CAMERAS AND PICTURE-MAKING 315 



Be sure the diaphragm is closed. Insert the plate holder at 

 the back of the camera and make certain it clicks into place, 

 the ridge upon it settling into the slot provided so as to exclude 

 the light. Draw the slide that covers the plate straight out. 

 If it is tilted so that one corner is withdrawn before the other, light 

 may leak in at the corner first withdrawn because the other 

 corner prevents the little clip, operated by a spring, from closing 

 along its entire length. Now make the exposure by pressing the 

 release or bulb. In some cameras the release that opens and 

 closes the shutter must be lifted to set the spring that operates 

 it before it will work. Attend to this, if necessary, before making 

 the exposure. Return the slide that covers the plate in the 

 same careful way it was withdrawn. 



The operation will be the same for film cameras, except that 

 one judges the distance of the object and sets the pointer on 

 the scale accordingly. In roll film cameras there is no slide 

 over the film to withdraw. In reflecting cameras like the Graflex 

 and Reflex, the image is thrown by a mirror on to a ground 

 glass, the mirror serving to protect the film or plate from the 

 light. One sees the image of the object up to the moment the 

 trigger is pressed that swings the mirror out of the way and 

 immediately releases the shutter to make the exposure (Fig. 160). 



The plate or film must be taken out of the camera (except 

 in those provided with daylight-loading devices), and developed 

 in the darkroom. The glass plate or film used in the camera 

 has one face covered with a thin layer of gelatine so treated that 

 it does not dissolve readily ; in this film there are imbedded mi- 

 nute particles of certain silver salts, usually the bromide and iodide 

 Wherever light strikes this film, the silver salts are so affected 

 that, in developing, the metallic silver is deposited in tiny grains, 

 giving the area a black appearance. If you will take a plate out 

 of its box in the darkroom, you will see that one side of it is shiny, 

 the other dull. The shiny side is the uncovered glass, the dull 

 side that upon which the gelatine is spread. Cover one-half 

 of such a plate with a piece of cardboard, then bring the plate, 



