| 摘要 |
PURPOSE:To display a marker without changing the luminance of a grating pattern and the marker and to enable an observer to easily observe a grating point even if the marker is flickered by displaying the frame type marker surrounding the grating point of the grating pattern to be a convergence adjusting point. CONSTITUTION:When a marker horizontal position of a port P1 coincides with an output from a frequency dividing counter 12, a coincidence circuit 14 outputs a coincidence pulse (d). The pulse (d) outputs a signal (e) having right and left pulse width equal about a grating pattern vertical line signal (c) through a D.FF 16. The horizontal position and width of the marker are determined by the signal (e). A signal for determining the vertical position and width of the marker is obtained by counting an output signal (h) from a frequency dividing counter 13 by a counter 17 and outputting a coincidence pulse l from a coincidence circuit 15 based on coincidence between the marker vertical position of a port P2 and the output of the counter 17. An AND circuit 24 finds out AND operation between the advancing signal (h) with 14H phase and a delayed signal (j) with 14H phase based on the pulse l and a grating pattern horizontal line signal (i) to form signals (f), (g) to be the horizontal frames of the marker. Signals to be the vertical frames of the marker are formed by forming a pulse width signal (k) by a D.FF 20 and forming a marker vertical line signal by the AND circuit 24.
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