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John Adolphus Flemer.

An elementary treatise on phototopographic methods and instruments, including a concise review of executed phototopographic surveys and of publicatins on this subject online

. (page 20 of 33)
Online LibraryJohn Adolphus FlemerAn elementary treatise on phototopographic methods and instruments, including a concise review of executed phototopographic surveys and of publicatins on this subject → online text (page 20 of 33)
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Q= handle to facilitate mounting of the camera;
KI= head of pinion to elevate or lower the camera-lens, the
slide S having .a corresponding rack for that purpose;
K 2 = differential pinion for slow motion;
H = clamp-screw to secure the slide 5 in a given position;
m (Fig. 148, Plate LXX VII )= millimeter scale to measure
the vertical change of the lens from its normal or
central position, the vernier n permitting such change
to be read to 0.05 mm.

The camera may be securely fastened to the vertical axis
of the horizontal circle by manipulating the central clamp-screw
from the interior of the camera-box.

When the instrument is in adjustment the zero mark of the
vernier n will coincide with the 70 mark of the scale m, and the



SURVEYING CAMERAS AND GEODETIC INSTRUMENTS. 247

lens will then be in its central or normal position. The slide 5
may be moved 70 mm. up or down; from 70 to 140 the lens wfll
be above the normal position.

The lens of this camera is a Zeiss anastigmat, //i8, with
a focal length of about 212 mm.

The camera -lens is suitable for phototopographic purposes
if the horizontal change in the distance between its second nodal
point and the image plane does not exceed

0.09 o.n 0.15 0.22 o . 45 mm. for distances of

500 400 300 200 100 m.

Hence, focusing may be dispensed with for general photo-
topographic purposes; still, in order that this camera, for special
purposes, may also produce sharp and well-defined pictures of
objects comparatively close to the camera, its lens has been
mounted to admit a longitudinal motion, in the direction of
the optical axis, within a range of 2 mm,, thus giving the
means to focus objects that are only 23 m. distant from the
camera.

The external tube of the lens mount has a helical groove,
or slot, in which a small metal block /, Fig. 149, Plate LXXVIII,
provided with an index mark, may travel. This block / is attached
to the inner tube of the lens mount, and a screw r, Fig. 149,
Plate LXXVIII, at one end of the slot serves to clamp the two
tubes together when the focal length is to be maintained con-
stant for any length of tune.

Loosening the screw r and revolving the outer tube from left
to right will shorten the focal length, and when the block t has
passed from one end of the slot to the other, the focal length
will have suffered a change in length of 2 mm.

The two positions of the index mark on the block t for these
extreme limits are marked on the outer side o and 2, Fig. 149,
Plate LXXVIII; the interval is divided into twenty equal parts,
one division corresponding with an axial motion of the camera-
lens of o.i mm. A metal frame is attached in the rear to the



248 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS,

camera sides and the posterior surface of this frame coincides
with the image plane. The inner edges of this metal frame
are provided with a centimeter graduation, the middle marks
of the two horizontal sides indicate the position of the principal
line, while the middle notches of the two vertical sides mark
the position of the horizon line. When the camera is adjusted
these lines will intersect each other in the principal point of the
photographic perspective. The inner opening of the metal
frame is 17.8 and 22.8 cm., which, of course, is also the size of
the pictures.

The two frames I and 77, shown in Figs. 150 and 151, Plate
LXXVIII, give the means to make a light-tight connection
between the single plate-holders (or ground glass) and the camera-
box. The short bellows W, connecting frames / and //, will
admit the frame II to be moved toward or from the frame 7,
which is securely attached to the camera-box. Each one of these
frames I and II is provided with two hooks ; frame / has an upper
hook hi, Figs. 148 and 149, Plates LXXVII and LXXVIII,
and a similar hook near the lower corner diagonally opposite hi.
The hook h 2 , Fig. 149, Plate LXXVIII, is attached to the upper
corner of frame //, opposite hook hi, and frame II has a similar
lower hook diagonally opposite h 2 and directly below hook hi.

Fig. 151, Plate LXXVIII, represents the section of a rear
corner of the camera-box, showing the ground-glass-plate attach-
ment V (it also has the eyepiece forming a telescope with the
camera-lens, Fig. 152, Plate LXXIX).

Frame // is secured to frame / by means of the upper left
hook h 2 and the lower right hook. The ground-glass frame V
is supported by the screws Z\ and Z 2 , Figs. 151 and 152, Plates
LXXVIII and LXXIX, the points of which rest upon the metal
plates TT, Figs. 149 and 151, Plate LXXVIII, permanently
attached to the fixed frame 7. The face of the ground glass G,
Fig. 151, Plate LXXVIII, is brought into contact with the rear
surface of the graduated frame R by means of the upper right
and lower left hooks.



