| 摘要 |
PURPOSE:To reduce contrast blur by dividing a spot circle with a boundary line which extends to above and below the lateral center line of the spot circle so that the upper and lower divided shapes are equal in area and do not project from the spot circle. CONSTITUTION:The boundary line which extends to above and below the lateral center line X-X of the spot circle consists of upper and lower boundary lines 5-1 and 5-2 parallel to the lateral center line X-X and a perpendicular 5-3 running in the center of the spot circle, dividing the spot circle into upper and lower sensors 5A and 5B to the same area. When a spot image of an object having contrast is formed on the sensors, spot light based upon a high reflection factor R strikes on even the sensor 5B after the spot center O shifts by (q) and its output increases abruptly, so that both outputs becomes equal eventually. Thus, contrast blur is eliminated.
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