METHOD AND APPARATUS FOR AUTOMATIC FOCUSING OF AUTOMATIC HARDNESS METER

PROBLEM TO BE SOLVED: To enhance the percentage of success of automatic focusing even if the periphery of a dent is contaminated by calculating the difference between the position of a sample stage becoming max. in the brightness change ratio of an image and a position becoming min. in a brightness max. value to compare the same with a threshold. SOLUTION: A sample stage 14 falls to the lowermost end of stage driving height by a start command 24. When a CCD camera 20 records photographing image data at that height, the stage 14 moves upwardly by one step to record image data by the CCD camera. When the stage 14 reaches the uppermost end, an automatic focus mechanism part 26 operates the stage drive height 1 max. in the brigthtness change rate of the dent boundary part of an image and detects the stage drive height 2 becoming min. in a brightness max. value of each stage to calculate the difference between the heights 1, 2. When this difference is less than or more than a threshold, operation is repeated and, when the difference becomes the threshold or less within the fixed number N of times, the height 1 is set to stage driving height 3. When the difference does not become the threshold or less, the average value of the heights 1, 2 calculated at the N-th time is set to the height 3.