The product is composed of three base,two biconvex lens,one biconcave lens, three supporting rod, white screen, ground glass, frosted glass screen in, light source, and so on. Base material for engineering plastics, bottom diameter:80mm, height:35mm; Lens diameter 40mm, substrate using optical glass production,One of the biconvex focal length is 100±3mm，another is 50±3mm, the biconcave lens focal length is -75±5mm,The operating voltage of the light source is DC 1.5 ~ 3V.