| 摘要 |
PURPOSE:To utilize light effectively and hold the illuminance on a screen the same or more even with less electric power by using a secondary curved surface reflecting mirror and an annular prism and allowing light emitted from a light source in a circumferential direction to contribute to projection. CONSTITUTION:Light emitted forward from the light source 11 is made incident to the center part 16a of a Fresnel lens 16 through a condenser 13 and light emitted backward is reflected by a spherical reflecting mirror 12 and incident to the Fresnel lens 16 through the condenser 13 as well as the light emitted forward. Further, light emitted from the light source 11 in a circumferential direction is reflected by an approximately parabolic reflecting mirror 14 and refracted by the annular prism 15 to enter the circumferential part 16b of the Fresnel lens 16. Thus, the light in the circumferential direction which does not contribute to projection conventionally at all contributes to the projection and this light has a large value almost a half as large as that of the whole luminous flux emitted from the light source 11, so a projection image on the screen 19 is 1.5-2 times as bright as before. |
