JPH0119121B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focusing device for a zoom lens group suitable for automatic focusing.

When moving one of the multiple lens groups for focusing with a zoom lens, the driving distance (simply referred to as the focusing adjustment distance) of the lens group moved for focusing from the closest shooting distance to infinity. Alternatively, the driving range changes depending on the zooming operation. Therefore, the movable range of the lens group driven for focusing needs to be larger than the focusing adjustment distance at each focal length. However, when the movable range of the lens group is wider than the focusing adjustment distance, various difficulties arise when performing automatic focusing as described below.

In order to clarify the purpose and features of the present invention, one or two examples of zoom lens focusing methods will be described. The example shown in Figure 1 has four lens groups 1, 2,
A zoom lens consisting of 3 and 4 lenses, where a indicates a short focal length (wide), b indicates a medium focal length, and c indicates a long focal length (tele). 5 is the film surface. In a zoom operation, lens groups 1 and 3 move back and forth integrally, and lens group 2 is driven with a certain functional relationship with respect to lens groups 1 and 3. The lens group 4 usually does not move due to zoom operation. This is a type called a four-component mechanically corrected zoom lens. In this method, focusing is performed by moving lens group 4 or a part of lens group 4 and lens group 3 back and forth. Lens group 4 in the diagram
indicates the position adjusted to the distance ∞, the dotted line S is a curve that connects the position of lens group 4 with respect to the most recent shooting distance, and x in the figure is the focusing adjustment distance of lens group 4 at an arbitrary focal length. . As you can see from the figure, the focusing adjustment distance is small on the wide side and large on the telephoto side, so at least the focusing adjustment distance xo on the telephoto side is required for the movable range of lens group 4. , this is an unnecessarily wide range for medium focal lengths or wide-angle lenses. FIG. 3 shows a type of zoom lens in which two lens groups 13 and 14 are moved in a certain functional relationship with each other by a zoom operation, and focusing is performed by moving the lens group 13 back and forth. In the same figure, a is telephoto, b is medium focal length,
c shows a wide-angle state, and each lens group 13 shows a case where the shooting distance is ∞. In this case, the amount of movement of the lens group 13 from ∞ to the most recent shooting distance (focusing adjustment distance) is the same from wide to telephoto, but the movable range of the lens group 13 is from the ∞ position at wide to the most recent shooting at telephoto. XO is required to reach the distance position, which is extremely wide compared to the focusing adjustment distance.

Two problems can be expected from the above example. One of these problems is that the focusing distance changes depending on the zoom operation, that is, depending on the focal length. The second problem is that even if the focus adjustment distance does not change due to the zoom operation, the movable range of a certain lens group becomes larger than the focus adjustment distance due to the movement for the zoom operation. First of all, if the focusing adjustment distance differs depending on the focal length (as in the example in Figure 1 above), if the performance of the automatic focusing device is adapted to the case of a wide-angle lens with a short focusing distance, it is possible to Focusing speed is relatively slow at the telephoto side, and conversely, if you adjust the performance of the automatic focusing device to the telephoto side, where the focusing distance is long, it will be difficult to obtain sufficient focusing accuracy at the wide side. . This is a problem caused by the inertia and precision of the mechanism or motor. Next, if the movable range of the lens group is larger than the focusing adjustment distance, for example, the third
In the example shown in the figure, the automatic focusing device moves the lens group 13 within the range of The automatic focusing device starts from the St position and moves the lens group 13 to a certain photographing distance. At this time, the image is significantly out of focus at the St position of the lens group 13, and various currently known automatic focusing devices cannot determine in which direction the lens group 13 should be moved to bring it closer to the in-focus state. Therefore, in cases like this, the automatic focusing device cannot operate smoothly. A similar problem occurs in the case of Fig. 1 when the focus is switched to wide after focusing on a short distance in telephoto mode. Such troubles arise when the automatic focusing device is programmed with a specific program that always returns the focusing lens group to the ∞ position and then moves it toward the near distance side. However, if you do this, the focusing lens group will return to the ∞ position one by one every time you change the subject, impeding the speed of camera operation.

The present invention was made primarily to solve the latter problem mentioned above. In other words, in order to solve the problem that the movable range of the lens group is larger than the focusing adjustment distance, in the present invention, the movable range of the lens group is adjusted in conjunction with the zoom operation for the lens group that is driven for focusing. An electrical regulating means is provided so that the distance becomes the focusing adjustment distance at the focal length at that time. In this way, even if a zoom operation is performed arbitrarily, the lens group for focusing is always within the range of the focusing adjustment distance, so that the automatic focusing device can always operate smoothly.

FIG. 2 is a diagram illustrating the operation when the present invention is applied to the zoom lens system shown in FIG. 1.
Numerals 6, 7, and 8 are cam grooves, and by zooming, lens group 1 is integrally moved back and forth along the cam groove, lens group 3 is integrally moved forward and backward along the cam groove 8, and lens group 2 is moved along the cam groove 7. It is moved back and forth to perform a correction operation. The lens group 4 is a lens group that is moved for focusing, and its position with respect to the shooting distance ∞ does not change due to the zoom operation. 5 is a focal plane. Reference numeral 12 denotes a regulating member in the case where the movable range of the lens group 4 is mechanically limited. The cam grooves 6, 7, 8 and the regulating member 12 are provided in one lens barrel, and the regulating member 12 forms an opening 11 that is narrow on the wide side and wide on the telephoto side, and the right edge 10 of this opening is aligned with the ∞ position of the lens group 4, and the left edge 9 is aligned with the position of the lens group 4 with respect to the closest photographing distance, for example, 1 m. A pin is set up on the side of the frame of each lens group 1 to 4, and the pin passes through the corresponding cam grooves 6, 7, 8 and opening 11, and forms a straight line in the front-rear direction of the inner surface of the zoom operation ring on the outside of the lens barrel. engaged in the groove. For example, when this straight groove is at the position indicated by the two-dot chain line in FIG. . When a zoom operation is performed to the wide-angle side from a state in which the lens system is adjusted to a close distance on the telephoto side, the lens group 4 is pushed by the left edge 9 of the member 12 and is forced to retreat to the right. The present invention attempts to electrically implement the regulation by the regulation member 12 described above. Since the lens group 4 is also connected to the automatic focusing device, a slippable frictional connection is preferably provided between the lens group 4 and the automatic focusing device.

