JPH0256644B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention has a zoom ratio of 3 from a wide angle range of 76 degrees on the short focus side for 35 mm single-lens reflex cameras.
This invention relates to a zoom lens that is very compact, has a short overall length of the lens system, and has good aberrations. A zoom lens with high utility value is desired for compact normal photography that includes a wide-angle range, has a high magnification ratio, and is compact. Conventionally, a two-group zoom lens has been typical as a zoom lens that is preceded by a lens group having a negative composite refractive power. However, although this two-group zoom lens is simple to construct, if you try to construct a zoom lens system with a high zoom ratio of 2x or more, the fluctuations in various aberrations will be large and correction will be difficult. It has been difficult to obtain a compact zoom lens with good aberrations due to the large amount of movement of the group. The present invention has a configuration in which the positive lens group at the rear of the two-group zoom lens is divided into a positive second lens group, a negative third lens group, and a positive fourth lens group. It has a telephoto type configuration, with the first lens group and second lens group, and the third and fourth lens groups close to each other on the long focal length side, and the combined refractive power consists of two groups, one positive and one negative. I'm taking it. In order to achieve a more compact design than in the past, it is necessary to shorten the focal lengths of the second and third lens groups, which increases various aberrations and makes correction very difficult. The present invention aims to reduce aberration fluctuations and movement amounts of each group due to zooming, thereby enabling a compact configuration with good aberrations. In the present invention, as illustrated in FIGS. 1 and 2, in order from the object side, the first lens group 1 or 1' having a negative composite refractive power has a negative meniscus G with a strong concave surface facing the image side. ₁ , a positive meniscus G ₂ with a strongly convex surface facing the image side, or a positive lens G′ ₁ with a strongly convex surface facing the object side, a negative meniscus G′ 2 with a strongly concave surface facing the image side, and a strong lens G′ ₂ with a strong convex surface facing the image side. Negative lens with concave side facing
G ₃ , a positive meniscus with a strongly convex surface facing the object side.
The second lens group 2 is made up of a negative meniscus lens G ₄ with a strong concave surface facing the image side and a positive lens G ₆ with _a strong convex surface facing the object side. The third lens group has a positive composite refractive power, consisting of a positive lens G ₇ with a strong convex surface facing the object side and a negative meniscus G ₈ lens with a strong concave surface facing the object side. 3 or 3' is a composite negative lens made by cementing a positive lens G ₉ with a strongly convex surface facing the image side and a negative lens G ₁₀ with a strongly concave surface facing the object side, and a negative lens with a strongly concave surface facing the object side. The fourth lens group 4 is composed of a single or cemented negative lens G ₁₁ or G′ ₁₁ and has a positive composite refractive power.
Consisting of a positive lens G ₁₂ with a strongly convex surface facing the image side, a positive lens G ₁₃ with a strongly convex surface facing the image side, and a negative meniscus G ₁₄ with a strongly concave surface facing the object side, it is the first lens on the short focus side. The air distance between the lens group 1 or 1' and the second lens group 2 and the third lens group 3 or 3' and the fourth lens group
The air gap between lens groups 4 decreases on the long focal point side,
The first, second, third, and fourth lens groups 1 or 1 are arranged so that the air distance between the second lens group 2 and the third lens group 3 or 3' on the short focus side increases on the long focus side. An optical system that performs magnification by moving the respective groups ', 2, 3, 3', and 4 in relation to each other, and performs focusing by moving the first lens group 1 or 1' alone, which satisfies the following conditions. This is a compact, wide-angle, high-variable zoom lens. (1) 0.85<f ₂ /fw<0.95 (2) 0.8<R ₁₂ /f ₂ <1.2 (3) 1.63<N ₆ , N ₇ <1.7 (4) 50<ν ₆ , ν ₇ (5) D ₂ +D ₃ = constant where fw...the shortest focal length of the entire zoom lens system fi...the focal length of the th lens group Ri...the radius of curvature of the th lens surface Ni...the d-line refractive index of the th glass material νi...the th The