Auto-focus system

1. An auto-focus system comprising:

a picture-taking lens device detachably attached to a camera via a mount;

a focus controlling device on the picture-taking lens device for setting an AF area in a display of a view finder of the camera and controlling a focus of a picture-taking lens to focus on an object in the AF area;

a view finder controlling device for controlling the display of the view finder displaying an image taken by the camera;

an AF area display information outputting device on the camera for outputting AF area display information for displaying AF area information relating to a range of the AF area;

an AF area indicating device for indicating a range of an AF area in the display of the view finder;

an AF area changing device for changing a range of an AF area to be set in the focus controlling device to a range of an AF area indicated by the AF area indicating device; and

a switching device for switching a change of a range of an AF area by the AF area changing device between possible and impossible, wherein the change at least relates to the location of an AF area, and wherein the switching device switches a change of a range of an AF area to impossible when the view finder controlling device has no function of displaying the AF area information on the view finder,

wherein said focus controlling device on the picture-taking lens device performs a test to determine if the AF area display information outputting device has requested AF area display information from the focus controlling device, and

if the AF area display information outputting device on the camera has requested that the focus controlling device send AF area display information to the AF area display information outputting device, then the focus controlling device determines whether or not that said camera has a function of displaying the AF area information on the view finder, and

if the AF area display information outputting device has not requested that the focus controlling device send AF area display information to the AF area display information outputting device, then the focus controlling device determines that said camera has no function for displaying the AF area information on the view finder.

2. The auto-focus system according to claim 1 , wherein when the view finder controlling device does not receive AF area display information from the AF area display information outputting device, the switching device determines that the view finder controlling device has no function of displaying the AF area information on the view finder.

3. The auto-focus system according to claim 2 , wherein when the switching device makes a change of a range of an AF area impossible, at least the location of an AF area set by the focus controlling device is fixed to a predetermined location.

4. The auto-focus system according to claim 1 , wherein when the switching device makes a change of a range of an AF area impossible, at least the location of an AF area set by the focus controlling device is fixed to a predetermined location.

5. The auto-focus system according to claim 1 , wherein a range of an AF area is an outline of the AF area.

6. An auto-focus system comprising:

a picture-taking lens device detachably attached to a camera via a mount;

a first processing unit on the picture-taking lens device for controlling a focus lens and obtaining a focus evaluation value;

an AF processing section for obtaining, said focus evaluation value;

an AF area operating section for changing a range of an AF area; and

a second processing unit on the camera for sending a request to said first processing unit to send AF area display information, for displaying said AF area information on a view finder, wherein said view finder superimposes picture signals and said AF area information,

wherein said first processing unit on the picture-taking lens device performs a test to determine if said second processing unit has requested AF area display information from said first processing unit, and

if said second processing unit on the camera has requested that said first processing unit send AF area display information to said second processing unit, then said first processing unit determines that a camera associated with said second processing unit has a function of displaying said AF area information on said view finder, and

if said second processing unit has not requested that said first processing unit send said AF area display information to said second processing unit, then said first processing unit determines that said camera has no function for displaying said AF area information on said view finder.

7. The auto-focus system according to claim 6 , wherein said AF processing section comprises:

a high path filter for extracting signals of high frequency component from picture signals input from said camera, and

a gate for extracting, from said signals of high frequency component, picture signals within a range corresponding to a predetermined AF area.

8. The auto-focus system according to claim 7 , wherein a range of said AF area for extracting picture signals at said gate circuit is set by AF area signals provided from said first processing unit.

9. The auto-focus system according to claim 6 , wherein an operator can change a range of an AF area by manipulating said AF area operating section when said camera has a function of displaying AF area information relating to a range of said AF area.

10. The auto-focus system according to claim 6 , wherein said AF area operating section outputs AF area indicating information indicating a range of an AF area and provides said AF indicating information to said first processing unit.

11. The auto-focus system according to claim 6 , wherein, if said camera does not request an AF area display information, setting information of an AF area is read from a memory.

12. The auto-focus system according to claim 6 , wherein a range of an AF area that can be changed by said AF area operating section is a location, size or shape of said AF area.

13. The auto-focus system according to claim 6 , wherein, when said camera has no function of displaying AF area information on said view finder, a location of said AF area is fixed to a predetermined location.