eliminate, the registry of scanping "tracks" on the negative. These fine
lines, caused by voids (nonexposure) and overlaps (double exposures), F
often appeared on the orthophotographs prepared with the earlier instruments, e
and were evidence that, due to mechanical limitations, the exposing aper- f
ture failed to traverse exactly contiguous areas of the negative as ad- i
jacent strips were scanned. Although these lines do not disturb the Y
position of images, their presence degrades the appearance of the product. c
As shown in figure 2,the new instrument structure is designed
to accommodate the supporting bar both for Kelsh-type stereoplotting "
projectors and for the ellipsoidal-reflector type. Because the Geological T
Survey has as abundance of both types in constant use, the diapositives i
available for a given area are likely to be compatible with one but not i
the other of these types of projectors. For this reason, the flexibility a
in the type of projector that can be used with the Orthophotoscope con-
stitutes a decided operational advantage. F
Experience has indicated that the efficiency and the product s
of scanning is enhanced when the direction of scanning conforms with the :
‘ 0
«) S
i
a
1
Y
e
a
1
t
c
a
C
C
t
t
a
C
C
t
f
t
G
C
C
f
f
V
C
K
f
1960 Orthophotoscope with Kelsh-type projeccors.
4