Bildprojektionsapparat mit Autofokus-System

摘要

An image projection device comprising at least one display panel (26, 27, 28), a projection lens system (C) and a focus-error detection system is described. The focus-error detection system comprises an auxiliary radiation source (50) delivering a focus measuring beam (b), an auxiliary lens (61) for capturing radiation (br) diffusely reflected by a projection screen (D), and a detection unit (60) for measuring the size of a spot (S) formed on the screen by the beam (b).