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 249

The position of the optical axis of the eyepiece may be adjusted
vertically by turning the screws Zi and Z 2 until the line of col-
limation of the eyepiece and camera-lens coincide in the horizon
plane, the camera-lens being in its normal position, the zero
mark of vernier n coinciding with the 70 mark of the scale m,
Fig. 148, Plate LXXVII. In this position points may be observed
through the eyepiece of the ground-glass attachment. When the
camera-lens has been moved some distance up or down (away
from its normal position), however, the eyepiece can no longer
be used with its line of collimation in a horizontal position, and
the clamps, or stops, pi and p 2 , Fig. 152, Plate LXXIX, are
unfastened and the eyepiece is tilted up or down it rotates about
a horizontal axis x L x 2 , Fig. 152, Plate LXXIX until its optical
axis is directed to the center of the object-glass. The image of
the point to be bisected will then appear well denned.

The circular openings p, shown in the ground -glass attachment,
Fig. 152, Plate LXXIX, serve to examine the middle notches (of
the inner edges of the graduated metal frame R) which define the
termini of horizon and principal line of the perspective. The
openings p give the means to test the positions of those lines with
reference to the middle notches; both should coincide. The outer
wooden frame V, Fig. 151, Plate LXXVIII, of the ground-glass
attachment is strengthened by two metal diagonals D joined into
a ring at their intersection, which ring supports the eyepiece,
revolvable about Xi% 2 as axis.

Each holder contains but one plate, and Fig. 150, Plate
LXXVIII, shows a section through the upper rear part of the
camera with a plate-holder K in position.

P= dry-plate;

/= springs supporting the dry-plate at its four corners;

G= hard-rubber slide, which is completely withdrawn when a
plate is to be exposed;

R= graduated metal frame permanently secured to the rear
of the camera-box;

C = section of camera-box wall.



250 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

To attach a plate-holder K to the camera, Fig. 1 50, Plate
LXXVIII, frame 77 is set free from / and K is hung to frame //
by means of the bent plate / (permanently attached to K) when the
beveled projecting frame or edge of K closes into the corresponding
rebate of frame //, producing a light-tight connection. K is
secured to // with the upper left and lower right hooks, giving
it the position shown in Fig. 150, Plate LXXVIII. After the
hard -rubber slide G has been withdrawn, the second pair of hooks,
upper right and lower left, are tightened to draw the holder K
forward until the sensitive-film surface is brought into contact
with the graduated metal frame R (at the back of the camera), the
springs / serving as a cushion to insure a perfect contact without
straining the glass plate P. The lens is now uncapped, the
exposure made, and the holder is withdrawn by repeating the
same operations in inverse order: unfastening the pair of hooks,
upper right and lower left, inserting the slide G, and drawing back
the two last hooks, lower right and upper left.

N. Capt. von HubPs Plane-table Photogr ammeter.

This instrument, manufactured by R. Lechner in Vienna, has
been described in Lechner's " Mittheilungen aus dem Gebiete der
Photographic und Kartographie," Wilhelm Miiller, Graben 31,
Wien. It is the result of Capt. Hiibl's endeavors to reduce the
weight and costs of an effective photographic-surveying instru-
ment, to be easily adjusted and manipulated and to subserve
topographical purposes.

As the final result, generally aimed at in topography, reduces
itself to the graphical representation of the terrene, Capt. Hiibl
combined the surveying-camera with a plane table by means of
which the directions needed for the orientation of the picture
traces, as well as those required for the location of the camera
station, may be plotted directly in the field. It is supposed that
a sufficient number of triangulation points had been provided
to locate the camera stations by resecting upon signals, of which at
least three should be visible from every camera station.



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 251

For this purpose the camera top M (21X21 cm.) supports
the plane table sheet, which is securely held in position by four
metal corner clamps n, Fig. 153, Plate LXXIX.

