. The book of photography; practical, theoretical and applied. nshould be about three-quarters of an half-plate cut through lengthwaj^s willprovide a suitable shape and size. This bi-chromated plate is exposed with the glassside against the graduated deposit for asuitable length of time to be ascertained as small as possible, then cut some quar-ter-plates with a diamond to a convenientsize and place one in a quarter-platecarrier with a piece of cardboard on eitherside to hold it in position. Now, bymeans of a cap made as in Fig. 596, thegraduated colour screen is arranged so asto pass i
. The book of photography; practical, theoretical and applied. nshould be about three-quarters of an half-plate cut through lengthwaj^s willprovide a suitable shape and size. This bi-chromated plate is exposed with the glassside against the graduated deposit for asuitable length of time to be ascertained as small as possible, then cut some quar-ter-plates with a diamond to a convenientsize and place one in a quarter-platecarrier with a piece of cardboard on eitherside to hold it in position. Now, bymeans of a cap made as in Fig. 596, thegraduated colour screen is arranged so asto pass in front of the diaphragm of asingle lens. An exposure is first of allmade of correct length in the ordinaryway ; next an exposure is given with thelightest tint in front of the lens, allowinga sufficiently increased time, as far asmay be judged, substituting, of course,a fresh piece of plate. Another sectionis pushed forward, a third piece insertedin the slide and a third exposure made,and so on until all the tints have beenused. Each plate must be carefully. Fig. .595.—Cap Attachment for Filter Experiments. by the actinometer. The plate is thenwashed in hot water to dissolve away thegelatine to the extent to which it may besoluble in the different portions. Whenthis preparation is complete, the plate, onbeing held up to the light, will show variousthicknesses of film which may be detectedby the vaiying densities of the whitedeposits still left in it. The plate maynow be immersed in a clean solution ofhypo, and carefully washed; it is thenbathed in a solution of aurantia until thethinnest deposit but one just shows a per-ceptible yellow tinge. A scale of colourdeposits roughly prepared in this waywill do much towards making clear theinfluence which the depth of the screenhas upon the rendering of contrast in theresult. Experiments with Graduated Screen. To use the graduated screen, proceed asfollows: Focus the image of tlie subject marked with a number, showing the tintthroug
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectphotography, bookyear
