FOCUS DETECTION DEVICE AND METHOD

A focus detection device includes a pair of photoelectric converting element arrays that output a pair of signal strings and a focus detection optical system, including a photo lens, that conducts a pair of light rays from a subject to the pair of photoelectric converting element arrays. A filter extracts a pair of signal strings having a predetermined frequency component from the pair of signal strings outputted by the photoelectric converting element arrays. A calculation range setting device sets a calculation range of signals of the pair of extracted signal strings, and a focus detection calculating device calculates a focus adjustment condition for the photo lens based on the signals of the pair of extracted signal strings in the calculation range. A contrast calculation device calculates the contrasts in areas outside the calculation range based on the signals of the pair of extracted signal strings excluded from the calculation range, wherein the operation of the focus detection calculating device is dependent upon the calculated contrasts. When the calculated contrast exceeds a predetermined value, focus detection calculations based on a pair of signal strings with lower frequency components are not carried out, or else the shift range for correlation calculations is narrowed, or else the threshold values for reliability determination are changed and the reliability determination standard is made to be more restrictive, or else the focus detection calculation range is narrowed.