) z = ??? ( p0 + p45 + p90 + p135 ) / 4 ??? ( 3 ) It should be noted that the storage unit 54 is used for storing software including a program for finding the directional sharpness magnitudes d0 (f), d45 (f), d90 (f) and d135 (f) described above, a program for finding their center positions p0, p45, p90 and p135 from the directional sharpness magnitudes d0 (f), d45 (f), d90 (f) and d135 (f) respe