PROJECTION SYSTEM FOR AUTOMATIC FOCUS DETECTION

摘要

PURPOSE:To expand a range finding distance and to simplify the whole device by properly arranging respective elements of a projection system having a pattern image with a constant pattern on a part of a light pre-emitting part of a stroboscope. CONSTITUTION:A two-focus optical member 1 has a transparent lens part A on its center part and a lens part B for cutting visual light and transmitting infrared rays having refractive power different from that of the lens part A on the peripheral part of the lens part A. A chart 2 is arranged in the front of a light emitting tube 3 to emit the tube 3 when an object is dark or has low contrast to project the pattern image of the chart 2 illuminated by light beams in a visual area and an infrared area from the tube 3 in the object direction by the lens part A of the member 1 having a prescribed refractive power. Thus, the focus of the photographing lens can be detected by detecting only visual light through an infrared ray cutting filter. On the other hand, the light pre-emitting part for the strobe projects visual light and infrared light to the object side through the lens part A and projects infrared rays through the lens part B to find out the optimum quantity of light emission of a main light emitting part.