The present invention relates to an automatic focus control device having a plurality of focus detecting regions.
Conventionally, an automatic focus detecting device having a single focus detecting region, in which a defocus amount is corrected in accordance with assembly errors of an optical system, has been proposed in, for example, Japanese Patent Laid-Open Publication No. 126517/1984. However, an automatic focus detecting device having a plurality of focus detecting regions, in which a defocus amount is corrected for each of the focus detecting regions, is not known.
As shown in FIG. 7, in the case where automatic focus detection is performed in three focus detecting regions, i.e. a horizontally elongated focus detecting area A disposed at a center of a photographing field S and a pair of vertically elongated focus detecting regions B and C disposed at opposite sides of the photographing field S, CCD light-receiving element arrays e1, e2 and e3 corresponding to the focus detection regions A, B and C, respectively are provided on one chip as shown in FIG. 4. If only one CCD light-receiving element array, for example, only the CCD light-receiving element array corresponding to the central focus detecting region A is provided, positional adjustment of the CCD chip in the direction of its optical axis can be performed by performing positional adjustment of only the central portion of the CCD chip in the direction of the optical axis. However, in the case where a plurality of, for example, three CCD light-receiving element arrays are provided as described above, parallelism of the CCD chip plays an important role. Namely, when parallelism of the CCD chip is poor, deviation in the direction of the optical axis occurs at opposite sides of the CCD chip. When parallelism of the CCD chip is poor, deviation in the direction of the optical axis occurs at opposite sides of the CCD chip. Even in the case of only one CCD light-receiving element array, the deviation also takes place at opposite sides of the CCD chip but assumes a small value. Meanwhile, also in the case where a plurality of the CCD light-receiving element arrays corresponding to the focus detecting regions, respectively are not provided on a single chip, deviations of the assembled CCD light-receiving element arrays in the direction of the optical axis are different from each other, so that it becomes necessary to correct the respective focus detecting regions in the direction of the optical axis.
As shown in FIG. 6a, a focus detecting device has been widely used in which an image formed by a light-receiving lens a is re-formed by a pair of reimaging lenses d1 into first and second images on a light.TM.receiving element array el arranged in a straight line and a distance between the first and second images is detected by the light-receiving element array el such that a focusing state is detected. In this known focus detecting device, when the, distance between the first and second images assumes a predetermined value, a decision of an in-focus state in which the image is formed on a predetermined focal plane is made. Meanwhile, when the distance between the first and second images is smaller and larger than the predetermined value, decisions of front and rear focus states in which the image is formed forwardly and rearwardly of the predetermined focal plane are made, respectively such that deviation amounts of the distance between the images from that of the in-focus position are outputted as defocus amounts. At the time of focus detection, the distance j between the first and second images is obtained and the defocus amount .DELTA..epsilon. is calculated by multiplying the distance j by a predetermined coefficient s. The above described Japanese Patent Laid-Open Publication proposes correction of the coefficient s since the coefficient s for the front focus state is different from that for the rear focus state.
In the CCD chip of FIG. 4, it is considered that if a length of the CCD light-receiving element arrays e1 and e3 corresponding to the focus detecting regions B and C disposed at opposite sides of the photographing field, respectively is made smaller than that of the CCD light-receiving element array e2 corresponding to the focus detecting region A disposed at the center of the photographing field, a focus detecting module can be made smaller in size by a difference between the length of the CCD light-receiving element arrays e1 and e3 and that of the CCD light-receiving element array e2 and a time period required for effecting data dump from the CCD light-receiving element arrays el and e3 can be reduced. To this end, as shown in FIG. 4, a pair of reimaging lenses d1 and a pair of reimaging lenses d3, which are, respectively, disposed at opposite sides of the CCD chip, have distances Dd1 and Dd3 smaller than a distance Dd2 between a pair of reimaging lenses d2 disposed at a center of the CCD chip, so that the numbers of the elements required for the CCD light-receiving element arrays e1 and e3 are determined accordingly. However, in this case, such a problem arises due to the difference between the distances Dd1 and Dd3 and the distance Dd2 that a coefficient for converting a distance between the first and second images into a defocus amount on the CCD light-receiving element array e2 is different from a coefficient for converting a distance between the first and second images into a defocus amount on the CCD light-receiving element array e1 and a coefficient for converting a distance between the first and second images into a defocus amount on the light-receiving element array e3.
In FIG. 6a, the distance De1 between the first and second images on the light-receiving element array e1 changes according to changes of a distance Dd1 of the reimaging lenses d1. Therefore, in the case where the reimaging lenses d1 are made of, for example, plastic, the distance Dd1 of the reimaging lenses d1 varies in response to temperature change, so that the distance De1 between the first and second images on the light-receiving element array e1 changes, thereby resulting in also change of the defocus amount. Thus, Japanese Patent Laid-Open Publication No. 235110/1985 discloses that temperature of the focus detecting device is detected such that the defocus amount is corrected in accordance with the detected temperature of the focus detecting device.
Meanwhile, if temperature rise occurs in the case where as shown in FIG. 4, a pair of the reimaging lenses d1 and a pair of the reimaging lenses d3, which are, respectively, disposed at opposite sides of the CCD chip, have the distances Dd1 and Dd3 smaller than a distance Dd2 of a pair of the reimaging lenses d2 disposed at a center of the CCD chip, so that the numbers of the elements required for the CCD light-receiving element arrays e1 and e3 are determined accordingly, amounts of change of the distances between the two images on the CCD light-receiving element arrays e1, e2 and e3 upon temperature rise are different from each other due to the differences among the distances Dd1, Dd2 and Dd3 even if the reimaging lenses d1, d2 and d3 are made of an identical material. Meanwhile, in the case where the reimaging lenses are not made of an identical material, the reimaging lenses have different coefficients of thermal expansion, so that amounts of change of the distances between the images on the CCD light-receiving element arrays e1, e2 and e3 upon temperature rise are different from each other for the respective focus detecting regions.