JPH0125044B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a zoom lens system, and an object of the present invention is to improve the zoom lens system. That is, the zoom lens system of the present invention has the first and fourth lenses.
As is clear from Figure 7, in order from the object side, there is a fixed front group, a variable magnification lens group that is movable for variable magnification, and the lens group is fixed as a whole and has an aperture in front of it or inside it closer to the object side. A movable lens group F having a negative refractive power and comprising a rear group and at least one negative lens having a surface of stronger curvature facing the image side than the aperture in the rear group. This system is characterized in that focusing toward a nearby object is performed by moving the group F toward the image side. The zoom lens system of the present invention is further characterized in that it satisfies the following conditions. 0.1<|fF|/f·γ<2 where fF is the focal length of the movable lens group in the rear group, f is the focal length of the rear group, and γ is the zoom ratio of the zoom lens. Next, the above conditions will be explained. The above conditions are
When focusing is performed using the movable lens group F in the rear group, this is necessary for correcting aberration fluctuations due to focusing in a well-balanced manner from the longest focal length L to the shortest focal length S by the variable magnification lens group. This is because the aperture is located in front of the rear group or closer to the object side in the rear group.
This is necessary also because the height of the off-axis light beam passing through the movable lens group F is high. In other words, if the lower limit of the above conditions is exceeded, the distance between the longest focal length L and the shortest focal length S
The balance of aberration correction across the range is disrupted, and it becomes difficult to correct aberrations during short-distance focusing at either focal length. On the other hand, if the upper limit of the above conditions is exceeded, the closest photographing distance at which focusing can be performed becomes longer, or the zoom ratio becomes smaller, making it difficult to construct a practical zoom lens system. Next, examples of the present invention will be shown.

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[Table] FIG. 1 shows the lens configuration at the longest focal length L of the first embodiment. Further, the straight line or curved line below shows the movement type of the lens group during zooming. In this embodiment, the focusing lens group F is composed of a positive and negative cemented lens. Second
The figure shows the object distance at infinity (D
=∞), the aberrations at the longest focal length L, intermediate focal length M, and shortest focal length S are shown. Furthermore, FIG. 3 shows aberration diagrams at each focal length of L, M, and S when the focusing lens group F is moved toward the image side and focused at D=5 m in Example 1. The maximum focal length L is 36.9 mm, and the shortest focal length S is 1.4 mm. FIG. 4 shows the lens configuration at the longest focal length L in Example 2 and the movement type of the lens group during zooming, and the focusing lens group F is composed of a positive and negative cemented lens. FIG. 5 shows the object distance at infinity (D=
∞) maximum focal length L, intermediate focal length M,
Each aberration at the shortest focal length S is shown. Furthermore, the sixth
The figure shows each aberration diagram at each focal length of L, M, and S when the focusing lens group F is moved toward the image side and focused at D=3 m in Example 2, and the amount of movement is the longest focal length. at distance L
It is 14.2mm, and the shortest focal length S is 1.7mm. FIG. 7 shows the lens configuration at the longest focal length L in Example 3 and the movement type of the lens group during zooming. The focusing lens group is composed of a positive and negative cemented lens and a negative lens. has been done. Figure 8 shows the object side distance at infinity (D=∞)
The aberrations at the longest focal length L, intermediate focal length M, and shortest focal length S are shown. Furthermore, Figure 9 shows that
Move the focusing lens group to the image side and
This shows the aberration diagrams at each focal length of L, M, and S when focusing at =3m.The amount of movement is 11.8mm at the longest focal length L and 11.8mm at the shortest focal length S.
It is 1.4mm. In this embodiment, in close-up photography, the shortest shooting distances for the longest focal length L and the shortest focal length S are made the same, but the shortest shooting distances for the longest focal length L and the shortest focal length S are not necessarily the same. do not have to. For example, regarding the lens of Example 1, the shortest focal length S is the focusing lens group F.
By moving 35.5 mm further toward the image side from the position D = 5 m, focusing becomes possible up to the shooting distance D = 0.5 m. Further, according to the present invention, the movable lens group F in the rear group includes at least one negative lens having a surface with a stronger curvature facing the image side. That is, the movable lens group F in Examples 1 and 2 consists of a cemented negative lens with a surface of stronger curvature facing the image side, and of the two lenses in the movable lens group F in Example 3, the negative lens on the image side is The curvature is stronger on the image side. This configuration is particularly advantageous in reducing fluctuations in spherical aberration during focusing. As is clear from the above, in the present invention, since the front group closest to the object side is fixed, there is no need to move it forward for focusing, and its effective diameter can be small. Since the group is freed from the burden of focusing, the degree of freedom in selecting its focal length increases, which is also advantageous for correcting aberrations. According to the present invention, as the focal length changes due to zooming, the amount of movement of the movable lens group F to the same shooting distance differs, but the movable lens group F is moved under the control of an electric signal such as an automatic focus detection signal. In the case of driving, the difference in the amount of movement can be detected electrically, so there is no problem. Rather, when driving the focusing lens group under the control of electrical signals,
It is advantageous that the driving source is located inside the camera body, that is, at the rear of the lens system, and in this case, it is extremely convenient for the focusing lens group F to be located at the rear of the lens system, close to the driving source. As described above, the present invention can provide a compact zoom lens system that is suitable for focus adjustment as a whole and has good aberration performance.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the lens configuration and lens movement type of the first embodiment of the present invention, FIGS. 2 and 3 are aberration diagrams of the first embodiment, and FIG. 4 is a second embodiment of the present invention. 5 and 6 are aberration diagrams of the second embodiment.
The figure is a sectional view showing the lens configuration and lens movement type of the third embodiment of the present invention, and FIGS.
It is an aberration diagram of an example. ...Front group, ...variable lens group, ...rear group, F...moveable lens group for focusing, S...
...Aperture.

Claims (1)

[Scope of Claims] 1. In order from the object side: a fixed front group, a variable magnification lens group that is movable for variable magnification, and a rear group that is fixed as a whole and has an aperture in front of it or inside it closer to the object side. and a movable lens group with a negative refractive power including at least one negative lens with a surface of stronger curvature facing toward the image side than the aperture in the rear group. A zoom lens system that performs focusing from infinity to a nearby object by moving the lens to the side, and satisfies the following conditions: 0.1<|fF|/f・γ<2 However, fF is in the above rear group. f is the focal length of the rear group; γ is the lens ratio of the zoom lens system. 2. The zoom lens system according to claim 1, wherein the variable power lens group includes a variator group and a compensator lens group in order from the object side.