Interchangeable lens video camera system having improved focusing

• US 6,683,652 B1
• Filed: 08/26/1996
• Issued: 01/27/2004
• Est. Priority Date: 08/29/1995
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Suda, Hirofumi, Ohkawara, Hiroto
• Primary Examiner(s): Vu, Ngoc-Yen, VU, NGOC YEN T
• Application Number:
  US08/703,902
• Time in Patent Office: 2,710 Days
• Field of Search: H04/N.5238, H04/N.5232, 348/226, 348/229, 348/345, 348/347, 348/207, 348/222.1, 348/223.1, 348/224.1, 348/225.1, 348/226.1, 348/228.1, 348/229.1, 348/211.14, 348/348-351, 348/354-356, 348/360-364, 396/89, 396/81, 396/86, 396/529
• US Class Current: 348/347
• CPC Class Codes: H04N 23/635 Region indicators; Field of view indicators
• CPC Class Codes: H04N 23/663 for controlling interchangeable camera parts based on electronic image sensor signals
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method
• CPC Class Codes: H04N 23/72 Combination of two or more compensation controls

Abstract

An interchangeable lens video camera system which can stably focus on a main target object under any conditions of the object or the environment. The camera system includes a lens assembly detachably attached to a camera for photoelectrically converting incident light to sense an image and output an image signal. The camera system further includes a zoom lens and a focus lens controlled on the basis of an automatic focus evaluation value and data associated with exposure which are received from the camera while referring to a lens cam data unit which stores locus information of the zoom lens and the focus lens in advance. The interchangeable lens video camera system allows for the reduction of blurring and degradation of image quality.

Claims

1. A lens assembly detachably attached to a camera having image sensing means for sensing an image of an object and outputting an image signal, comprising:

a variable power lens for performing a zooming operation;

a focus lens for performing a focusing operation and compensating for a movement of an in-focus point caused by the zooming operation of said variable power lens;

memory means for storing position information of said variable power lens and said focus lens;

focus detection means for receiving an evaluation value associated with an image sensing state of an object from the image signal outputted from said camera and extracting, from the received image signal, an evaluation value which changes in accordance with a focus state; and

control means for controlling said variable power lens and said focus lens on the basis of the position information stored in said memory means and the evaluation value associated with the image sensing state obtained by said focus detection means.

2. The lens assembly according to claim 1, wherein the image signal is normalized in accordance with the focus state.

3. The lens assembly according to claim 1, wherein said focus detection means extracts a high-frequency component contained in the image signal.

4. The lens assembly according to claim 1, wherein said focus detection means extracts only an image signal corresponding to an area for distance measurement from the image signal.

5. The lens assembly according to claim 1, wherein said memory means stores design position information of said variable power lens and said focus lens in advance and said control means further comprises adjusting means for adjusting an operation of said focus lens on the basis of the position information to compensate for a movement of an in-focus point caused by the zooming operation of said variable power lens.

6. The lens assembly according to claim 5, wherein said adjusting means adjusts an operation stroke of said variable power lens to change a telephoto end position and a wide end position.

7. The lens assembly according to claim 6, wherein said adjusting means calculates a position of said variable power lens, at which an in-focus position of said focus lens and a moving amount of said focus lens from the telephoto end position equal those of the design position information, thereby changing the telephoto end position and the wide end position.

8. An interchangeable lens video camera system constituted by a camera and an interchangeable lens assembly,

wherein said camera comprises image sensing means for photoelectrically converting incident light to sense an image and transmitting an image signal to said lens assembly, and

said lens assembly comprises

a variable power lens for performing a zooming operation;

a focus lens for performing a focusing operation and compensating for a movement of an in-focus point caused by the zooming operation of said variable power lens;

memory means for storing position information of said variable power lens and said focus lens;

focus detection means for receiving the image signal outputted from said camera and extracting, from the image signal, evaluation information which changes in accordance with a focus state; and

control means for controlling said variable power lens and said focus lens on the basis of the position information stored in said memory means and the evaluation information obtained by said focus detection means.

9. The system according to claim 8, wherein said camera further comprises normalizing means for normalizing the image signal output from said image sensing means in accordance with an image sensing state.

10. The system according to claim 8, wherein said focus detection means extracts a high-frequency component contained in the image signal.

11. The system according to claim 8, wherein said focus detection means extracts only an image signal corresponding to an area for distance measurement from the image signal.

12. The system according to claim 8, wherein said camera further comprises first switch means for turning on/off an operation of said focus detection means.

13. The system according to claim 8, wherein said memory means stores design position information of said variable power lens and said focus lens in advance and said control means further comprises adjusting means for adjusting an operation of said focus lens on the basis of the position information to compensate for a movement of an in-focus point caused by the zooming operation of said variable power lens and said camera further comprises second switch means for turning on/off an operation of said adjusting means.

14. The system according to claim 13, wherein said adjusting means adjusts an operation stroke of said variable power lens to change a telephoto end position and a wide end position.

15. The system according to claim 14, wherein said adjusting means calculates a position of said variable power lens, at which an in-focus position of said focus lens and a moving amount of said focus lens from the telephoto end position equal those of the design position information, thereby changing the telephoto end position and the wide end position.

16. A lens assembly detachably attached to a camera having image sensing means for sensing an image of an object and outputting an image signal, comprising:

a variable power lens for performing a zooming operation;

a focus lens for performing a focusing operation and compensating for a movement of an in-focus point caused by the zooming operation of said variable power lens;

first memory means for storing position information, which is determined in advance, of said variable power lens and said focus lens;

control means for controlling said variable power lens and said focus lens on the basis of the position information stored in said first memory means; and

second memory means for storing current position information of said variable power lens and/or said focus lens,

wherein said control means stores, when a power supply of said lens assembly is turned off, current position information in said second memory means, and

said control means determines, upon turning on said power supply, whether a camera to which said lens assembly is mounted is the same as that in a previous operation, and if said camera is the same as that in the previous operation, said control means restores an operation state of said variable power lens and/or said focus lens at the time of turning off said power supply on the basis of the latest current position information stored, when said power supply is turned off, in said second memory means.