Atsube number of the d-line of the glass material Di...The distance between the principal points of the 1st lens group and the (i+1)th lens group Next, to explain the features of the present invention in detail, in order to obtain a compact zoom lens system, the second lens of the present invention The focal length of group 2 was set shorter than the shortest focal length of the zoom lens system. Condition (1) is such that if the upper limit of the focal length range of the second lens group 2 for obtaining a compact zoom lens is exceeded, the objective condition for obtaining a compact structure is deviated from. If the lower limit is exceeded, it becomes extremely difficult to correct spherical aberration, especially on the long focal length side. In the case of FIG _. 1 in which the first lens group of the present invention has a configuration in which the negative lens precedes the negative lens G ₁ and the positive lens G ₂ , the effective diameter is smaller than that in FIG. It is small and good, F3.5 on the wide-angle side with a field of view of 76°.
Although it is a large diameter for its class, the filter diameter is φ55mm.
That's fine. However, in this configuration, the spherical aberration changes toward the over side on the long focal point side due to zooming, making correction difficult. In order to correct this, the second lens group 2
A positive lens with a strongly convex surface facing the object side is installed, but condition (2) is the appropriate range of this convex surface; if the upper limit is exceeded, coma aberration worsens on the long focal point side and flare occurs. If the lower limit is exceeded, the spherical aberration becomes even more excessive on the long focal point side, and the curvature of field becomes considerably less, making it impossible to correct these aberrations with other lens surfaces. Furthermore, when using the positive lens preceding type as shown in FIG. 2, fluctuations in spherical aberration due to zooming can be further reduced. Although the effective diameter of the front lens is larger than that of the negative lens advanced type shown in FIG. 1, it is not within a range that would be contrary to compactness. In the case of a negative, positive, negative, and positive four-group configuration, the light ray that passes through the corner on the long focal point side and the maximum ray that is parallel to the optical axis pass through almost the same place in the second lens group 2. In such a case, it is very difficult to correct longitudinal chromatic aberration and lateral chromatic aberration on the long focal point side. Second lens group 2 of the present invention
is composed of two cemented lenses having a positive composite refractive index, which are made by cementing a negative meniscus lens with a difference in refractive index and a difference in Abbe number, and a biconcave lens. This corrects various aberrations, especially chromatic aberration, within the entire focal length from the wide-angle side to the long focal length side.
Conditions (3) and (4) are appropriate ranges for the refractive index and Atsube number of the glass material of this biconvex lens, and if they deviate from these conditions, it is impossible to correct chromatic aberration, especially on the long focal length side, with other lens groups. It is possible. In addition to chromatic aberration, if the upper limit of condition 3 is exceeded, coma aberration on the long focal point side will worsen and flare will occur considerably. If the lower limit is exceeded, the meridional luminous flux becomes excessive on the long focal point side and the astigmatism difference becomes large, and it is difficult to correct this using anything other than the second lens group. In the present invention, as in condition (5), the second lens group 2 and the fourth lens group 4 move together during zooming, and the third lens group 3 or 3' moves independently to absorb aberration fluctuations caused by zooming. It was formed to be. It can be easily assumed that by doing this, the number of lens group drive cams can be reduced, and the lens can be assembled easily and with high precision while being compact, and costs such as parts processing and assembly adjustment man-hours can be reduced. In addition, by cementing G ₁₁ of the third lens group 3 of the present invention with a positive meniscus on the image side and replacing it with a negative lens with a strongly concave surface facing the image side as the composite lens G' ₁₁ , coma flare on the long focal length side can be reduced. can be made even smaller. Next, examples of the present invention will be shown. Example 1 f=28.7~50~82.8 FNo.3.5~4.0~4.8 _f2 =25.7
_f2 /fw=0.895 _R12 / _f2 =0.886

