(506) 
The camera obtains optical images in all types of linear perspective from 
the positioning of the restricting aperture of the system, and not necessarily by 
changing the distance of the terrain model from the camera window. In order 
to explain the optical principle of aperture-entrance pupil conjugate relation 
and the camera’s perspective control, a laboratory experiment devised by Prof. 
Robert W. Pohl and illustrated in his “Introduction to Optics” (Einführung In 
Die Optik) as figures. 121 to 124 was 
displayed on the wall along with a simi- 
lar demonstration with three simple con- 
denser lenses. 
The model on display represented 
the terrain around Bear Mountain and 
West Point on the Hudson River. It was 
constructed on a Transverse Mercator 
graticule at a scale of 1:25,000 which 
was uniform for both the relief and the 
model datum. A uniform square grid was 
inscribed on the surface and on the bor- 
ders of the relief model: the borders of 
the model were in the same plane as the 
river surface. In many respects this ter- 
rain model is typical of the rapidly grow- 
ing relief mold library at the Army Map 
Service except that the majority of library 
mold copies at the AMS are at 1:250,000 
horizontal scale. At present, the main use 
of this library is for the forming of the 
plastic copies of the plastic relief maps 
being produced for military purposes. 
In Fig. 2 is shown a portion of the 
approach toward the south in parallel 
oblique projection. The relief or vertical 
dimension is exaggerated optically three 
times over the horizontal dimensions of 
the model. For descriptive reasons the 
vertical dimension of the terrain model 
was called the z axis of the relief and the 
Fig. 2. Parallel Oblique Perspective model’s horizontal dimensions as repres 
(3 : 1 Vertical Exageration). sented across and up the picture at right 
angles to one another, the horizontal x 
and y axes respectively. This type of perspective allows the photogrammetrist 
to exaggerate the z axis any amount desired. 
The parallel oblique view represents the easiest of the oblique photo- 
projections to make on the Bench Camera and lends itself most readily to scal- 
ing. The negative is made by placing the model on the easel board on the tele- 
centric or collimated side of the camera — the photographic plate i is placed on 
the conical side of the system. After development, the negative is then projected 
from the conical side with a special care to replace che negative in the exact 
position at the camera back in which it was originally exposed. When aligning 
  
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