Patent ID: 7502065

Claim:
A focus detection apparatus for detecting a focus state of an object image in accordance with a contrast of said object image, said focus detection apparatus comprising: a lens system through which said object image is formed, said lens system including a focusing lens group movable along an optical axis thereof within a predetermined range of movement; and a controller for detecting a contrast value of said object image at each of a plurality of different positions of said focusing lens group while moving said focusing lens group in a direction from one end to an other end of opposite ends of said range of movement; said controller being configured to establish a first predetermined number and a first critical value when at least one of a maximum contrast value and a minimum contrast value among said contrast values respectively detected at said different positions of said focusing lens group by said controller is outside of a predetermined range based on maximum and minimum contrast values, and establishes a second predetermined number, which is greater than said first predetermined number, and a second critical value, which is less strict than said first critical value, when both said maximum contrast value and said minimum contrast value are within said predetermined range; said controller being configured to compare contrast values detected at two adjacent positions of said focusing lens group with each other in said direction from said one end to said other end of said range of movement of said focusing lens group, wherein when said controller establishes said first predetermined number and said first critical value, said controller determines whether said contrast value of said object image increases once and subsequently decreases successively by a number of times equal to said first predetermined number, and when said controller establishes said second predetermined number and said second critical value, said controller determines whether said contrast value of said object image increases once and subsequently decreases successively by a number of times equal to said second predetermined number; said controller detects said maximum contrast value when said controller determines that said contrast value of said object image increases once and subsequently decreases successively by a number of times equal to one of said first predetermined number and said second predetermined number; wherein said controller determines a difference between said maximum contrast value and a contrast value detected at a position of said focusing lens group which is spaced from a position thereof at which said maximum contrast value is obtained by a distance corresponding to one of said first predetermined number and said second predetermined number in one of opposite directions spaced from said maximum contrast value; and wherein said controller selects said maximum contrast value when said difference exceeds one of said first critical value and said second critical value.