| 摘要 |
PURPOSE:To decrease malfunction due to change in an objective, by providing a circuit generating a fluctuation detecting signal with more fidelity with a simple constitution only when the object is changed. CONSTITUTION:A video signal from a camera is obtained from a terminal 3, it passes through a low pass filter 19 and is amplified at an amplifier circuit 20. A signal waveform obtained at a terminal 171 is the result that the signal is passed through the filter 19 having sufficiently low cut-off frequency in comparison with the cut-off frequency of an equivalent low pass filter characteristic of a lens when the lens is placed at out of focus, then even if the lens is placed at a point with maximum out of focus from the focusing point, the change in the waveform is less. Further, when the object is changed, the frequency spectrum of the pattern changes from a low to a high frequency component, the level fluctuation of the waveform is detected at a fluctuation detection circuit 18. |