C = camera-box (of constant focal length) made of aluminum;
T graduated horizontal circle with clamp-screw. It enables
the observer to turn the camera in azimuth by an equal
amount (panorama section) after each successive -ex-
posure;

VV= graduated metal frame;
XX = correction screws for adjusting VV to bring the principal

point into the optical axis of the camera-lens ;
b = rubber bulb for operating the pneumatic shutter of the

camera ;

/=head of pinion, which serves to elevate or depress the
camera-lens. Any such change from its normal posi-
tion may be read off on a scale with vernier, secured
at one side of the camera-lens;

d= spirit-level. Two are provided (at right angles) for
adjusting plane table M into horizontal plane (the
photographic plate will then be in vertical plane);
R = movable plate-carrier ;

LL = lever to move the plate-carrier toward the lens until the

sensitive-film surface of photograpic plate is brought

into direct contact with the graduated metal frame VV;

K = plane-table alidade with vertical circle, arranged for

stadia-reading;

Z= pivot vertically above second nodal point of camera-lens.
The lever h serves to locate the principal point /, Fig. 154,
Plate LXXIX; when the edge of the alidade ruler LL abuts
against the upturned lever h the principal ray zf, bisecting the
angle ezg, Fig. 1 54, Plate LXXIX, may be drawn upon the plane-
table sheet.

Fig. 154, Plate LXXIX, represents the plane-table top abed',
it has two pivots z and z' about which the alidade ruler LL may
be revolved.



252 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

zf = constant focal length of camera;
eg = horizontal projection of the picture trace;
ezg= horizontal angle commanded by each plate = panorama
section.

At e and g are two stops (corresponding to the ends of the
photographic field) representing the ends of- the picture trace
on the plane-table sheet.

By placing the alidade ruler LL upon the pivot z the hori-
zontal projections of lines of direction, emanating from z as a
center, to such points of the landscape which serve to orient the
picture (so-called reference points) may be drawn upon the
paper within the sector limits ezg. The point z, marked on
the sheet, may be regarded as the plotted station point. The
central pivot z' serves as vertical axis of rotation for the alidade
ruler LL when the horizontal directions to known points (signals
over trigonometric stations, visible from the camera station) are
to be plotted to locate the position of the camera station.
Point z 1 ', transferred to the plane-table sheet, is regarded as the
plotted station point.

z} or z'} is the trace of the principal plane upon the horizontal
projection plane.

The plane table M with alidade K serves to locate the camera
stations in both the vertical and horizontal sense; it may also
be utilized for the location of tertiary points with the stadia-
rod and for sketching details in the neighborhood of the sta-
tion. The horizon line and principal line may be located upon
the perspectives by means of the centimeter graduation of VV,
or two very fine wires may be attached to the corresponding
graduation marks.

The instrument rests upon the three ends of the leveling-
screws S, Fig. 153, Plate LXXIX, which fit into slots at the bot-
tom of the camera-box, the latter being firmly united with the
tripod by means of a central screw with spiral spring.

This photographic plane table is well suited for topographic
reconnaissance surveys. The results obtained with it may not be



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 253

as precise as those obtainable with the more complicated and
refined photo theodolites; still, it is more readily transported,
is very easily manipulated, and its adjustments are not subject
to frequent disturbance. The instrument is compact, well con-
ceived, and excellently executed.

The size of the photographic plate is 12X16 cm., giving an
effective picture, within the graduated margin, of 10X14 cm.

The cube- shaped camera weighs 3.5 kgr.

The packing-case (knapsack), including the entire outfit and
a stout tripod (with 3 folding legs), weighs only 11.5 kgr.

The cost of this outfit in Vienna is 400 florins.



O. Phototheodolite (" Phototacheometre ") Devised by J. and

H. Vallot.

In 1893, Joseph and Henry Vallot entered into correspond-
ence with Col. Laussedat with reference to the planning of a
phototheodolite, to be used in the topographic survey of the
Mont Blanc mountain group. The first instrument made for
this purpose did not give results with the anticipated and desired
degree of accuracy; its adjustments were found too unstable for
transportation in rough mountains.

Owing to the defects in this instrument three hundred plates
obtained in 1893 were discarded and a new phototheodolite
with a constant focal length and with vertically exposed plates
was devised. J. Vallot designed the geodetic part of the instru-
ment and H. Vallot planned the camera. The manufacture was
intrusted to Brasset Freres, who succeeded in furnishing an in-
strument of great stability, small weight, and general excellence.
It is shown in Figs. 155 and 156, Plates LXXX and LXXXI.
The latter illustrates the theodolite (" tacheometre ") and the
former represents the survey ing- camera. Both are mounted
upon the same tripod and one instrument support with hori-
zontal circle R answers for both. The following desiderata
have been fulfilled by the makers of this instrument:



254 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

First. In order to give the least resistance to the wind, to
facilitate transportation, and to reduce the price the size
of the instrument has been reduced to a minimum com-
patible with efficiency.

Second. To avoid vibration of the plate during exposure the
component parts of this instrument have been assembled
and joined together with the utmost rigidity.

Third. The instrument is well balanced to avoid strains in
the instrument itself and to give the results obtainable
with it the greatest possible accuracy.

