present invention will be shown below. In this embodiment, the third lens component is fixed and the first and fourth lens components move as a unit.

【table】

[Table] FIG. 3 shows aberration diagrams of these examples. It goes without saying that in these embodiments, if the lens components that are fixed or moved together with other lens components are moved independently, the degree of freedom of the system increases and it is more advantageous for aberration correction.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the structure of a zoom lens according to the present invention and a diagram of movement loci of each lens component, and FIGS. 2 and 3 are a cross-sectional view of the lens and an aberration diagram of an embodiment, respectively.

Claims (1)

[Claims] 1. In order from the object side, a first lens component including at least a positive single lens and a negative single lens and having a positive focal length, at least two negative lens groups, and a negative a second lens component having a focal length of at least one positive lens group and at least one negative lens group; and a third lens component having a positive focal length, also consisting of at least two positive lens groups. a fourth lens configured and having a positive focal length.
The partial system consisting of the first lens component and the second lens component has a negative composite focal length in the entire zoom range, and when zooming from the wide-angle end to the telephoto end, the first lens component, the fourth lens component The lens component moves to the object side, the second lens component moves to the image side, and the distance between the second and third lens components and the distance between the third and fourth lens components decrease, and during this time The third lens component is fixed or slightly moved. f: Focal length of the entire system at any zooming position f _W : f at the wide-angle end f _T : f at the telephoto end fi: Focal length of the i-th lens component Xi _{(f )} : Amount of movement of the i-th lens component when focal length f is based on the wide-angle end (movement toward the object side is positive, movement toward the image side is negative) ki _(f) : At focal length f The amount of movement of the i-th lens component of
Coefficient representing the ratio of Xi _(f) to the amount of movement of the first lens component X _1(f) ki _(f) = Xi _(f) /X _1(f) t ₁ , _2T : First lens component at the telephoto end and the second lens component t ₂ , _3W : The distance between the second lens component and the third lens component at the wide-angle end t ₃ , _4W : The distance between the third lens component and the fourth lens component at the wide-angle end NNi: Average refractive index of the negative lens of the i-th lens component νPi: Average Atsube number of the positive lens of the i-th lens component νNi: Average Atsube number of the negative lens of the i-th lens component 0.6f _W <t ₁ , _2T ＜1.5f _W 0.6f _W ＜t ₂ , _3W ＜0.5f _W 0.15f _W ＜t ₃ , _4W ＜0.5f _W 0.5f _W ＜｜f ₂ ｜＜1.2f _W f ₂ ＜0 0.4＜k _{4(f )} <3 0.5f _T <f ₁ <1.5f _T 1.7<NN ₂ 40<νP ₁ 40<νN ₂ A compact zoom lens that satisfies the following conditions.