JPH0360411B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a zoom lens for a single-lens reflex camera having an F number of about 4 and a zoom ratio of about 3 times from wide angle to medium telephoto. Regarding zoom lenses with the above specs, so-called two-group type zoom lenses have been known that change the magnification by changing the mutual spacing between a front group with negative refractive power and a rear group with positive refractive power. There is. However, when trying to achieve a two-group type with a zoom ratio of about 3x as described above, the amount of movement due to zooming of the rear group becomes too large, and the aperture that moves along with the rear group becomes too large. On the other hand, in order to maintain the precision of the automatic aperture mechanism at a high level, a complicated mechanism is required, resulting in drawbacks such as an increase in the size of the mechanical system, or when attempting to reduce the amount of movement of the rear group. The total length of the lens increases on the focal side, leading to an increase in the lens diameter in order to secure the necessary amount of peripheral light, or it becomes necessary to strengthen the refractive power of each lens group to reduce the total lens length, which reduces various aberrations. There are drawbacks such as an increase in the number of lenses or the need to increase the number of lenses in order to correct aberrations. The present invention has focused on this point, and aims to provide a high-power zoom lens with excellent performance, in which the amount of movement of each lens group including the lens group with an aperture is small, and the overall length is short. First, to describe the configuration of the present invention, in order from the object side, there are a first lens that is a positive lens, a second lens that is a negative meniscus lens with a convex surface facing the object side, a third lens that is a negative lens, and the third lens. and a fourth lens which is a positive lens laminated together and has negative refractive power as a whole; a fifth lens which is a positive lens, a sixth lens which is a positive lens, and the sixth lens; a seventh lens group consisting of a negative lens laminated together and having a positive refractive power as a whole; an eighth lens group consisting of a positive lens;
a 9th lens that is a negative lens and a 10th lens that is a negative lens that are laminated together with the lens, and has a negative refractive power as a whole; an 11th lens that is a positive lens; and the 11th lens that is a positive lens; It consists of a 12th lens, which is a negative lens, and a 13th lens, which is a positive lens, and has a positive refractive power as a whole, and all four groups are movable. Therefore, it is an optical system that performs magnification change, and is a zoom lens characterized by satisfying the following conditions. (1) 1.1＜｜f〓｜／fw＜1.7, f〓＜0 (2) 0.8＜f〓／fw＜1.2 (3) 1.1＜｜f〓｜／fw＜1.7, f〓＜0 (4) 1.8＜f〓／fw＜2.4 (5) 8＜f ₁ /fw＜50 (6) n ₄ −n ₃ ＞0.2 (7) n ₈ −n ₉ ＞0.15 (8) n ₁₂ −n ₁₁ ＞0.2 ( 9) 0.45<｜r ₁₉ |/fw<0.6, r ₁₉ <0 f〓: Composite focal length of the 1st lens group f〓: Composite focal length of the 1st lens group f〓: Composite focal length of the 1st lens group f〓: Synthetic focal length fw of the 1st lens group: Shortest focal length of the entire system f ₁ : Focal length n _i of the 1st lens: Refractive index of the glass material used for the i-th lens r ₁₉ : Bonded surface of the 11th lens and 12th lens In the present invention configured in this way, the so-called polarity radius of 2
The basic group type is that the rear group is further divided into three lens groups from the object side, that is, four lens groups in total, and the magnification is changed by changing all the spacing between the four lens groups. . This configuration increases the degree of freedom in the movement of each lens group during zooming, increases the merits in aberration correction, and allows the movement of each lens group, including the groups associated with the diaphragm, to be controlled to a small amount. becomes possible. Next, each of the above conditions will be explained. Condition (1) relates to the refractive power of the first lens group. conditions
If the lower limit of (1) is exceeded, the refractive power of the first lens group becomes too strong, causing overcorrected spherical aberration and astigmatism, making it difficult to maintain good optical performance. Furthermore, if the upper limit of condition (1) is exceeded, the refractive power of the first lens group will weaken, and it may not be possible to secure the back focus necessary for a single-lens reflex camera lens.
Alternatively, there is a drawback that the overall length of the lens becomes long in order to secure back focus. Conditions (2), (3), and (4) are related to the refractive power of the first, second, and third lens groups, respectively, and together they minimize the number of lens components and minimize the amount of movement of each lens group. This is a necessary condition to suppress it. When the lower limits of conditions (2), (3), and (4) are exceeded, the refractive powers of the first, third, and third lens groups become too strong,
This is undesirable because various aberrations are increased or the lens structure becomes complicated to correct the aberrations. Also, conditions (2), (3),
If the upper limits of (4) are exceeded, the refractive powers of the first, second, and third lens groups will become too weak and the amount of movement will become too large, causing the above-mentioned problems or increasing the overall length. produce defects. In the case of the present invention, by satisfying conditions (2), (3), and (4), the lens configuration of the first, second, and third lens groups can be configured with the minimum number of lenses, which is three lenses each. It became possible. Condition (5) relates to the refractive power of the first lens group. 1st
The lens has a weak refractive power and plays an effective role in correcting distortion, especially on the short focal length side. When the lower limit of condition (5) is exceeded, the refractive power of the first lens group becomes strong and the effect of correcting distortion becomes strong, but on the other hand, chromatic aberration of magnification occurs for the beam of light that should be focused on the periphery of the screen. Undesirable. If the upper limit of condition (5) is exceeded, the refractive power of the first lens group becomes too weak, the effect of the first lens is weakened, and distortion cannot be corrected. Condition (6) relates to the refractive index of the glass materials used for the third and fourth lenses. The third lens and the fourth lens are laminated together in the lens group, and the effect of the laminated surface mainly contributes to correction of spherical aberration and chromatic aberration. If condition (6) is violated, the convergence effect on the bonded surfaces will be weakened, and overcorrected spherical aberration will remain in the entire first lens group. In addition, in order to maintain good chromatic aberration, condition (6) must be satisfied, and when the Atsube numbers of the glass materials used for the third and fourth lenses are ν ₃ and ν ₄ , respectively, ν ₃ - _{ν 4} It is desirable to satisfy >20. Condition (7) relates to the refractive index of the glass materials used for the eighth and ninth lenses. The eighth lens and the ninth lens are laminated and used in the lens group, and the effect of the laminated surface mainly contributes to correction of spherical aberration and axial aberration. If condition (7) is violated,
The convergence effect on the bonded surfaces is weakened, and overcorrected spherical aberration and axial chromatic aberration remain. In order to highly correct axial chromatic aberration, condition (7) must be satisfied, and when the Atsube numbers of the glass materials used for the 8th and 9th lenses are ν ₈ and ν ₉ , respectively, ν ₉ −ν ₈
It is desirable to satisfy >20. Condition (8) relates to the refractive index of the glass material used for the 11th lens and the 12th lens. The 11th lens and the 12th lens are used in a bonded state within the lens group, and the effect of the bonded surface mainly contributes to correction of spherical aberration and lateral chromatic aberration. If condition (8) is violated, the divergence effect on the bonded surfaces will be weakened, and undercorrected spherical aberration and chromatic aberration of magnification will remain, which is undesirable. In addition, in order to correct lateral chromatic aberration to a higher degree, condition (8) must be satisfied, and when the Atsube numbers of the glass materials used for the 11th lens and the 12th lens are ν ₁₁ and ν ₁₂ , respectively, ν ₁₂ It is desirable to satisfy −ν ₁₁ >10. Condition (9) relates to the radius of curvature of the bonding surface of the 11th lens and the 12th lens. This condition (9), together with condition (8), contributes to the correction of spherical aberration, chromatic aberration, and distortion aberration. If the lower limit of condition (9) is exceeded, the radius of curvature of the bonded surface becomes small, the divergence effect increases too much, and overcorrected spherical aberration occurs, which is not preferable.
On the other hand, when the upper limit of condition (9) is exceeded, the radius of curvature of the bonded surface increases, the divergence effect weakens, chromatic aberrations, especially lateral chromatic aberrations, remain large, and the effect of correcting distortion aberrations weakens, especially for short focal lengths. Barrel-shaped distortion remains on the distance side, which is undesirable. Examples of the present invention will be described below. Here, r is the radius of curvature of each lens surface, d is the lens thickness or distance between lenses, n is the refractive index of each lens, and ν is the Abbe number of each lens.

