1. Field of the Invention
This invention relates to a device for detecting the position of an image of an object, and more particularly to an image plane deviation amount detecting device of an automatic focusing apparatus in a camera.
2. Description of the Prior Art
A focus detecting device disclosed in U.S. Pat. No. 4,185,191 or U.S. Pat. No. 4,264,810 for making a first image and a second image by an imaging lens from light beams passed through two areas of the exit pupil of a picture-taking lens and detecting front focus, rear focus or in-focus from the amount of displacement of the first and second images relative to a pair of image position detecting photoelectric converters disposed in or near the focal plane of the imaging lens (hereinafter referred to as the amount of lateral deviation between the object images) is known in the prior art.
In a so-called automatic focusing apparatus for automatically rendering the picture-taking optical system into in-focus condition by the information of focus condition obtained from the focus detecting device of this type, the control of movement of the picture-taking lens as hereinafter described has heretofore been effected. By the information of front focus or rear focus from the focus detecting device, movement of the picture-taking lens toward the in-focus point is started. The focus detecting device detects the focus condition also during the movement of the picture-taking lens and stops the picture-taking lens when it detects the in-focus condition or the vicinity thereof.
What has been described above can be regarded as the so-called feedback loop control using an optical system. However, where there is a response delay in the focus detecting device due to the charge accumulating time or the signal processing time when a light-receiving element such as CCD is used, if the picture-taking lens is moved at the usual speed of lens movement, there is the possibility that a situation arises in which the focus detecting operation cannot overtake the movement of the picture-taking lens. In such a case, there arises the so-called hunting in which the picture-taking lens goes past the in-focus point and is again moved back in the reverse direction and therefore, the lens movement must be done at a low speed and this may lead to the problem that the automatic focusing operation cannot be accomplished quickly.