| 摘要 |
PURPOSE:To perform focus detection while the adverse influence of a fluorescent lamp is eliminated completely by selecting respective band-pass filter (BPF) outputs in order at a specific period. CONSTITUTION:A video signal is amplified by a preamplifier 14 and sent to the process circuit of a video camera, but applied to BPFs 16, 18 and 20 for focus detection as well. The BPF 16 is for the intermediate frequency band, the BPF 18 is for the high frequency band, and the BPF 20 is for the ultra high frequency band. A switch 46 selects one of the BPFs 16, 18 and 20 selectively and periodically according to a switching signal from a filter switching signal generating circuit 56. The filter switching signal generating circuit 56 is a combinational logic circuit which generates 2-bit signals 72 and 74 from the vertical synchronizing signal of a camera part and a BPF to be selected is determined according to the combination of those 2-bit signals. Consequently, a selection is made excellently and focus detection is carried out while the adverse influence of a fluorescent lamp is precluded. |
