| 摘要 |
PROBLEM TO BE SOLVED: To reduce production cost and to omit conventional focusing operation by making the depth of focus of right and left projection lenses longer than that of a central projection lens so that a swing angle may be zero. SOLUTION: The projection lens Lr is arranged in front of an R color cathode ray tube CRT-r so that its optical axis may be orthogonal to the display screen of the CRT-r. The projection lenses Lg and Lb are similarly arranged. The lenses Lr, Lg and Lb are designed to be focused on the point O of a screen S, and designed so that the depth of focus of the lens Lr +fR11 to -fR2 and the depth of focus of the lens Lb +fB1 to -fB2 may be longer than the depth of focus of the lens Lg +fG1 to -fG2. When the swing angles of the CRT-r and the CRT-b are zero, a projected picture is inclined at the position of the screen S and projected, but the depth of focus of the lenses Lr and Lb is made longer, so that out-of-focus on the periphery parts of the R and B color projected pictures is inconspicuous.
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