CAMERA 



1080 



CAMERA 



which has layers of different colors, with the 

 figures so engraved that they appear in one 

 color and the background in another. Onyx, 

 sardonyx and agate are the stones in gen- 

 eral use for cameos, but very beautiful arti- 

 ficial specimens are produced from various 

 kinds of shells and fine glass. Shell in partic- 

 ular yields cameos of rare delicacy and loveli- 

 ness. A famous specimen of an imitation of 

 cameo in glass is the Barberini Vase in the 

 British Museum, made at Rome about the first 

 century before Christ. This has a blue back- 

 ground and figures of a delicate, half-transpar- 

 ent white. Both the Greeks and the Romans 

 excelled in the art of cameo cutting. At the 

 present time dinner rings with cameo settings 

 are highly popular. See PRECIOUS STONES. 



CAMERA, kam'era, the popular name for 

 any apparatus used for taking pictures by 

 photography. The term is really the Latin 

 word for chamber, and is abbreviated from 

 camera obscura (which see). The camera ob- 

 scura works ex- 

 actly like the hu- 

 man eye. In the 

 eye the crystal- 

 line lens reflects 

 upon the sensi- 

 tive retina any 

 rays of light com- 

 ing from the out- 

 side; in the cam- 

 era obscura the 

 rays are reflected 

 upon a screen, 

 placed in a dark- 

 ened chamber, 



just as the retina THE FAMILIAR "KODAK" 

 is in a darkened chamber of the eye. In the 

 ordinary photographic camera the place of the 

 screen or retina is taken by a sensitized cellu- 

 loid film or glass plate. The film or plate is 

 previously prepared so that it will preserve 

 the image of any objects reflected on it. 



There are as many different kinds of cameras 

 as there are purposes and personal tastes. The 

 essential parts, however, are few and are easily 

 remembered the box, the lens, the shutter and 

 the screen. The box is fitted with a telescopic 

 arrangement, made of light-proof cloth, rubber 

 or other material, by which the lens can be 

 placed at a proper distance from the screen 

 (see LENS). At the outer end of this telescope 

 arrangement is a frame in which the lens is 

 set; at the other end, at the back of the box, 

 is the screen. In large cameras, such as those 



used by professional photographers for taking 

 portraits, a piece of ground glass, in a frame, 

 is used as a screen. The photographer moves 

 the lens backward and forward until the image 

 on the screen is clear. Then he is ready to 

 remove the screen and substitute the sensitized 

 plate. He covers the lens with a cap, which 

 usually contains a shutter. The speed with 

 which the shutter opens and closes can be 

 regulated to a fraction of a second, and the 

 size of the opening is also adjustable. The 

 period during which the shutter is open is 

 called the exposure, for the sensitized plate is 

 exposed to the rays of light, which pass through 

 the lens. A large camera is usually mounted 

 on a tripod when in use, to keep it motionless 

 during the exposure. 



The smaller, or hand, cameras are exactly the 

 same in principle, though slightly different in 

 details of manufacture and operation. Large 

 cameras, with glass plates, are not easily car- 

 ried around. The first notable improvement 

 was the substitution of sheets of celluloid film 

 for glass. The sheets were separated by black 

 paper, and when a film was exposed it was 

 withdrawn from the camera together with its 

 protecting black paper. The film "packs," 

 as they were called, were not entirely satis- 

 factory, and the latest cameras all use films 

 in rolls. The entire roll, mounted on a spool, 

 is inserted in the camera, and as it is exposed 

 bit by bit is 

 gradually rolled 

 up on a second 

 spool. The roll 

 of film is pro- 

 tected from the 

 light by black 

 paper. 



Small cameras 

 also differ from 

 large ones in the 

 method of ad- 

 justing the lens 

 and making 

 the exposure. 

 They have an ad- 

 ditional pair of 

 lenses, called the 

 finder. These are 

 mounted outside 

 the telescopic ar- 

 rangement and 

 have no connec- CAMERA USED BY 

 tion With the pho- PHOTOGRAPHERS 



tographic lens; they are in the same relative 