[Table] Example 2 f=28.7~50~82.9 FNo.3.5~4.0~4.8 _f2 =25.7
_f2 /fw=0.895 _R12 / _f2 =0.994

[Table] As can be seen from the aberration diagrams of FIGS. 3 and 4 in the examples, it is clear that the zoom lens maintains excellent imaging performance even when changing magnification by zooming.

[Brief explanation of drawings]

Figure 1 is a lens configuration diagram of Example 1 of the present invention, Figure 2 is a lens configuration diagram of Example 2, each figure in Figure 3 is of Example 1, and each figure in Figure 4 is of Example 2. FIG. 4 is a diagram showing various aberrations at each focal length for an object at infinity. Note that S in FIGS. 3 and 4 is a sagittal image plane, and M is a meridional image plane. Gi...each single lens from the object side, 1...first lens group, 2...second lens group, 3...third lens group,
4...Fourth lens group.

Claims (1)

[Claims] 1 Consists of 4 lens groups, the second lens group is
A composite positive lens is made by cementing a negative meniscus lens with a concave surface facing the image side, and a positive lens with a convex surface facing the object side, in order from the object side, and a positive lens with a convex surface facing the object side, and a positive lens with a convex surface facing the object side. It is a lens group having a positive composite refractive power consisting of a composite positive lens cemented with a negative meniscus lens facing toward the object side, and the fourth lens group is a positive lens with a convex surface facing the image side in order from the object side, a positive lens with a convex surface facing the image side, This is a lens group with positive synthetic refractive power consisting of a positive lens with a convex surface facing toward the object side and a negative meniscus lens with a concave surface facing toward the object side. It is a lens group having a negative synthetic refractive power consisting of a meniscus lens, a positive meniscus lens with a convex surface facing the image side, a negative lens with a concave surface facing the image side, and a positive meniscus lens with a convex surface facing the object side. A negative composite lens in which the lens group consists of a positive lens with a convex surface facing the image side and a negative lens with a concave surface facing the object side, in order from the object side, and a negative lens with a concave surface facing the object side. Consists of lens groups with refractive power, and the air distance between the first and second lens groups on the short focus side and the air distance between the third and fourth lens groups decreases on the long focus side. The first,
A compact optical system that performs magnification by moving the second, third, and fourth lens groups relative to each other and focusing by moving the first lens group independently, and which satisfies the following conditions: A wide-angle, high-variability zoom lens. 1 0.85<f ₂ /fw<0.95 2 0.8<R ₁₂ /f ₂ <1.2 3 1.63<N ₆ , N ₇ <1.7 4 50<ν ₆ , ν ₇ 5 D ₂ +D ₃ = constant Here fw...Zoom lens Shortest focal length of the entire system fi...Focal length of the i-th lens group Ri...Radius of curvature of the i-th lens surface Ni...Refractive index of the d-line of the i-th glass material νi...D-line of the i-th glass material Atsube number Di... Distance between principal points of the i-th lens group and the (i+1)-th lens group. 2 Consists of 4 lens groups, the second lens group is
A composite positive lens is made by cementing a negative meniscus lens with a concave surface facing the image side, and a positive lens with a convex surface facing the object side, in order from the object side, and a positive lens with a convex surface facing the object side, and a positive lens with a concave surface facing the object side. It is a lens group having a positive composite refractive power consisting of a composite positive lens cemented with a negative meniscus lens facing toward the object side, and the fourth lens group is a positive lens with a convex surface facing the image side in order from the object side, a positive lens with a convex surface facing the image side, A lens group with a positive composite refractive power consisting of a positive lens with a convex surface facing toward the object side and a negative meniscus lens with a concave surface facing the object side, and the first lens group has a convex surface facing the image side in order from the object side. Positive lens, negative meniscus lens with concave surface facing the image side,
A lens group having negative synthetic refractive power consisting of a negative lens with a concave surface facing the image side and a positive meniscus lens with a convex surface facing the object side, and the third lens group is a positive lens with a convex surface facing the image side. and a negative lens with a concave surface facing the object side, as well as a composite negative lens with a negative lens with a concave surface facing the image side and a negative lens with a convex surface facing the object side. The air gap between the first lens group and the second lens group on the short focal length side and the air gap between the third lens group and the fourth lens group decrease on the long focal length side, and , zooming is performed by moving the first, second, third, and fourth lens groups relative to each other so that the air gap between the second lens group and the third lens group on the short focal length side increases on the long focal length side. A compact wide-angle, high-variable-power zoom lens is an optical system that performs focusing by independently moving a first lens group, and is characterized in that it satisfies the following conditions. 1 0.85<f ₂ /fw<0.95 2 0.8<R ₁₂ /f ₂ <1.2 3 1.63<N ₆ , N ₇ <1.7 4 50<ν ₆ , ν ₇ 5 D ₂ +D ₃ = constant Here, fw...Zoom lens Shortest focal length of the entire system fi...Focal length of the i-th lens group Ri...Radius of curvature of the i-th lens surface Ni...Refractive index of the d-line of the i-th glass material νi...D-line of the i-th glass material Atsube number Di... Distance between principal points of the i-th lens group and the (i+1)-th lens group.