140 



PRACTICAL PHOTO-MICKOGEAPHY. 



must at least equal the diagonal of the plate or portion of plate 

 we mean to enlarge. Thus the ordinary four-inch condenser 

 of the optical lantern is not of sufficient size to enlarge an 

 entire quarter-plate. Moreover, the larger the condenser the 

 more light it will collect, so that the exposure required, coster is 

 paribus, varies inversely as the area of the condenser. 



In practice the light is placed as nearly as possible in the 

 focus of the condenser, the negative and the condenser remain 

 fixed in relation to each other, the lens for projection is racked 

 backwards and forwards till the image is seen sharp on a trans- 

 lucent or opaque surface placed to receive the image, this sur- 

 face being parallel to the original undergoing enlargement. 

 The easel may run on a track, or may be on castors, we figure 

 a most convenient form of arrangement made by the Eastman 

 Company. 



FIG. 35. 



This easel may very aptly be used for daylight enlarging by 

 our first-described process. 



