JPH04145420A - Focus lens driving device for manually focusing lens system - Google Patents

Abstract

PURPOSE:To make quick manual focusing by driving a focus lens at a high speed when a depth of field obtained from a storing section on the basis of a detected focal distance is larger and at a low speed when the depth of field is smaller. CONSTITUTION:An f- and F-values detected by means of a focal distance (f- value) detector 13 and stop value (F-value) detector 14 are respectively converted into digital values by means of the 1st and 2nd A/D converters 16 and 17 and compared with f- and F-values stored in a ROM 18. The ROM 18 stores the optimum focus lens driving speeds against the depth of field at each subject distance in addition to the f- and F-values and a motor drive circuit 15 drives a focusing motor 11 on the basis of the optimum focus lens driving speed read out from the ROM 18. Since the f- and F-values and the relations between subject distances and depths of field are stored in the ROM 18, the circuit 15 can always obtain the optimum focus lens driving speed from the ROM 18.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lens system used in a video camera, and more particularly to a focus lens drive device used during manual focusing of the lens system.

[Prior Art] FIG. 3 is a cross-sectional view schematically showing an example of a conventional lens system for a video camera.

The lens system 1 includes a manual focus ring 2. A front lens 3, which is a focus lens, is provided within the focus ring 2.

Furthermore, the lens system 1 includes a variator 5. which is a zoom lens provided within the cam barrel 4. A compensator 6, an erector 7, and an iris (aperture) 8, which are lenses for correcting focus shifts due to zooming. and master lens 9, and the image to be shot is CCD10.
imaged on top.

In such a lens system, when the focus ring 2 is rotated, the front lens 3 moves back and forth along the optical axis of the lens system 1. Therefore, in conventional manual focusing, the photographer moves the front lens 3 by rotating the focus ring 2 by hand, and selects the optimum position of the front lens 3 for focusing through a viewfinder (not shown). can be found.

[Problems to be Solved by the Invention] However, since the photographer does not have appropriate information about the depth of field during manual focusing, in order to carefully observe the change in focus on the viewfinder, Try to move the focus lens 3 slowly. Therefore, with conventional manual focusing, it takes a considerable amount of time to reach the in-focus point.

In view of the problems of the prior art, an object of the present invention is to provide a focus lens drive device that enables rapid manual focusing.

[Means for Solving the Problems] According to the present invention, a focus lens drive device for manual focusing of a lens system includes an aperture value detection means for detecting the current aperture value of the lens system, and an aperture value detection means for detecting the current aperture value of the lens system. A focal length detection means for detecting the current focal length, a focus lens driving means for driving the focus lens in the lens system in a direction along the optical axis of the lens system, and a driving speed of the focus lens driving means. The drive speed control means includes a storage section that stores depths of field corresponding to various combinations of aperture values, focal lengths, and subject distances, and The focus lens drive means is configured to drive the focus lens at high speed when the depth of field obtained from the storage section is deep based on the aperture value detected by the value detection means and the focal length detected by the focal length detection means. When the depth of field obtained from the storage section is shallow, the focus lens driving means is controlled to drive the focus lens at a low speed.

[Function] In the focus lens driving device according to the present invention, based on the aperture value detected by the aperture value detection means and the focal length detected by the pointless distance detection means, the storage unit in the drive speed control means It is possible to know the depth of field. The drive speed control means controls the focus lens drive means to drive the focus lens at low speed when the depth of field is shallow, or to enable careful focusing when the depth of field is deep. Rapid manual focusing is made possible by controlling a focus lens driving means to drive the lens at high speed.

That is, the focus lens driving device according to the present invention has the following features:
It is possible to eliminate wasted time in manual focusing of conventional lens systems.

FIG. 1 of the second embodiment shows an example in which a focus lens driving device according to an embodiment of the present invention is applied to a lens system for a video camera. Lens system 1 has focus ring 2
The focus link 2 can be driven by a focusing motor 11. A front lens 3, which is a focus lens, is provided within the focus ring 2. A cam barrel 4 provided with a variator 5 serving as a zoom lens can be driven by a zoom motor 12 .

