| 摘要 |
PURPOSE:To read a focus accurately by picking up an image of an area to be detected to specific slit width, and making a decision on the level of the output of a photoelectric converting means and adjusting the focal length of an image- forming means so that the width of the area to be detected is maximum. CONSTITUTION:Marks are provided on an article at specific intervals and scanned by an ITV3. Its video signal S1 is converted by a register 18' into a binary signal S2, which is inputted to an FF14 through an inverter 11, FF12, and AND gate 13. An AND gate 16 inputs the signal obtained by inverting the output of the FF14 by an inverter 15 and the output of an AND gate 10 and the output S5 of the FF12 to obtain sampling pulses S7 having a period corresponding to the intervals. The output S7 is counted by a counter 17, whose output is stored in a register 18. The contents of the last screen are stored in a register 19 and both stored values are supplied to a subtracter 20 to find their difference, whose absolute value is compared with the set value of a setter 22 by a comparator 21 to determine a focus accurately at the position where the interval is maximum. |
