i6o CHESTER K. WENTWORTH 



wishes a picture which is one-half natural size. In Table II oppo- 

 site the ratio 2 is given the object-distance 15 inches. Then in 

 Table I, interpolating between 14 inches and 15 inches, we find that 

 the focus should be at the scale-reading of 10.85 a-nd that auxihary 

 lens II should be used. The kodak is then set with the lens 15 

 inches from the object to be photographed. Table II gives also at 

 the bottom the foci of the three combinations, the focus of the kodak 

 lens alone being about 6.75 inches. 



Fig. 2. — Photograph of bed of kodak showmg attached metric scale and two 

 tables as described in the text. (Somewhat reduced.) 



The celluloid scale may, if desired, be so set as to read inches of 

 focus from the ground glass directly; that shown was set arbitrarily 

 and the readings indicate position only. With this device, sharp 

 and undistorted photographs up to natural size may be taken by 

 using a tripod or one of the numerous types of clamp support, and 

 an aperture of F/32 or smaller. Since in pictures of this kind where 

 the object is not plane, it is almost always necessary to reduce the 

 aperture and give a time exposure in order to get depth of focus, 

 there is no additional difficulty due to the auxihary lens. Instan- 

 taneous pictures at full aperture may be made if need be, but the 



