deposition of an aluminum coating becomes the reflecting
condensing system of 120° aperture specified above.
The Mapping Projector
As an integrated member of
the Balplex family of mapping
projectors the new 120° addi
tion (Figure 4) makes use of
the same size diapositive
2
images on 110 x 110mm glass
plates, the same printer and
reduction ratio. The resulting
principal distance of this pro
jector is 31.80mm. Glass
plates of J" thickness are
preferred for their higher
stability and surface flatness,
ventional plateholders, centered therein on a standard
centering device and, when inserted in the projector,
occupy an unambigious position by which the correct re
lation to the projection lens (interior orientation)
is rigorously established. The projection lens is
mounted in a ball socket. Its center coincides with the
rear nodal point. It can be universally canted from
its initial position. It produces imagery of critical
focus at a nominal projection distance of 400mm in a
plane which is either normal upon or oblique to the axis
of projection, depending upon the controlled magnitude
of lens cant introduced to establish a depth zone
commensurate with the degree of obliquity of the aerial
photograph. The accepted depth zone is -18% of the
nominal projection distance or -70mm.
Figure 4
They are held in con-