| 摘要 |
PROBLEM TO BE SOLVED: To use them as focus error detecting light and to use one more light as excepting error detection by dividing a diffraction element to four areas with X, Y axes and respectively generating both of±1st-order diffraction light. SOLUTION: The diffraction element 3 generates±1st-order diffracted light converged on forward/backward of a light detection means 6 when a focus error detection object exists on a light converged point of an image forming means. This diffraction element 3 is divided to four areas 3a-3d by the X, Y axes, and the light diffracted by respective areas 3a, 3b, 3c, 3d form beam spots 8aa, 8ab and 8ba, 8bb and 8ca, 8cb and 8da, 8db on the light detection means 6. At this time, the beam spots 8aa, 8ba, 8ca, 8da are the beam spots formed by the + 1st-order diffracted light, and the beam spots 8ab, 8bb, 8cb, 8db become the beam spots formed by the -1st-order diffracted light. In such a manner, the matter that both or one side of respective±1st-order diffracted light are generated in four areas of the diffraction element 3 becomes possible.
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