68 THREE-DIMENSIONAL PHOTOGRAPHY
key plate, it may be easily followed. Here we see the elongation
in depth and the increased apparent distance caused by having the
camera lens of shorter focal length than the viewer lenses or
having viewer lenses of longer focal length than the camera lenses.
It is all the same, but at times we overlook this obvious inter-
change of terms.
When the focal length of the camera lens is greater than that
of the stereoscopic lenses, the reverse is true, Having gone through
both types of diagrams in detail, we do not believe it essential to
PnPdFig. 4-9.