1 68 PROJECTION OF IMAGES OF OPAQUE OBJECTS [Cn. VII 



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10 11 12 13 14 15 



FIG. 90. DIAGRAM SHOWING OPAQUE PROJECTION. 



In both these diagrams (fig. 90-91) the same amount of light illuminates the 

 object, and the objects are of the same size, and the objectives have the 

 same aperture. 



Fig. go. Opaque projection In. L. Incident light of parallel rays imping- 

 ing upon a picture in white and black. 



Object The opaque object in black and white the size of a lantern slide. 



1-15 The beams of light illuminating the object. The light must of 

 course fall upon the surface facing the projection objective. 



R L Reflected light. From each point on the surface of the opaque object 

 the light falling upon it is reflected nearly equally throughout the entire hemi- 

 sphere. 



Ax Axial beam on the principal optic axis of the objective. 



Objective The projection objective. Its aperture is such that it receives 

 and transmits about 20 of the 180 reflected from each point. 



From the formula given in 857:1 such an objective transmits to form the 

 screen image approximately 3% of the light reflected from the opaque object. 



