1 88 PROJECTION OF IMAGES OF OPAQUE OBJECTS [Cn. VII 



direct a parallel beam, a converging or a diverging beam (see also 

 Ch. XIII-XIV on radiants and lighting). 



If a condenser is used, its size must be adapted to the size of the 

 object, that is, the diameter of the cylinder of light must be some- 



FIG. 105. DIAGRAM SHOWING THE OPTICAL PARTS AND THE COURSE OF 

 THE RAYS IN THE CONVERTIBLE BALOPTICON IN OPAQUE PROJECTION. 



(Cut loaned by the Bausch & Lomb Optical Co.). 



The lamp-house, radiant and first element of the condenser are so inclined 

 upward that the light from the condenser falls directly upon the opaque object. 



A Upper carbon of the arc lamp furnishing the light. 



B First element of the condenser to render the diverging light parallel. 

 The lens beyond the meniscus is double-convex instead of plano-convex as in 

 fig. 3- 



D Position of the opaque object. Objects as large as 20 x 20 cm. (8x8 

 inches) can be illuminated and projected. 



E Large aperture projection objective in a vertical position. 



F Mirror beyond the objective to reflect the image to the screen and correct 

 the inversion. 



C Mirror. It serves to increase the illumination of the opaque object by 

 reflecting back upon it some of the scattered light. 



6" Second element of the condenser for lantern-slide projection (fig. 3). 



// Projection objective for lantern slides. 



Bellows. 



M Lathe bed on which slide the objective, etc. 



