JP2776030B2 - Zoom drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving apparatus for a zoom lens in a video movie.

[0002]

2. Description of the Related Art In recent years, with the spread of video movies, high performance has been achieved by employing an inner focus type zoom lens which is small and lightweight and can autofocus from immediately before the lens to infinity.

In the inner focus type zoom lens, if the focusing lens is not instantaneously moved to a predetermined position in accordance with the position of the variable power lens, a focus shift occurs, and a very difficult-to-view screen is obtained. Therefore, there is a demand for a small and lightweight zoom driving device that has no out-of-focus, has high zoom tracking accuracy, and has high accuracy.

Hereinafter, a conventional zoom driving device will be described with reference to the drawings. FIG. 2 is a sectional view showing a configuration of a conventional zoom driving device. In the figure, a lens group is composed of a first group lens 1, a second group lens 2, a third group lens 3 and a fourth group lens 4, wherein the second group lens 2 is a variable power lens and the fourth group lens 4 is a focusing lens. The first lens group 1 and the third lens group 3 are held by the lens barrel body 5. The second group lens 2 is held by the second group moving frame 6. A female screw is provided in the hole 6 a of the frame 6 and is engaged with the feed screw 7. The feed screw 7 is rotatably held by the lens barrel body 5 and is driven to rotate by a zoom motor 8 via a gear 7a and a gear 8a. A zoom encoder 9 for detecting the position of the second group lens is fixed to the lens barrel main body 5, and a convex portion 9 a thereof is engaged with the moving frame 6. Fourth group lens 4 is fourth group moving frame 1
It is kept at 0. It is held by the lens barrel body 5 with a guide pin 11 that engages with the hole 10 a of the frame 10, and engages with the projection 12 a of the focus motor 12.

The operation of the above configuration will be described. When the electric zoom switch is pressed, the zoom motor 8 is driven, the feed screw 7 is rotated via the gears 8a and 7a, and the second group lens 2 is moved in the wide direction (W direction) or the telephoto direction (T direction).
At a constant speed. The position is detected by the zoom encoder 9. Further, the moving frame 10 is moved by the rotation of the focus motor 12 while being held by the guide pins 11, and the fourth lens group 4 is moved. FIG. 3 is a graph showing the relationship between the position of the focusing lens and the position of the zoom lens.
The focusing state during zooming is ensured by moving the focusing lens in the relationship shown in the graph.

[0006]

In such a conventional zoom driving device, the inclination of the tracking curve shown in FIG. 3, that is, the ratio Δf / Δv of the movement amount of the zoom lens to the movement amount of the focusing lens is at the telephoto end. There is a large relationship in the vicinity, and it is difficult to move the fourth lens unit 4 following the movement of the second lens unit 2. When not followed, a focus shift occurs, and the screen becomes very difficult to see. FIG. 4 shows the moving speed required to move the fourth group lens during zooming, using the moving time of the second group lens (moving time between W and T) as a parameter. When a stepping motor is used as a focus motor for moving the fourth lens group, the moving speed limit is determined by noise, vibration, and step-out. In FIG. 4, the moving time of the second group lens is 6
In the case of sec, tracking is possible within the speed limit of the focusing lens in the range from point W to point A in the figure, but is impossible in the range from point A to telephoto end T. If the movement time of the zoom lens is designed to be as slow as 12 seconds as shown by a broken line in the drawing, for example, as shown by a broken line in the drawing, the focusing lens can follow. However, there is a disadvantage that the zoom operation on the subject becomes slow.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a zoom driving device having good tracking performance of zoom tracking without lowering the zoom speed.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a lens barrel body for holding a fixed lens, a variable power lens holding frame for holding a variable power lens, and the variable power lens holding frame. A feed screw for moving the feed screw back and forth in the lens barrel, a means for rotating the feed screw, a position detecting means for detecting a position of the variable power lens, a focusing lens for focusing on an imaging surface, and a focusing lens. In the inner focus type zoom lens provided with a means for moving a single lens, a pitch of the feed screw is continuously changed in an axial direction, and a moving speed of the variable power lens changes corresponding to the position. A zoom drive device having a feed screw, and a zoom drive set by changing the feed screw pitch so that the moving speed of the focusing lens is within the moving speed limit. And location.

[0009]

According to the present invention, in the above arrangement, the feed screw set by changing the pitch moves the variable power lens at a different speed, and the variable speed is adjusted so that the moving speed of the following focusing lens is within the speed limit. The lens moves. (At the zoom lens position where the following speed of the focusing lens becomes faster, the moving speed of the zoom lens is reduced.)

