DO AND DO NOT IN OPAQUE PROJECTION tCn. VII 



297. Summary of Chapter VII: 



Do 



1. Select an objective of large 

 aperture for opaque projection 



( 275)- 



2. Use a light of great brill- 

 iance like sunlight or the arc 

 light ( 274, 277). 



3. Make the screen image 

 only six to ten times as large as 

 the object ( 287). 



4. Make the projection room 

 very dark ( 280). 



5 . Use a very white screen or 

 under some conditions a metal- 

 lic screen ( 286, 621). 



6. From 25 to 50 amperes of 

 direct current are needed to 

 give good opaque projection 



( 289). 



7. If lantern slides and 

 opaque objects are projected at 

 the same exhibition, use a 

 neutral tint (smoky) glass to 

 make the lantern-slide image as 

 dim as the image of the opaque 

 object ( 282). 



8. Use a condenser for opaque 

 objects somewhat larger than 

 the object (see fig. 114). 



Do NOT 



1. Do not undertake opaque 

 projection with an objective of 

 small aperture. 



2. Do not expect good 

 opaque projection unless from 

 20 to 50 amperes of direct cur- 

 rent, or greater amperages of 

 alternating current are avail- 

 able. 



3. Do not try to magnify the 

 object too much. 



4. Do not try to project in a 

 light room. It must be dark. 



5. Do not be satisfied with a 

 dirty, non-reflecting screen. It 

 must be white. 



6. Do not expect brilliant 

 screen images with a weak light. 



7. Do not pass quickly from 

 the dim pictures of opaque 

 objects to the brilliant pictures 

 of transparencies. Dim the 

 transparencies down to the 

 opaque images. 



8. Do not use a small con- 

 denser for a large object. 



