"Floss". A. W. Lester.
Trimming may be done by the aid of glass trimming gauges, but better by means of a 5 in. trimming board with pivoted shear-blade, or a small Merrett trimming-desk. Both prints must be trimmed to exactly the same size. The width of either should not exceed 2 3/4 in.; it may be as much less as the subject or the quality of the print demands. There is no need to include a defective edge or redundant marginal detail for the sake of full width. The height may be anything within the limits of the mount, and should be determined by the character of the subject. Many prints can be cut down to 2 1/2 in., or less, with advantage.
The two prints should coincide exactly as regards their upper and lower edges. In the case of the side edges a little variation may be introduced with good effect. If the inner edge of each print, as finally mounted, includes an eighth of an inch more of the photograph than the outer edge of the other print, the effect in the stereoscope will be that the entire view will appear to lie beyond the plane of the mount. (See illustration, "Guy's Mill.") This has been called the "window effect," because the sensation is that of looking at a view through an open window, of which the mount represents the frame. This method of trimming suits most subjects, but a contrary method is sometimes admissible in the case of flowers, still life, and small objects, the foremost parts of which may thus be made to appear nearer than the plane of the mount. Effective use has been made of this "dodge" in our second stereograph, "Floss." On viewing this stereoscopically, the dog appears to be standing with his head partly through the circular opening. It is a method which should only be used with great moderation, an exaggerated effect being anything but pleasing. The difference in the trimming, by either method, should be measured by the nearest foreground object.
The standard size of stereoscopic mounts is 7 x 3 1/2 in. The most suitable colour is chocolate brown; light-tinted mounts should be avoided. Dry mounting with adhesive tissue is best; if a paste mountant is used it should be one containing the minimum of moisture. Clean, smooth mounting is as important as good photographic technique. The prints should be so arranged on the mount that the distance from a point in the foreground of one to the corresponding point in the foreground of the other is not less than 2 1/2 in. or more than 2 7/8 in.
Fig. 64. Primus Stereoscopic Transparency Printing Frame.
For vivid realism and pure photographic beauty, nothing can compare with a good stereoscopic transparency. Given a suitable negative, it is quite easily made, either by contact printing or by copying in the camera. There are three methods of contact printing:
(1) From the uncut negative in an ordinary printing frame, afterwards trimming the sides with a glazier's diamond, transposing, and mounting on a plain glass. This is not a method to be recommended, as the transparency has to be cut into four pieces, making the binding up a matter of some difficulty.
(2) By first cutting, transposing, and trimming the negative, and exposing in an ordinary printing frame.
(3) By the use of a transposing frame, which obviates the necessity of cutting either negative or transparency. Such a frame is shown in Fig. 64. It is a little more than half as long again as the negative, which is first placed as shown in the figure. The transparency plate is then placed with its left-hand half (film downwards) in contact with the right-hand half of the negative (film upwards). The frame is closed and an exposure made, through an aperture 2 3/4 in. wide on the side of the frame not shown in the figure. The relative positions of negative and plate are then reversed, a second exposure made, and the plate developed and fixed.
Undoubtedly the best method of transparency-making is by copying in the camera. The taking camera may be used for the purpose, provided it has ample extension and adjustable lens separation. The other apparatus required is simply a flat board fitted at one end with an open box having a central vertical partition as shown in Fig. 65. In the outer end of this box (not seen in the figure) is an aperture, to accommodate the negative in such a position that its central division coincides with the partition of the box. The camera should slide between guides fixed to the baseboard, to ensure parallelism between negative and focussing screen.
The negative having been placed in its aperture, upside down and film-side out, the image on the focussing screen may be examined like an actual stereoscopic slide, with a hand stereoscope, and the separation of the lenses of the camera adjusted so that the right amount of subject is shown on each side. The exposure is made on a transparency plate, in the same way as when enlarging in a daylight enlarging camera. The space between camera and negative-box should be covered with an opaque cloth to shut off extraneous light. In making transparencies by this method there is no trouble of transposition, as the lenses re-invert the images, thus correcting the original inversion.
As in the case of paper prints, a warm tone suits most subjects best, and transparency plates which give warm tones by development are to be preferred, for this reason. The rules given in connection with the trimming and mounting of prints, as regards dimensions and separation between corresponding points, should be closely observed in transparency-making. The transparency is finished by masking and binding up with a cover-glass, similarly to a lantern slide, except that the mask is a double one. Ready-made stereoscopic masks can be obtained, but it is better to cut the mask to suit the subject, or build it up of binding-strips. With a transparency made by contact, the cover-glass forms the front; with one made in the camera as above described, it forms the back. Some stereographers back their transparencies with ground glass, but this is neither necessary nor desirable, as all stereoscopes designed for the viewing of transparencies are fitted with ground glass diffusers, and the grain of the ground surface is less obtrusive to the eye, if transparency and diffuser are separated a little, than if bound up in contact.