PRINTING PROCESSES 437 



negative represents and opacity of 4, and that the densest portion an opacity of 40. 

 The ratio of these two quantities is 10. The printing paper, therefore, must be 

 capable of reproducing an exposure range of 10 to 1 to reproduce accurately the 

 opacity ratio in the negative which, it is assumed, accurately reproduces the brightness 

 range of the original subject. 



Many other schemes have been developed for measuring the transmission of light 

 through a film in an endeavor to determine the opacity ratio or the density difference 

 over the desired portions of the negative scale. These may employ various forms of 

 comparison photometers; or they may permit direct measurement of the quantity of 

 light transmitted through the film. In the simplest case, a source of light distinct 

 from the enlarger illumination is varied, by an iris diaphragm in the lens, until the 

 illumination on the easel through the negative just matches the illumination on the 

 easel from the external source as determined from visual examination. Then by trial 

 and error the exposure necessary to produce a good print on a certain grade of a certain 

 kind of paper is determined. Once determined, this exposure will be the same under 

 the same conditions. All that is necessary is to have sufficient adjustment of the 

 illumination through the objective to cover all types of negatives that will be printed. 

 The eye is surprisingly accurate in making illumination comparisons of this 

 kind.i 



A simple and inexpensive device of recent development is an adaptation of the 

 well-known grease-spot photometer. A small battery-operated incandescent lamp 

 illuminates one side of a semitransparent piece of material. The image from the 

 enlarger is focused upon this screen, and the lamp current is adjusted by a rheostat 

 until the screen illumination from the lamp and from the focused image have the same 

 brightness as viewed by the photographer. The rheostat is calibrated in terms of 

 exposure and contrast grades of modern papers. 



Prints for Half-tone Engravings. — In the Agfa Diamond, for January and February, 

 1938, Lloyd Varden, speaking of prints for reproduction, states: 



"In decreasing order of preference we might list print surfaces for reproduction 

 purposes as follows: 



"1. Black and white prints of uniform glossy or semiglossy surface. 



"2. Semi-matte or smooth matte white surfaces. 



"3. Rough or textured surfaces." 



Now it is quite true, that among half-tone workers a preference is made for either 

 glossy, ferrotyped or unferrotyped, or smooth semimatte papers. Glossy prints, 

 especially on paste-up jobs, create undesirable reflections, and for this reason are not 

 so satisfactory for this work as semimatte surfaces. Especially contrasty negatives 

 are best printed on semimatte or smooth matte surfaces, for the final reproduction is 

 enhanced by the softening of contrast due to the matte paper. However, if a negative 

 is of normal contrast, or of flat contrast, it is best printed on glossy paper, and for the 

 latter instances, therefore, glossy surfaces cannot be surpassed. Art work, if neces- 

 sary, usually calls for a surface other than glossy, but print retouching is by no means 

 impossible on glossy prints. Under all circumstances, time permitting, the engraver 

 should be consulted about the proper surface, for he might have very excellent sugges- 

 tions to offer, and the photographer also has an opportunity to explain his reason for 

 wanting to use a particular paper. 



1 The following bibliography will direct the reader to several sources of data on homemade pho- 

 tometers, etc., for this purpose. Especially, the reader should consult "Perfect Print Control," by 

 Lawrence Dutton, Galleon, 1937. 



Colt, Ralph S., Simple Method of Timing Enlargements, Am. Phot., April, 19.38. 



Brockman, Frank G., Photoelectric Timing for Projection Printing, Am. Phot., September, 1936. 

 Sec also discussion of this paper by Ronald L. Ives, Am. Phot., September, 1937. 



Weiland, W. F., E.xposure in Projection Printing, Am. Phot., July, 1936. 



