This method is, on account of its inconveniences and difficulties, only used when it cannot be possibly avoided.
Fig. 5.
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Fig. 5 shows the arrangement in which the prism a is placed in front of the lens b. The prism is three-cornered and the angle turned to the objective is a right angle. The hypothenuse is silvered. It is mounted in brass or nickel; on the mount is a screw, by means of which it is fastened to the objective, so that the side opposite to the hypothenuse lies upright to the side of the camera, and this position must be an exact right angle to the focussing screen. The camera itself must be absolutely horizontal. The subject to be taken, instead of being in front of the camera, is placed sideways to the prism. The image passes through a′, falls on the silvered hypothenuse a″, from there through the objective b, through the box-shaped extension c and the camera d, on to the sensitive plate, which is not visible in the diagram. The exposure with the prism is about 1/5th longer than usual, because a portion of the light is absorbed by the prism.
(B.) PLACING THE PLATE THE WRONG WAY ROUND IN THE SLIDE.
Generally, for making reversed negatives of line drawings, it is quite sufficient to place the sensitive plate the wrong way round in the dark slide or in the carrier, so that the film side, instead of being towards the objective, is turned towards the operator. It is, of course, absolutely essential to use only glass plates which are absolutely clean and which contain no particles of sand, air bubbles, etc., which would show on the prepared negative as points. After sensitizing the plate, the back of it must be thoroughly cleaned, for any smudges or drops would be visible on the negative. Obviously great care should be taken also in cleaning the plate to make as little dust as possible. In the Imperial and State Printing Works nearly all the reversed negatives are prepared most satisfactorily in this way.
The photographic manipulations, the preparation, sensitizing and developing of the plates, etc., is exactly the same as with direct negatives.
(C.) STRIPPING NEGATIVES.
There are various directions for making stripping negatives.