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【table】 [Brief explanation of drawings]

Figure 1 is a lens diagram of Example 1, Figures 2 and 3 are aberration diagrams of Example 1 at the short focus side and long focus side, respectively, Figure 4 is a lens diagram of Example 2, and Figure 5. , 6th
The figures are aberration diagrams of Example 2 on the short focus side and long focus side, FIG. 7 is a lens diagram of Example 3, and FIGS. 8 and 9 are aberration diagrams of Example 3 on the short focus side and long focus side, respectively. It is an aberration diagram at .

Claims (1)

[Claims] 1. In order from the object side, a first lens that is a positive lens;
The second negative meniscus lens with the convex surface facing the object side.
a fifth lens group that is composed of a lens, a third lens that is a negative lens, and a fourth lens that is a positive lens bonded to the third lens and has negative refractive power as a whole; a fifth lens that is a positive lens; a sixth lens that is a positive lens; and a seventh lens that is a negative lens bonded to the sixth lens, and has a positive refractive power as a whole; an eighth lens that is a positive lens; a ninth lens, which is a negative lens laminated with the eighth lens, and a tenth lens, which is a negative lens, and has a negative refractive power as a whole; an eleventh lens, which is a positive lens; , a twelfth lens which is a negative lens laminated with the eleventh lens;
An optical system consisting of a 13th lens, which is a positive lens, and a 3rd lens group having positive refractive power as a whole, and which performs magnification change by moving all of the four groups, and includes the following: A zoom lens that satisfies the following conditions. (1) 1.1＜｜f〓｜／fw＜1.7, f〓＜0 (2) 0.8＜f〓／fw＜1.2 (3) 1.1＜｜f〓｜／fw＜1.7, f〓＜0 (4) 1.8＜f〓／fw＜2.4 (5) 8＜f ₁ /fw＜50 (6) n ₄ −n ₃ ＞0.2 (7) n ₈ −n ₉ ＞0.15 (8) n ₁₂ −n ₁₁ ＞0.2 ( 9) 0.45<｜r ₁₉ |/fw<0.6, r ₁₉ <0 f〓: Composite focal length of the 1st lens group f〓: Composite focal length of the 1st lens group f〓: Composite focal length of the 1st lens group f〓: Synthetic focal length fw of the 1st lens group: Shortest focal length of the entire system f ₁ : Focal length n _i of the 1st lens: Refractive index of the glass material used for the i-th lens r ₁₉ : Bonded surface of the 11th lens and 12th lens radius of curvature.