DEVELOPMENT OF CONVEX AND CONCAVE LENS 



337 



This arrangement is used in enlarging cameras, moving picture 

 apparatus and stereopticons, reflectoscopes, and the object glass of 

 the compound microscope. 



FIG. 213. The rays of light spread over a road by a lens. 



If an object is placed at the principal focus of a lens, no image is 

 obtained. If the object is a light the rays of light pass out of the 

 lens in parallel beams. 



FIG. 214. 



This principle is applied in the bull's-eye lantern, the lenses for 

 automobile lamps, lighthouses, and spotlights on the stage. 



If the object is placed nearer to the lens than the principal 



