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XT. 



ON PHOTOGEAPIIY BY REFLECTION UNDER CONTACT. 

 By E. E. FOURNIER d'ALBE, B.Sc, A.R.O.Sc, M.R.I.A. 



[Published May 10, 1909.] 



(Plate VIII.) 



In the usual methods of contact photography, a copy is taken of the original 

 or negative by allowing light to pass througli tlie latter on to a sensitive 

 surface. The resulting picture is due to diSereaees in opacity in the 

 various points of tlie original or negative. 



Tlie new method to be described consists in transmitting tlie liglit in the 

 reverse direction, and producing a picture, not by differences of opacity, but 

 by differences of reflecting power in tlie original.' 



The obvious objection to such a metliod is that the sensitive film, being 

 exposed to a uniform incident illumination coming through the back of the 

 plato, will be uniformly "fogged"; and the resulting positive will lie marred 

 by a brightness wliicli invades and partly obliterates all the dark portions. 

 If this difificulty can be overcome, we obtain a method of copying any flat 

 picture or design without a camera ; and we avoid the difficulties of distortion, 

 curvature of field, chromatic and spherical aberration, flare, astigmatism, and 

 lack of uniformity of illumination, which beset all but the best lenses, and 

 which cannot, in practice, be simultaneously reduced to a negligible amount. 



When the original to be copied has no half-tones, it is possible, by 

 suitable exposure and development, to eliminate the fog entirely. The 

 general principle is to employ exposures and developers which in ordinary 

 photography "suppress the detail in the shadows," or, in other words, confine 

 the developed image to those portions which have received the maximum 

 illumination. In copying a line-drawing, a page of print, or similar fuU- 



' Such a reflection process was devised in 1897 by J. H. Player (see "The Photographic 

 Journal," 1897, p. 222). He used bromide paper, and transmitted the light through a green 

 glass. He " could not succeed with plates." It is said (ibid.) that positive copies of maps were 

 for some time made in the French army by contact with Ilford process plates, but no details are 

 given. — E. E. F. 



