CH. X] PHOTOGRAPHIC ENLARGEMENTS 379 



meters (14 in.) in diameter. Of course, if only a part of the nega- 

 tive plate contains the picture to be enlarged then a smaller con- 

 denser in the given case will answer. The above figures are for 

 the diagonal of the respective sizes. These condensers are usually 

 of relatively long focus, especially those of the larger diameters, 

 e. g., the 35 cm. lens ordinarily has a focus of 50 centimeters. The 

 condensers most used for enlarging are usually of the double form, 

 the convexities facing each other as for the magic lantern condenser 

 (%. 185). 



534. Objectives to use for printing. It is necessary to use 

 an objective which has been corrected for photography. The 

 ordinary projection objective gives a good visual image, but not a 

 good photographic image, hence it is better to use a photographic 

 objective. 



535. In focusing, some white paper should be put into the 

 printing frame or pinned in place and the image focused with care. 

 The photographic paper when put in the same place will then give 

 a sharp picture. 



536. Photographic paper for printing with projection appara- 

 tus. If one has sunlight or the arc light the developing papers like 

 Velox, Cyco, etc., are plenty rapid enough. If a weak light is all 

 that is available, then Haloid or one of the more rapid bromide 

 papers will be called for. 



537. Holding the paper while printing. (A) If the pictures 

 are of microscopic objects or other pictures of relatively small size 

 (i. e., up to 30 x 35 cm.; 12 x 14 in.), a good method is to put a 

 clear glass in a printing frame and press the printing paper down 

 upon it just as one does for printing from a glass negative by con- 

 tact. This holds the paper perfectly flat and ensures uniform 

 sharpness. With the printing frame one can lay it flat if a mirror 

 or prism is used, or it can stand on edge facing the objective if no 

 mirror is used. 



(B) If the printing paper is large the usual method is to have a 

 board screen on a track. The picture is then got of the desired 

 size by varying the distance between the board and the objective, 