A convencator 5, which is a lens for correcting a focus shift due to zooming, is also provided within the cam barrel 4. Furthermore, the cam barrel 4 is associated with an f-number detector 13 that detects the focal length (f). An erector 6 and an iris (aperture) are provided at the rear of the cam cylinder 4, and the iris is associated with an F value detector 14 that detects an aperture value (F). A master lens 9 is provided behind the iris, and images from the lens system 1 are captured by a CCD.
The image is formed on l0.

f detected by the f-number detector 13 and the F-number detector 14
The value and F value are converted into digital values by first and second analog/digital (A/D) converters 16 and 17, respectively, and compared with the f value and F value stored in ROM 18. The ROM18 also stores the optimum focus lens drive speed for the depth of field determined by the f-number, F-number and subject distance, and the motor drive circuit 15 stores the optimum focus lens drive speed derived by the ROM18. The focusing motor 11 is driven based on this.

Figures 2A and 2B show the f-number of the lens system.

This is a graph showing the relationship between the F value, subject distance, and depth of field, where the horizontal axis represents the distance from the lens system to the subject, and the vertical axis represents the depth of field. Fig. 2A shows the case of f”10mm, and Fig. 2B shows the case of f=10mm.
The case of 0 mm is shown. As can be seen from these figures, depth of field has the following properties (1) to (3).

(1) The smaller the f-number, the deeper the depth of field.

(2) The larger the F number, the deeper the depth of field.

(3) The farther away from the subject, the deeper the depth of field.

That is, such f-number, F-number, and the relationship between subject distance and depth of field are stored in the ROM 18, and the motor drive circuit 15 can always know the optimal focus lens drive speed from the ROM 18. .

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a focus lens drive device that enables rapid manual focusing in a lens system.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a focus lens driving device according to an embodiment of the present invention. FIGS. 2A and 2B are graphs showing the relationship between focal length, aperture value, subject distance, and depth of field. FIG. 3 is a cross-sectional view showing an example of a lens system for a video camera. In the figure, 1 is a lens system, 2 is a focus ring, 3 is a front lens, 4 is a cam tube, 5 is a variator, 6 is a compensator, 7 is an erector, 8 is an iris, 9 is a master lens, 10 is a CCD, and 11 is a focusing motor,
12 is a zoom motor, 13 is an f-number detector, 14 is an F-number detector, 15 is a motor drive circuit, and 16 is a first A/'
D converter, 17 is the second A/D converter, and 18 is R
Indicates OM. In each figure, the same reference numerals indicate the same contents or corresponding parts. Patent applicant Sharp Co., Ltd. agent Patent attorney Kube Fukami, ゛・ (and 2 others) -332゛- Figure 1 1: Lens system 2: Lens system 2: Lens system 7 3; hq Ball 4: Power Otsuka 5: Ba') Hai-ta 6: Lo〉Go〉Jin 7: EU2 Ri8; Iris A9 Near Star L'/N°゛+O: CCD Fig. 2A Fig. 2B

Claims (1)

[Claims] A focus lens driving device for manual focusing of a lens system, comprising: aperture value detection means for detecting a current aperture value of the lens system; a focal length detection means for sensing; a focus lens driving means for driving a focus lens in the lens system in a direction along an optical axis of the lens system; and controlling a driving speed of the focus lens driving means. and a drive speed control means, the drive speed control means including a storage unit storing depths of field corresponding to various combinations of aperture values, focal lengths, and subject distances,
When the depth of field obtained from the storage section is deep based on the aperture value detected by the aperture value detection means and the focal length detected by the focal length detection means, the focus lens is driven at high speed. A focus lens driving device, comprising: controlling the focus lens driving means, and controlling the focus lens driving means so as to drive the focus lens at a low speed when the depth of field obtained from the storage section is shallow. .