144 



HOW WE USE LIGHT 



pinhole in the front end of a small box. Brightly lighted 



objects in front of the pinhole send light through it and 



an image is formed at the 

 back of the box. If a film 

 coated with chemicals 

 sensitive to light is there 

 to receive the image, the 

 start of a photograph is 

 made. The advantage of 

 having a lens instead of 

 the pinhole is that it pro- 

 duces a sharp image when 

 the opening is large, thus 

 permitting more light to 

 enter. This shortens the 

 time of exposure. With 

 a pinhole camera any 

 opening larger than a 

 small pinhole l will make 



a blurred image. With a hole small enough to give a 



good sharp image, it will take from 10 to 20 minutes to 



make the exposure. 



The Diaphragm and 



Shutter. The lens camera 



has a diaphragm, the ad- 

 justment of which makes 



possible different sizes of 



opening through which 



light may enter. There 



is a shutter controlled to 



allow an exposure of a 



fraction of a second for a 



"snap shot" exposure or 



r , Can you tell the use of each of the parts 



for a time exposure when O f the camera named in the diagram ? 



1 See page 162 for directions. 



Eastman Kodak Co. 



The camera used by amateur photogra- 

 phers. 



lens 