In Figure 2, each refractive power φ of the first to fourth lens groups
1 to φ4, paraxial distance e1 between the first and second lens groups
2. Paraxial distance e23 between the second and third lenses, third,
Paraxial distance e34 between the fourth lenses, composite focal length f
etc. are as shown in the table below.

φ1 0.00683 e12 (mm) 6.9~25.01~37.94 φ2 0.02757 e23 (mm) 49.83~31.72~
18.79 φ3 0.02098 e34 (mm) 17.84~37.15~
62.77 φ 4 0.00494 f (mm) 35.05~60.851~100.37 Also, the extension amount of lens group 4 from the shooting distance ∞ to 1.2m is f 35.05~60.851~100.37 Extension amount 2.3~6.8~17.3, and the zoom ratio The ratio of the payout amount of 2.86 times is approximately 7.5 times.

FIG. 4 is a diagram illustrating the operation when the present invention is applied to the zoom type lens system shown in FIG. 3. 15 is a zoom operation cam groove for the lens group 14. As in FIG. 2, reference numeral 12 is a regulating member for performing mechanical regulation, and is provided on the same cylinder as the cam groove 15, and has a cam groove-shaped opening 16 having a width d. The lens groups 13 and 14 are moved together by the zoom operation, but the lens group 13 has a degree of freedom in position within the range of the width d of the aperture 16 of the regulating member 12, and this range is the focusing adjustment distance at each focal length state. In this range, the lens group 13 is driven by the automatic focusing device for focusing.

FIG. 5 shows an embodiment of the present invention. This embodiment is applied to a zoom lens system of the type shown in FIG. M is a drive motor for the lens group 4 for automatic focusing, and drives a gear G that meshes with a rack fixed to the frame of the lens group 4 in the forward and reverse directions. P is a pulse generation circuit that drives the motor M, which outputs a forward rotation pulse or a reverse rotation pulse in response to a signal from a focus detection circuit C, and stops generating pulses when a focus signal is input. The lens group 4 is provided with a sliding contact piece r, which can come into sliding contact with a printed conductor piece 12' formed on the inner surface of the lens barrel. Conductor piece 1
2' is connected to a power source via a resistor R, and is grounded when the sliding contact piece r comes into contact with it. The potential of the conductor piece 12' is sent to the pulse generating circuit P, and when the same potential is high, that is, when the sliding contact piece r is not in contact, the pulse generating circuit P is controlled by the signal from the focus detection circuit C, and the sliding contact is not made. When the piece r is in contact and the potential is 0, the pulse generating circuit P outputs a reverse pulse to drive the lens group 4 to the right ∞ side. The right edge of the conductor piece 12' has the same shape as the left edge 9 of the opening 11 of the regulating member 12 in FIG. Therefore, at this time, the driven sliding contact piece r is connected to the conductor piece 1.
The lens group 4 is driven to the right until it separates from 2'.
After that, it is controlled by the signal from the focus detection device. The above-mentioned embodiment is one in which the present invention is applied to the lens configuration shown in FIG.
Needless to say, the present invention can also be applied to the lens configuration shown in the figure.

The zoom lens focusing device according to the present invention has the above-described configuration, and since the lens group driven for focusing is always within the range of the focusing adjustment distance, the automatic focusing device can be used even when performing arbitrary zoom operations. can always operate reliably.

[Brief explanation of drawings]

Fig. 1 is a side view showing the lens arrangement of an example of a zoom lens system, Fig. 2 is a side development view for explaining the operation of an example of the present invention, and Fig. 3 is a side view showing the lens arrangement of another example of the zoom lens system. FIG. 4 is a developed side view for explaining the operation of another example of the present invention, and FIG. 5 is a block diagram showing an embodiment of the present invention. 1, 2, 3, 4... Lens group, 6, 7, 8... Cam groove, 12... Regulating member, 13, 14... Lens group, 1
5...Cam groove, M...motor, G...gear, P...pulse generation circuit, C...focus detector, 12'...conductor piece, r
...Sliding contact piece.

Claims (1)

[Claims] 1. In a zoom lens that requires changing the focus adjustment range of a lens group driven for focusing in conjunction with zoom operation, a signal indicating whether the lens group is within the focus adjustment range is provided. A signal output member that outputs signals according to the zoom operation and the position of the lens group, a focus detector that detects the in-focus state of the lens group, a motor that conductively drives the lens group, and when the lens group is within the focus adjustment range. If a signal indicating that the lens group is outside the focusing range is output from the signal output member, the motor is driven based on the output of the focus detector, and if a signal indicating that the lens group is outside the focusing range is output. A focusing device for a zoom lens, comprising: motor control means for driving the motor toward a focusing range.