PRINTING PROCESSES 429 



Fixed-focus Enlarger. — If the photographer is content with a single degree of 

 enlargement, he may use a fixed-focus enlarger. The maximum size of film that may 

 be enlarged is controlled by the dimensions of the negative holder; the size of the 

 largest sheet of paper upon which the image may be focused is controlled by the dimen- 

 sions of the paper holder. Ordinarily these enlargers are used by amateurs who are 

 accustomed to use a single size of negative and who are satisfied with a single size of 

 paper, e.g., 3}'^ by 4}^ in. enlarged to post-card size or to 5 by 7 in. The lens is placed 

 at the proper position between the negative and the paper and is sufficiently corrected 

 for the purpose. After the negative and printing paper have been placed in their 

 respective holders, the enlarger may be brought out of the darkroom and exposure may 

 take place to the open sky or to some other source of illumination. The camera may 

 be knockdown in style so that it may be packed out of the way when not in use or so 

 that it may be readily transported ; more modern fixed-focus enlargers contain a source 

 of illumination. 



Variable-focus Enlargers. — This type of equipment is much more versatile than tht; 

 fixed-focus arrangement. With such an enlarger, any degree of magnification between 

 the minimum and maximum possible with the phj'sical equipment may be accom- 

 plished. In addition, if the lens may be placed far enough away from the negative and 

 close enough to the easel, a print reduced in size from the negative may be secured. 



Variable-focus enlargers may fall into one of two general classes depending upon the 

 type of illumination. If a single source of light (usually a concentrated filament lamp 

 or an arc) is used, a pair of plano-convex condensing lenses is employed to bring the 

 light to a focus in the center of the objective (focusing) lens. This type of equipment 

 is more economical of light, and it requires more adjustments than the type described 

 below in which diffused lighting is used. Flaws and negative grain become more 

 apparent in prints made from this type of equipment than is the case when using the 

 second type. 



The second general type of equipment utilizes one or more lamps, the illumination 

 being broken up by diffusion plates (usually ground glass or opal glass) interposed 

 between source and negative so that the difi'using medium becomes the source of light 

 as far as the enlarging process is concerned. A diffusion system provides even illiuni- 

 nation over the entire negative without any adjustments of lamp-to-negative distance; 

 flaws and grain are minimized but much of the available light is wasted in the diffusion 

 equipment. Prints made from diffusion-type enlarger will be less contrasty than those 

 made from a condenser system. 



Some enlargers, notably those used for enlarging miniature negatives, use a con- 

 denser lens to concentrate the beam and a diffuser to provide even illumination. 



Present trends are toward the diffusion type of equipment. 



In any variable-focus enlarger there are two adjustments necessary to get sharp 

 focus of the image upon the printing paper: the lens-to-negative distance and the 

 lens-to-paper distance. In addition to these adjustments a condenser sj^stem requires 

 that the light-source-to-negative distance be accurately adjusted to get even illumina- 

 tion over the entire negative. 



In operation the photographer places the negative in the holder and focuses the 

 image to the required size upon the easel by adjusting the distances mentioned above. 

 Then he may stop down the objective lens to the desired point, place the projection 

 paper on the easel, and make the exposure. Proper exposure is controlled both by the 

 diaphragm in the lens and by the time of exposure. Stopping down will tend to 

 minimize effects of poor focusing, but it is always wise to effect the best possible focus 

 before making the exposure. 



If the light source requires adjustment, this is done after the desired magnification 

 has been determined and before the negative is placed in the holder. The distance, 

 light to negative holder, is varied until the easel is evenly covered with illumination. 



