136 . HANDBOOK OF PHOTOGRAPHY 



Negative papers are occasionally mentioned as being more economical than film. 

 The grain of the paper, however, makes them unsuited for the regular photographic 

 uses requiring contact printing or enlarging. Negative papers, or fast emulsions 

 coated on paper base, are finding wide use in various types of recording instruments 

 and for copying documents and drawings. A special waterproof paper base, coated 

 with a thin emulsion suitable for reversal processing is used for the "direct positives" 

 produced by the while-you-wait automatic portrait machines. 



Standard Sizes. — In the course of the evolution of photography, cameras taking 

 many and various sizes of films or plates have been introduced. While many of the 

 odd sizes have become more or less obsolete, enough cameras remain in use to require 

 the supplying of an unnecessarily large number of film and plate sizes. Thus one 

 manufacturer lists 30 sizes of roll films, 13 sizes of film packs, 49 sizes of cut films, and 

 37 sizes of plates. Even this does not show the total number of negative sizes, since 

 there are a number of cameras using one of the regular roll films but making an odd 

 size negative in order to get more pictures per spool. 



Fortunately, there seems to be a tendency for most new apparatus to use one of the 

 more popular sizes listed in Table V. This is very desirable since the odd sizes are 

 sometimes difficult to obtain, while the popular sizes are generally available and the 

 rapid turnover insures reasonably fresh stock. 



In connection with these sizes, it should be noted that the nominal dimensions for 

 cut films and plates are the upper limit of the actual dimensions and the lower limit for 

 interior dimensions of the film and plateholders. With roll films and film packs on 

 the other hand, the listed sizes are the nominal sizes of the picture area and the actual 

 film size may be somewhat greater. 



In commercial photofinishing it is the usual practice to employ printing masks 

 somewhat smaller than the actual negative image size in order to allow a slight toler- 

 ance in positioning the negative on the printer. 



In the case of motion-picture films the permissible variations are much smaller 

 than with cut films or roll films. The various measurements and tolerances for the 

 sizes which have been standardized in this country are shown in Fig. 10. 



The 35-mm. film is standard for professional motion pictures. Most of the prints 

 in this size are made on nitrate-base film, and in most localities there are strict safety 

 regulations governing the showing of such prints. Prints on acetate film are not 

 affected by such restrictions. 



The 16-mm. film was originally introduced as an amateur film, though it is coming 

 into more general use in educational, advertising, and other semiprofessional fields as 

 well as in strictly amateur work. Films in this size are required by law to be on acetate 

 "safety" base, which offers no more fire hazard than an equivalent weight of news- 



