398 OUTDOOR RECREATION 



interior must be painted black, and absolutely light tight-. 

 By following these directions you can make a good camera. 



Cut a hole one half inch in diameter in the middle of one side or end 

 of the box. On the inside of the box paste over the hole a piece of tinfoil. 

 In this tinfoil you will make your pinhole. The success of your picture 

 depends on the care with which you make this hole. The best results are 

 obtained when the diameter of the pinhole is in proportion to the square 

 root of the distance from the pinhole to the plate. 1 Paste cardboard strips 

 on the inside of cover to hold the sensitized plate. 



The exposure, depending on the light, should be from 

 ten to twenty minutes. The picture is made on a glass 

 plate which is held in place by narrow strips of cardboard 

 glued in along the vertical edges of the plate. This plate 

 is to be put into the camera while in a dark room. Of 

 course, the pinhole should be kept covered until you reach 

 the object you wish to photograph and covered again after 

 the picture is taken. 



Camera lenses and their use. There are two types 

 of lenses used, a single lens, found in most cheap cameras, 

 and a lens tube with a double combination of glasses in 

 it which may be of long focus. There is also a wide angle 

 lens of short focus, which is excellent for working indoors. 

 We also have the telephoto lens, which is used for long 

 distance work, and is excellent for photographing birds, 

 and other forms of wild life. 



1 Use the following formula : 



Diameter of pinhole =K^ Distance of plate from pinhole 

 K= .0008 



This diameter may be measured by some machinist or science instructor who has a microm- 

 eter caliper, who can measure a needle of the right diameter, so you can make the hole just 

 the size of the needle. 



Having obtained a needle of the right diameter, do not force it all at once into the tinfoil, 

 but work it slowly, putting pressure first on the one side, and then on the other so as not to 

 stretch the foil when pushing the needle into the hole. When you have made the hole, be 

 sure to smooth off the edges, as a clear picture cannot be made unless you have a clean cut 



