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PHOTOGRAPHY IN NATURAL COLOURS
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fm. de Abney and Sanger-Shepherd. In order that any such camera may be of real use for landscape work, or, indeed, for use in general work where the three-colour process is employed, it must be so arranged that the three images fall on one plate so that they may be developed simultaneously. The images on the plate must also all three be of the same size for the same objects at whatever distance from the camera these objects are situated, so that it may be possible to obtain complete register. Then, lastly, if the images are all taken at the same time on one and the same plate, there is bound to be a slight stereoscopic effect, and this must be reduced to a minimum.
It should be remembered that in this work, in which exposure is made through colour filters, longer time has to be allowed than when exposing without a filter. Thus with lens working at //8, each of the three plates, if of the rapid-colour plate type, as supplied by SangerShepherd, require an exposure of about a second if the light is good.
The plates are developed in the ordinary manner, metol being used in preference as the developer, and great care must be taken to exclude all light while developing.
Most beautiful lantern slides can be made by this process. The first step is to make a black lantern slide by using the negative obtained with the red filter. This slide is then converted into a greenish blue transparency by the action of a special solution. The positives from the green
Fig. 104.
A Camera with repeating hack is here shown.