136 PRACTICAL PHOTO-MICROGRAPHY. 



the centres of negative, projecting lens and easel should all be 

 in one line. If we are to project our image upon paper as 

 bromide paper the paper is simply fixed by drawing pins to 

 E ; if our enlargement is to be on glass, E must have a rebate 

 or other contrivance to carry the glass so that it (the glass) shall 

 occupy precisely the position of the surface upon which we 

 focus our projected image. The writer has a square aperture 

 cut in E ; in this aperture he places a sheet of ground glass, so 

 that (no light entering the apartment except through the 

 negative and lens) he can arrange and focus his image with 

 perfect ease and absolute precision. A pane of non-actinic 

 glass, or a sheet of non-actinic paper, may be used to illuminate 

 the apartment which otherwise should be dark. This pane 

 should be covered while focusing is performed. In place of 

 the angled reflector F a sheet of ground glass may be used 

 parallel to the negative, and a few inches behind it ; tissue 

 paper will answer the same purpose. 



The only remarks necessary about the projection lens are that 

 it should be capable of covering at full aperture the whole of 

 the area of negative requiring enlargement. But we strongly 

 recommend the use of a lens of focal length as long as possible, 

 so that only the central rays of its " cone " are used. The 

 only real limit to this is the length of the base-board D ; and 

 the easel E may be on wheels, or on a car on the floor of the 

 apartment. This lens ought also to be a doublet lens, one of the 

 so-called " Rectilinear " or " Symmetrical " lenses used in 

 photography. If it have a sufficiently great focal length it 

 need not be stopped down at all, as we have to deal with 

 parallel surfaces, and " depth of focus " does not come into 

 requisition. 



If it is inconvenient to have an entire apartment darkened 

 for this purpose, figure 33 will suggest an alternative. 



Here we have two cameras joined in a very simple manner, 

 the small one carrying the negative from which we desire the 

 enlargement, the dark slide of the larger camera carrying the 

 sensitive material. In this arrangement we are likely to be 

 troubled by want of stretch in the large camera which will 

 entail a short focus projection lens, this again will entail 



