24 SCIOPTICON MANUAL. 



CHAPTER III. 



THE CONSTRUCTION OF THE SCIOPTICON. 



THE PORTRAIT OBJECTIVE. This objective (Fig. 13 

 or 15) is made for the camera, and is known mostly in 

 its relations to photography. An objective, however, 

 that with large opening, will give proper direction to 

 rays from a large object to a small image in the camera, 

 will answer equally well in giving direction to rays from 

 the small picture in the Sciopticon back to life-size on 

 a screen; both object and image being in the conjugate 

 foci in either case. 



THE PLAIN LANTERN OBJECTIVE. This objective, like 

 the achromatic portrait objective (Fig. 13 or 15), has 

 the advantage of a front and a back lens, A B (Fig. 14), 

 so far apart that the tube serves as a stop for marginal 

 rays with comparatively small loss of light. The front 

 lens A is a meniscus of crown-glass, whose tube slides 

 into a larger tube which holds the plano-convex crown- 

 glass lens B. Arranged as in the diagram, the effect 

 is scarcely inferior, so far as common observation goes, 

 to that of the most expensive combinations. With the 

 front tube reversed, so as to bring A near to B, the 

 image is larger but less distinct. With only one lens the 

 image is smaller. These different arrangements give 

 the three powers commonly attributed to lenses mounted 

 in this form. 



NO LOSS OF LIGHT FROM USING AN OBJECTIVE OF 

 LOW POWER WITH A CONCENTRATED LIGHT. 



Were the picture p (Fig. 14) made luminous by light 

 shining upon it, as in an opaque lantern, the light would 

 radiate in all directions, and in accordance with the law 



