Three-Dimensional Photography - Principles of Stereoscopy

88 THREE-DIMENSIONAL PHOTOGRAPHY

to stereoscopic principles, both must be the same size, the hori-

zontal edges must exactly coincide, and the corresponding edges

must be regarded as homologous points in the stereogram. It will

be found that when the trimming has been completed, the left

unit picture contains more of the right side of the subject than

does the right unit picture.

It must also be remembered that good stereoscopes are so made

that the field is fully masked, so the effect of trimming for the

window effect is lost anyway. The same thing applies to the dic-

tum that only black card mounts shall be used. In a good stereo-

Fig. 5-12. The Window (0). The window is just back of the flower,

but in front of the background. This is perhaps the most effective

position for this particular subject.

Fig. 5-13. The Window (E). The window is in the foreplane of the
background. This is also very eflective and might be preferred to D
by some technicians.