434 HANDBOOK OF PHOTOGRAPHY 



the ease of supplying sufficient light to print in a reasonable time. In this case, 

 however, care must be taken to dissipate the heat effectivel}-. 



Use of Camera as Enlarger. — If a camera has a removable back and if it has suffi- 

 cient bellows extension to accommodate the range of magnification desired, it may be 

 made into a successful enlarger. All that is necessary, in addition to the camera, 

 for the negative to be enlarged is a source of even ilhimination and a holder. 

 The light source may be made up of several low- wattage bulbs in a white wooden box, 

 or a metal box painted with glossy white paint, of such dimensions that it fits over the 

 rear of the camera. One or more plates of opal or ground glass may be interposed 

 between the bulbs and the rear of the camera to secure even illumination. These 

 diffusion mediums should be a short distance from the film to be enlarged so that the 

 grain of the diffusion medium is not in focus at the same adjustment that brings 

 the negative image into focus on the easel. Reflectors of any sort placed back of the 

 bulbs will improve the light efficienc3^ 



The film or plateholder may be simply two glass plates between which the negative 

 is placed. Masks may be fixed, permanently, to the glass plates. A simple slot 

 structure into which the assembly of glass plates and negative fits will enable the nega- 

 tive to be held parallel to the rear of the camera during focusing and exposure. 



These homemade enlargers are usually horizontal, although it is not impossible 

 to make a vertical system that is entirely satisfactory. The photographic journals 

 have published many descriptions of such equipment. Several such articles are 

 noted below. 1 



With four 40-watt bulbs and a single sheet of opal glass, exposures of the order of 

 10 sec. to several minutes may be required when enlarging 9- by 12-cm. negatives up 

 to 8 by 10 in. with a 13.5 cm., //4.5 lens. 



One of the problems with homemade enlargers is to maintain the negative and 

 the easel parallel to each other and perpendicular to a line through the center of the 

 camera. Another problem is to get even illumination over the entire negative. If the 

 negative is small, this is not so difficult, but in this case considerable degrees of mag- 

 nification may be required, and then the proper mounting of camera, negative, and 

 easel becomes different. 



It is probably uneconomical to attempt the construction of a high-grade miniature 

 enlarger at home. The precision of construction must be considerable if high-class 

 enlargements are to be made. 



Exposure Related to Magnification. — With diffusion enlargers the exposvire required 

 for any desired degree of enlargement when the correct exposure is known for some 

 other degree of magnification is given by 



„ (il/2 + 1)^ X E, 



^■' == (ili, + 1)^ ^^^ 



where E\ and Mi correspond to the known exposure time and magnification and il/2 

 and E2 are for another degree of magnification. 



To Measure Degree of Enlargement. — If two lines are scratched on a plate which has 

 been thoroughly fogged and processed, the ratio of the distance between the lines 

 projected on the easel to the actual distance on the negative will be a measure of the 

 degree of enlargement. Th^is, if the lines are cm. apart on the final print and only 

 1 cm. apart on the negative, the image has been enlarged five times. 



1 HiBBS, Wyatt, a Horizontal Enlarging Outfit, Am. Phot., July, 1935. This used four photofloods 

 with a switch to reduce the voltage by a series connection for focusing. The camera' was an Zeiss Ideal 

 B. 



Ramley, Edward J., A Reflected Light Source, for Photographic Enlarger, Am. Phot., September, 

 1937. 



Jardine, Donald C, A Home-made Vertical Projection Printer, Camera, February, 1936. 



