OUTLINE OF PHOTOGRAPHY 7 



Printing. — The final operation is that of making the print by enlarging or contact 

 printing. Like the negative, the exposed print must be developed, fixed, and washed. 



Motion-picture Photogra'phy. — The differences between still- and motion-picture 

 photography are differences of degree rather than differences of fundamental opera- 

 tion. The same fundamentals are necessary, viz., illumination, lens, camera, sensitive 

 material, and chemical operations of developing, fixing, and printing. One difference is 

 that the individual pictures made are very small compared to those usually employed 

 in still photography. But many miniature cameras make negatives which are onlj^ 

 slightly larger than motion-picture frames. The chief difference between still- and 

 motion-picture photography is that in motion-picture work numerous frames are 

 exposed one after the other in rapid succession. One common practice is to make 

 24 exposures per second. 



The prints, which are made on transparent film instead of on paper are viewed 

 by projection upon a screen. When these frames are pi-operly projected upon a screen 

 in rapid succession the photographed subject appears to be in motion. Because of 

 the physiological factor known as the persistance of vision, the human eye does not 

 perceive each individual frame separately as such and is unaware that the motion 

 picture is made up of many discrete frames, none of which record any appreciable 

 motion. The film is projected intermittently, and flicker, due to the stop-start 

 motion of the film through the projection camera, must be overcome. This is accom- 

 plished by projecting a fairly large number of frames per second (usually 24) and by 

 projecting each frame twice by momentarily cutting off the light in the middle of the 

 period for which an individual frame is in the light beam. 



Amateur motion-pictures cameras employ 16- or 8-mm. film; professional machines 

 use 35-mm. film. Some 8-mm. pictures are made by using 16-mm. film which is 

 capable of recording two images side by side if the film is properly run through the 

 camera twice. In processing this film the two halves are slit apart and the ends 

 joined. 



Photography in Colors. — In color photography, a subject is photographed, in 

 effect, three times, each negative produced being made by exposure through a filter 

 which passes approximately one-third of the visible spectrum. If positive prints 

 from these three negatives are properly dyed or otherwise colored and are placed in 

 superposition, a colored image will result. This print will closely resemble the original 

 subject in form, contrast, and in color. 



Red, green, and blue-violet filters are used to divide the visible spectrum into 

 three parts for making the three negatives. The negative taken with the red filter 

 contains densities which are proportional to the amount of red present in the original 

 subject and which are passed by the red filter. Wavelengths corresponding to blue- 

 violet and green are not passed by the red filter but are passed on to the negatives 

 exposed behind the blue-violet and green filters, respectively. The process of making 

 negatives from light corresponding to only a portion of the visible spectrum is known 

 as "separation," and the negatives are known as separation negatives. It is quite 

 likely that four or more divisions of the spectrum could be made with the possibility 

 of greater fidelity in color of the final result, but this has not been found to be necessary. 



At the present time there are two general methods of color photography, the 

 additive and the subtractive methods. Both of them are based on the fundamental 

 necessity of making color-separation negatives. 



In the additive-color process the separation negatives may be made as outlined 

 above. Black-and-white prints made from these negatives on transparent material 

 (films or plates) may be placed in three projection lanterns and projected upon a 

 screen, each image being accurately registered with the others. The positive print 

 made from the red-filter negative is projected through the red filter; the positive made 



