Cameron County press. [volume] (Emporium, Cameron County, Pa.) 1866-1922, 1898-03-10
THE CAMERA IN SURVEYS.
Most important Use for Photography
That Has Been Yet Devised.

That Has Been Yet Devised.
Something like $4,000 square miles of
the mountainous country of western
Canada has been surveyed with the
camera. Nothing comparable to this
in the way of Photographic surveying
has been accomplished on any such
scale anywhere else in the world.
The causes of failure on the part of
many who have tried the method and
discarded it in disgust are chiefly two.
One of these is a defective knowledge
in descriptive geometry and perspec-
tive, which are essentials of the plot
ting of Photographic surveying. The
other difficulty lies in the manipulation
of the Photographic apparatus itself
and the making of a proper negative.
This is by no means the easy thing it
seems, since photographs that would
be highly acceptable to the average
photographer, professional or amateur.
might be useless for the purpose of the
surveyor. For example, the surveyors
picture, in order to be of use, must
be taken with the camera in precise
ly the horizontal position, fitting never
a hairs breadth in one direction or
another; the lens he uses must be an
anastigmat, and absolutely ,rectilinear
that the image may not be in the least
distorted; and the plate must be of a
special kind, and adjusted in the cam
era with a degree of nicely of which
the ordinary photographer has no con
ccption.
Mr.. Deville, who had in charge the
Canadian work, points out in Il prac-
tical way how many of the worst diff
ficultics may be easily overcome. Thus
the simple device of having net sus-
pended between the legs of the tripod,
in which stones are placed to steady
the camera, would save many rega-
tive in windy weather that now is lost
through the vibration of the instru-
mcnt. And the care which is counseled
in determining the exact period of
proper exposure for a given plate, lens
and light, even if carried out with far
less scientific precision than is here
suggested, would enable many an anna
tour who now wastes several plates for
every good negative to reverse the pro-
portions of failure and successes.
One curious feature of the photo
graphic surveying, which the amateur
would not care to follow ordinarily,
but a knowledge of which might prove
of service on occasion, is that the aerial
perspective, making the distance hazy,
is practically eliminated by the use of
orthochromatic plates, which are little
affected by the blue rays, combined
with the use of an orangc-colored
screen in front of the lens. The result,
of course, is a picture devoid of at
mosphere, and hence defective from
the artistic standpoint, but probably
more valuable for the purposes of the
surveyor, who very likely has taken the
picture solely to show the exact loca-
ton, altitude and contour of IL distant
mountain.
'Shc use of these methods of restrict
irS t,ie light necessitates very long eX-
pose. e, and this in turn makes requisite
th.- use of plates coated on the back
vita Notwithstanding material (so-
called nonhalation plates), else the
!!gnt reflected from the back surface
Ct the plate would fog the film. Mr..
Deville is careful to point out that this
coating must be in optical contact with
ehe surface of the glass; in other words,
actually painted upon it, the mere plac-
ing of n black cloth or paper against
the back of the plate being of no serv-
ice whatever.
When all these technical difficulties
of Photographic surveying are made
clear, it no longer seems so str;-e ge
that the method has been but slowly
adopted by surveyors. even in those
districts where its advantages would be
most marked The surveyors who tried
it usually failed to get any available
results, and they did not realize that
the fault lay with themselves and not
with the method.-N. Y. Sun.