JPS6356962B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a zoom lens system, and more particularly to a focusing device thereof. When moving one of the multiple lens groups for focusing in a zoom lens system, the driving distance (simply referred to as the focusing adjustment distance) of the lens group that is moved for focusing is the distance from the closest shooting distance to ∞. There are some things that change depending on the zoom operation. For example, in a so-called front focusing zoom lens, the amount of extension of the focusing lens group for focusing does not change even if the focal length is changed, but in a system where the focusing lens group is the rear group of the zoom lens system, for example, A four-component mechanically corrected zoom lens, consisting of a fixed first group, a movable second group for variable magnification, a movable third group for correction, and a fourth group for focusing.The fourth group is not driven during zoom operations. The focus adjustment distance is small at the wide end, where the focal length is short, and large at the telephoto end, where the focal length is long. If the focusing distance of the focusing lens group differs depending on the focal length as described above, the automatic focusing device should be configured so that it can operate with high precision and at an appropriate high speed at the shorter focusing distance. Even if the focus adjustment distance is long, the driving distance of the focusing lens group will be longer for the same change in shooting distance, so the lens group driving speed will be relatively insufficient and quick focusing will not be possible. Conversely, if the performance of the automatic focusing device is adapted to the longer focusing distance, the driving speed of the focusing lens group will be relatively too fast at the shorter focusing distance, and the inertia of the mechanism will increase. , play, etc. make it difficult to achieve accurate focusing. The present invention has been made with the object of solving the above-mentioned problems in zoom lens systems in which the focusing adjustment distance of the lens group driven for focusing changes depending on the focal length. The present invention changes the refractive power of the focusing lens group in conjunction with the zoom operation.
An object of the present invention is to provide a zoom lens system focusing device that reduces the difference in focus adjustment distance due to focal length. The present invention will be explained below with reference to Examples. FIG. 1 shows a paraxial lens configuration of a zoom lens system according to an embodiment of the present invention, where a shows a wide lens arrangement, b shows a medium focal length, and c shows a telephoto side lens arrangement. 1 is the first lens group, 2 is the second lens group, and 3 is the third lens group. Lens groups 1 and 3 are integrally moved back and forth in a linear relationship with respect to the focal length by zoom operation, and lens group 2 is moved back and forth in a curved functional relationship with respect to the focal length by zooming. Both 4a and 4b constitute an orcusing lens group, and in a conventional zoom lens of this type, 4a and 4b form an integrated group and are usually fixed during zoom operation. Focusing lens group 4a, 4b
A feature of the present invention is that the lens groups 4a and 4b are divided into groups, and the interval between the groups is changed in conjunction with the zoom operation.One of the lens groups 4a and 4b exhibits a positive refractive power and the other a negative refractive power, and the distance between them changes. As a result of the zoom operation, the refractive power of the focusing lens group as a whole changes depending on the focal length. The table below shows numerical values for the paraxial configuration of the lens system in FIG. In the table, φ1 to φ4b indicate the refractive powers of lens groups 1 to 4b, respectively, and e12 and the like indicate the distances between lens groups 1 and 2 in mm. f is the focal length, expressed in mm.

[Table] The combined refractive power φab of the focusing lens groups 4a and 4b is as shown in the table below. f 28 48.166 76.434 φab 0.00476 0.00499 0.00570 According to the conventional method, for example, focusing lens groups 4a and 4b have the distance relationship at f=28 in the previous table.
If eab=3.683 is fixed, in that case, the focusing adjustment distance for the shooting distance from 0.9m to ∞ on the telephoto side is
It becomes 20.81m. On the other hand, in the present invention, eab changes to 11.992 at the telephoto side, and the refractive power of the focusing lens group is stronger than when it is wide, so the focusing adjustment distance is compressed to 14.09mm, about 2/3 of the conventional configuration. It is becoming. FIG. 2 shows a drive mechanism for the lens configuration of FIG. The blocks surrounded by dotted lines are lens groups 1, 2, and 3.
The lens barrel holds the lens groups 1 to 3 so as to be slidable in the optical axis direction, and the cam grooves 6, 7, and 8 form pins 1 that protrude laterally from the lens frame of each lens group 1 to 3.
2, 13, and 14 are engaged. The solid line block 17 holds the focusing lens groups 4a and 4b slidably in the optical axis direction, and is also a lens barrel that is movable in the optical axis direction and is provided with cam grooves 9 and 10. , 4b are engaged with pins 15 and 16 protruding from the sides. 11 is a key groove provided in the inner surface of the zoom operation ring in the optical axis direction; pins 12, 13, 14, 15, and 16 passing through cam grooves 6, 7, 8, 9, and
Therefore, when the zoom operation ring is rotated, the lens groups 1 to 4b are engaged with the cam grooves 6, 7, and 8, respectively.
9 and 10, the distance relationship shown in the table above is realized. As described above, the lens barrel 17 holding the lens groups 4a and 4b is slidable in the optical axis direction and is connected to an automatic focusing device, and the lens groups 4a and 4b are integrated as a whole for focusing. It is driven forward and backward. Motor M is a pulse motor that is controlled by a signal from a focus detection circuit (not shown), and the rotation of motor M is transmitted to lens barrel 17 via a pinion and racks P and R. FIG. 3 shows another embodiment of the invention. The difference from the above embodiment is the distribution of refractive power of the fourth lens groups 4a and 4b. The table below shows the paraxial configuration of the lens in Figure 3. φ, e, and f have the same meanings as in the lens system data of FIG.

【table】

[Table] The combined refractive power of lens groups 4a and 4b is as shown in the table below. φfb 26.5 45.85 75.04 φab 0.00652 0.00668 0.00681 In this embodiment, the amount of movement of the positive lens group 4a of the focusing lens group during the zoom operation is extremely small. The drive mechanism for each lens group has the same structure as that shown in FIG. 2, but the cam groove 9 for the lens group 4a is not required and processing costs can be reduced. The zoom lens focusing device of the present invention has the above-described configuration, and the lens group driven for focusing is divided into two groups, and the distance between the two groups is changed in conjunction with the zoom operation, and the combined refractive power is adjusted to the focal length. Since the difference in focusing adjustment distance due to focal length is reduced by changing the focusing distance, when combined with an automatic focusing device, focusing can be performed with the same speed and precision at any focal length. . In the above embodiment, the focusing lens group is composed of only two groups, but it goes without saying that the focusing lens group may be composed of three or more groups.

[Brief explanation of the drawing]

FIG. 1 is a side view showing the paraxial configuration of a zoom lens system in one embodiment of the present invention, FIG. 2 is a side view of the drive mechanism of the lens group, and FIG. 3 is a zoom lens system in another embodiment of the present invention. FIG. 3 is a side view showing a paraxial configuration of the lens system. 1, 2, 3... Lens group, 4a, 4b... Focusing lens system, 6, 7, 8, 9, 10...
Cam groove, 11...key groove.

Claims (1)

[Claims] 1. In a zoom lens system that includes a focusing lens group behind a lens group that moves for zooming, the focusing lens group is composed of a plurality of groups whose intervals can be changed. Each group of the focusing lens system is adjusted according to zooming so that the combined refractive power of the focusing lens group at the shortest focal length is smaller than the combined refractive power of the focusing lens group at the longest focal length. A zoom lens system that is characterized by changing the interval between lenses and moving the focusing lens group as a unit while keeping the other groups stationary during focusing.