| 摘要 |
PURPOSE:To adjust simply and surely the focus of a cathode ray tube, by placing a photodetector in front of a projecting lens, and adjusting the focus of the cathode ray tube to make the output of the detector lowest. CONSTITUTION:A lens system 2 is provided in front of a fluorescent part 100 of a cathode ray tube 1 constituting a projector, PIN photo diode 4, light detector, is placed at the center of a lens cover provided in front of the lens system 2. Output signal Dout corresponding to the brightness of the fluorescent face 100 is detected by this diode 4, and the signal Dout is supplied to a peak hold circuit 6. The maximum level emitted at the center of the fluorescent face 100 is held by the circuit 6, and reset by a synchronizing signal VD from a terminal 6a at each vertical period. The output SPH of the circuit 6 is added to an active LPF7 and a DC output is added to a display meter 8. The focus is adjusted to make the signal Dout lowest by output of the meter 8. |
