| 摘要 |
PROBLEM TO BE SOLVED: To provide a contactless extensometer capable of sufficiently improving the detection accuracy always clearly picking up the image of a reference line marke on a test piece independently of a change of thickness of the test piece. SOLUTION: A device is provided with cameras 1, 2 for picking up the image of a reference line mark on a test piece S, and provided with a focal point adjusting mechanism 24 for automatically adjusting the focal point of the cameras 1, 2. Displacement of the focal point is detected (focal point displacement detecting unit 23) on the basis of the high frequency component of the image signal picked up by the cameras 1, 2, and focal point of a image pickup lens system 21 is adjusted on the basis of the detected information. Image pickup magnification is corrected on the basis of the adjusted focal point position (image pickup magnification correcting unit 25). |
