| 摘要 |
PURPOSE:To automatically correct defocus of a projection optical system by detecting the contrast of a pattern projected on a screen and driving and displacing all or part of the projecting lens in the optical axis direction so as to maximize the contrast. CONSTITUTION:A periodic projecting pattern 70 is received by a line sensor 31 arranged so as to be nearly orthogonal to a projecting pattern 70 on a screen 4 and a periodic contrast distribution is converted into an electric signal. The output of the line sensor 31 is inputted to a contrast detection circuit 32, applies sequentially to an envelope detection circuit 52 and a detection circuit 53 to be an output of the contrast detection circuit 32. Since the focus is adjusted so as to maximize the contrast, the sequence control to maximize an output voltage Vd of the contrast detection circuit is implemented. |