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a zoom drive device according to one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing the configuration of a zoom drive device according to an embodiment of the present invention. In the figure, the lens groups are group 1 lens group 21, group 2 lens 22,
The second lens group 22 is a variable power lens, and the fourth lens group 24 is a focusing lens. The first lens group 21 and the third lens group 23 are held by the lens barrel body 25. The second group lens 22 is held by the second group moving frame 26. The frame 26
The feed screw 29 is inserted into the hole 26a. Feed screw 2
The lens 9 is rotatably held by the lens barrel main body 25, and is driven to rotate by the zoom motor 31 via a gear 29a and a gear 31a. Zoom encoder 3 for detecting the position of the second group lens
Reference numeral 0 is fixed to the lens barrel main body 25, and the convex portion 30 a is engaged with the moving frame 26. The fourth group lens 24 is held by the fourth group moving frame 32. The frame 32 is held by the lens barrel main body 25 by guide pins 33 that engage with the holes 32a, and engages with the projections 34a of the focus motor 34. In the present invention, the pitch of the feed screw 29 is continuously set smaller as it goes to the T side. Further, a steel ball 28 and a pressing spring 27 for pressing the steel ball 28 against the feed screw 29 are provided in the hole of the moving frame 26. The steel ball 28 engages with a thread recess of the feed screw 27.

The operation of the above configuration will be described. In the figure, when the switch of the electric zoom is pressed, the zoom motor 31 is driven and the gears 31a and 29a are used to drive the feed screw 29.
Rotates to move the second lens group 22 in the wide direction or the telephoto direction. The position is detected by the zoom encoder 30. Further, the moving frame 32 is moved by the rotation of the focus motor 34 while being held by the guide pins 33 to move the fourth group lens 24. Also in this case, the relationship between the position of the focusing lens and the position of the zoom lens needs to satisfy the relationship shown in the graph of FIG. In the present invention, by reducing the pitch of the feed screw 29 on the T side to slow down the moving speed of the second group lens 22, the necessary moving speed of the fourth group lens 24 is set to a value as shown by a dashed line in FIG. , And it becomes possible to follow within the conventional moving speed limit. In this case, the moving speed of the variable power lens is set to be slow only at a part of the T-side end, and can be set to be higher than the conventional moving speed in most of the moving range, so as to utilize the limit speed of the focusing lens.

As described above, according to the zoom driving apparatus of one embodiment of the present invention, the pitch of the feed screw of the variable power lens is set by changing it according to the lens position, and the moving speed of the focusing lens is within the limit. By setting the moving speed of the variable power lens in such a manner, the moving speed of the focus lens can be utilized to the limit and a highly accurate focus trace can be performed.

[0013]

As is apparent from the above embodiments, the present invention provides a lens barrel body for holding a fixed lens, a variable power lens holding frame for holding a variable power lens, and A feed screw for moving the feed screw back and forth in the body, a means for rotating the feed screw, a position detecting means for detecting a position of the variable power lens, a focusing lens for focusing on an imaging surface, and moving the focusing lens An inner focus type zoom lens provided with a means for causing the feed screw to be provided with the pitch of the feed screw continuously changed in the axial direction, and the moving screw of which the moving speed of the variable magnification lens changes corresponding to the position. And the moving speed of the zoom lens is set so that the moving speed of the focusing lens that follows the movement of the zoom lens is within the limit moving speed. With the zoom drive having a Rineji pitch, by utilizing the moving speed of the focus lens to the limit, it is highly accurate focus trace.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a zoom driving device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a conventional zoom driving device.

FIG. 3 is a graph showing a positional relationship between a variable power lens and a focus lens in a focused state.

FIG. 4 is a graph showing the speed at which the focus lens should move in accordance with the position of the zoom lens.

Claims (2)

(57) [Claims] 1. A lens barrel main body for holding a fixed lens, a variable power lens holding frame for holding a variable power lens, a feed screw for moving the variable power lens holding frame back and forth in the lens barrel, and An inner focus type zoom lens including a means for rotating a screw, a position detecting means for detecting a position of the variable power lens, a focusing lens for focusing on an imaging surface, and a means for moving the focusing lens. A zoom drive device comprising the feed screw, wherein the pitch of the feed screw is continuously changed in the axial direction, and the moving speed of the variable magnification lens changes in accordance with the position. 2. The zoom driving device according to claim 1, wherein the zoom screw has a feed screw pitch in which the moving speed of the variable power lens is set so that the moving speed of the focusing lens that follows the movement of the variable power lens is within the limit moving speed.