| 摘要 |
PURPOSE:To detect a displacement by using an image forming lens for forming an image of a very small spot light to an object to be measured, and a sensor for outputting a signal corresponding to a light quantity distribution centroid position of focal shift image by the very small spot light, and outputting a displacement signal from a focusing surface of the object to be measured. CONSTITUTION:When an object to be measured is displaced in the Z direction from a focusing surface and conforms with a displacement surface of P1 or P2, a condensing point of an image of a very small spot light becomes Q1 or Q2. In this case, an image limited by an annular mask 24 of a focal shift image of the very small spot light is formed in a sensor 26. Accordingly, the sensor 26 outputs a signal corresponding to a light quantity distribution centroid position in the radial direction centering around an optical axis of this focal shift image, and a displacement signal (d) is outputted from a displacement Z of the object to be measured and a differential amplifier. Accordingly, since this displacement signal (d) is zero, it is detected that the displacement surface is a focusing surface. |
