206 PHOTO-MICROGRAPHY. [CH. VIII. 



minishes the labor of the artist about one-half it increases that of the 

 preparator ; and herein lies one of its chief merits. The photographs 

 being exact images of the preparations, the tendency will be to make 

 them with greater care and delicacy, and the result will be less imagi- 

 nation and more reality in published scientific figures ; and the objects 

 prepared with such care will be preserved for future reference." 



" In the use of photography for figures several considerations arise : 

 i°. The avoidance of distortion ; 2°. The adjustment of the camera to 

 obtain an image of the desired size ; 3 . Focusing ; 4 . Lighting and 

 centering the object ; 5 . Obtaining outlines for tracing upon the 

 drawing-paper." 



" i°. While the camera delineates rapidly, the image is liable to dis- 

 tortion. I believe opticians are agreed, that, in order to obtain correct 

 photographic images, the objective must be properly made, and the 

 plane of the object must be parallel to the plane of the ground glass. 

 Furthermore, as most of the objects in natural history have not plane 

 surfaces, but are situated in several planes at different levels, the whole 

 object may be made distinct by using in the objective a diaphragm with 

 a small opening." 



" 2 . By placing the camera on a long table, and a scale of some kind 

 against the wall, the exact position of the ground glass for various 

 sizes may be determined once for all. These positions are noted in 

 some way (on the brass guide, 3, in the apparatus here figured). 



Whenever it is desired to photograph an object, natural size, for ex- 

 ample, the ground glass is fixed in the proper position indicated on the 

 brass guide (Fig. 162, 3). Then as the relative position of the objec- 

 tive and the ground glass must not be varied, it is necessary, in focus- 

 ing, to move the camera toward or away from the object, or the re- 

 verse. To do this, the camera is fastened to a board which moves in a 

 frame by means of a screw Fig. 162, 7. Whenever the camera is to be 

 moved considerably, — as to a position for twice natural size from one 

 giving an image of half natural size, — the position of the camera on 

 the board is changed by loosening the two thumb-screws clamping it to 

 the movable board (Fig. 162, 5, 6). The approximate position for the 

 various sizes being once determined and noted, it is but a moment's 

 work to set the camera for any enlargement or reduction within its 

 range." 



3 . The object is placed on a horizontal support, and so arranged 

 that the lighting will give prominence to the parts to be especially 

 emphasized. For a contrasting background, black velveteen for light, 

 and white paper for dark, objects, have been found excellent. 



