Color band removing focus adjusting method in overhead projector

Abstract

Abstract PURPOSE: To prevent the production of color bands by elevating a projecting lens perpendicularly along the axial center extension line of the center part of an eccentric Fresnel lens and moving a light source lamp on said axial center extension line along with its elevation. CONSTITUTION: In the case of matching the focus of projecting images, a projecting lens 15 is elevated in the perpendicular direction along the axial center extension line b of an eccentric Fresnel lens center part 12a while the parallel relation with a stage 11 is being maintained and is so vertically moved that the center 15a of the projecting lens 15 always passes the axial center extension line b. Next, when a light source lamp 14 is retreated down to the e position while, e.g., the projecting lens 15 is being lowered down to the d position on the axial center extension line b, the luminous flux of the projecting system condensed by the Fresnel lens 12 assumes the C state and therefore the whole of the luminous flux C passes through the projecting lens 15. Hence, on color bands are produced in the images projected onto a screen 17 and the good images are formed. In this way, the production of color bands may be prevented. COPYRIGHT: (C)1980,JPO&Japio

Inventors

• 👤 Toyoo Ishii

Bibliographic Details