SCIENCE-GOSSIP. 



163 



THE PHOTOGRAPHY OF COLOUR. 



By E. Sangee Shepherd. 



i Concluded from pagi 112.) 



WE have considered the theoretical conditions 

 necessary for securing a record of the 

 colours of a natural object. Let us see how we 

 may best carry our knowledge into practice. 



First, with regard to the most convenient appa- 

 ratus for taking the negatives. We may mount 

 our three coloured light filters in little brass caps, 

 so that they may be easily slipped over the front 



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Fig. 13. Photography of Colour. 



of the hood of the lens, and place our plates in 

 three dark slides in the ordinary way, but changing 

 the dark slides and light filters between the suc- 

 cessive exposures takes up time, and there is the 

 liability of shifting the camera during the opera- 

 tion. A very little experience in making tri- 

 chromatic negatives in this manner will quickly 

 convince the photographer of the inconvenience of 

 so many operations, and the early investigators 

 soon turned their attention to what was at that 

 time a very popular piece of apparatus with the 

 portrait photographer — the ,; Eepeating Back." 

 By mounting a frame at the back of the camera, 

 furnished with a dark slide long enough to take 

 three plates' side by side, the plate may be easily 

 changed by sliding the plate-holder along to stops. 

 Such an apparatus is represented in fig. 13 attached 

 to an ordinary quarter-plate camera, and fig. 14 

 represents the separate parts. The back proper, A, 

 is fitted to the camera by means of a panel cut to 

 match and interchangeable with the dark slide, so 

 that the attachment can be taken on or off in a 

 few seconds ; in this back slides a frame B, in 

 -which the blue-light filter c, the green-light filter 

 D, and the red-light filter E are mounted. At the 

 top and bottom of the frame are brass plates, which 

 serve to hold the double dark slide F, which takes 

 one long plate 8" x 3 \", so that the dark slide and 

 the colour filter can be changed together by one 

 movement. There are three depressions in the 

 side of the colour-filter frame B, into which the 



pin of the spring latch 11 drops when the filters 

 are central with the opening in the back, .\. 



Such a piece of apparatus is very compact and 

 will enable the photographer to obtain perfect 

 negatives of a very large variety of subjects, 

 landscapes, portraits, still life, etc. ; and as it can 

 be attached to any piece of apparatus that will 

 project a sharp image upon the plate, it is per- 

 fectly satisfactory for photo-micrography, polari- 

 scopic and spectroscopic work. The apparatus 

 occupies only a space of 14|" x 5" x 1^", and forms 

 but a small addition to the landscape photo- 

 grapher's outfit. For special purposes there are 

 many other forms of camera available. For in- 

 stance, where a large number of colour photo- 

 graphs are required from fiat surfaces, paintings, 

 coloured book illustrations, maps. etc.. a camera 

 may be used furnished with three rectilinear lenses, 

 when all three exposures can be made simul- 

 taneously, the work being quite as easy as ordinary 



Fig. 14. Photograph* of Colour. 



photography. Such a form of camera cannot, how- 

 ever, be used for ordinary work from objects in 

 relief, as the points of view of the lenses are 

 separated, and the prints from the three negatives 

 when superposed would not register correctly. In 

 order to take three negatives of such objects simul- 

 taneously, a more complicated camera, furnished 

 with one lens and a set of reflectors behind it. 



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