Fourth. The geodetic parts of this phototachymeter have
been designed with a view to give results (vertical and
horizontal angles) as accurate as those obtainable with
Goulier's theodolite of 10 cm. diameter, which instrument
had been previously used for the triangulation of the
Mont Blanc group and which was now to be replaced
by this new combination instrument.

Fifth. The camera, with fixed focal length, commanding
an angle of 40 centigrades above and below the horizon,
was to be made of metal and the correct position of the
horizon line should be readily obtainable for every photo-
graphic perspective.

Sixth. The component parts of the phototachymeter have
been assembled by the makers in such a manner that all
future adjustments may be dispensed with. Any dis-
crepancy may be discovered, however, by special obser-
vations, made for testing the adjustments, which discrep-
ancies may be neutralized by applying proper corrections
to the results.

Seventh. The lens selected should be as speedy as possible
to reduce the time of exposure, and the definition of all
points falling within the unfavorable parts of the plates
should be correct within o.i mm. (The diameter of
the circle of diffusion <o.i mm.)

Eighth. If (orthochromatic) plates give better results than



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 25$

films the camera chamber should be arranged for the
use of the former. The definition should be good enough
to admit a twofold (photographic) enlargement with
no distortion to affect the accuracy of the iconometric
plotting.

Ninth. Means were to be provided to enable the operator
to inspect the field under control for each exposure with-
out having recourse to dark cloth and ground glass.
Tenth. Provision should be made to divide the panorama
automatically into sections of equal horizontal extensions.
Eleventh. The exchange of plates, when photographing a
panorama view, should be made without the least chance
of disturbing the adjustments of the instrument.
At first Carbutt's orthochromatic films were used, and it
was found that they underwent a change retraite during the
developing process, which, however, was uniform in character,
thus admitting a correction to be applied. Still, it appeared to be
desirable to avoid even such a uniform change in the dimensions
of the negatives, requiring a correction, and glass plates are now
used altogether in Vallot's work.

The orthochromatic plates are 130X180 mm. in size, with an
effective field for the perspective of 120X170 mm. These small
plates do not materially increase the weight of the outfit; one
cardboard box containing 12 plates weighs 1.4 kgr.

The double-plate holders (0.25 kgr. in weight) were made by
Balbreck. They may be inserted into the carrier and the slides
be withdrawn without imparting the least shock to the instrument.
The 1 8 double-plate holders, carried in a special packing-case,
are numbered from i to 36. The plates are marked in one corner
with a soft pencil before removal, giving series and number. For
instance : A , i to 36 ; B, i to 36, etc.

While in the field, the exposed and unexposed plates (their
plate-holders) are kept separated in the case by placing the ground-
glass frame between them. The plates used at present are
Lumiere's orthochromatic, series;! (sensitive to yellow and green).



256 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

The diagram given in Fig. 157, Plate LXXXII, represents a
vertical section through the camera chamber (in the principal
plane).

A B = nodal plane of the lens;

AC = CB = $o mm. = range of possible vertical change of
lens above or below its normal position (at C) ;
MN = effective vertical width of plate = 120 mm.;
A = extreme upper position of lens;
B = " lower " " '"
C normal or central position of lens;
A'M = B'N = i cm.;
A A' = CC' = BB' = constant focal length = 1 50 mm.

The extreme vertical angle which a plate may contain will be
found from

A'N no
tan ^^-337 - 0.733.

iA'AN=4o.3 G (centesimal graduation; 400^=360 sexagesimal
graduation).

For the extreme lower position B the greatest vertical angle would
be



and for the central or normal position C the greatest angle above
and below the horizon is found from



The horizontal field a of the plate may be found from

a 85

tan = =0.567,
2 150 D "



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 2 57

the effective width of place being = 170 mm.



= 32.8; a=6$.6 G .



If no overlaps are required a panorama may be photographed
on six plates,

6X65.6^=393.6^,

showing the omission of 6.4 of the horizon. It often will be
desirable, however, not only to photograph the entire panorama,
but also to overlap two adjoining plates. The horizon has
accordingly been divided into six equal sectors of 60^ each and a
seventh sector of 40^.

In place of the customary slide (which is either too tight or
too loose and consequently not light-tight) the camera chamber
has been provided with three openings (Oi, Oa, and O 2 , Fig. 155,
Plate LXXX), A, C, and B, Fig. 157, Plate LXXXII, into either of
which the lens may be inserted and securely held there by a
bayonet catch. The lens is secured in the middle opening Os,
Fig. 155, when the vertical angles above and below the horizon
do not surpass 26^. It is inserted at O 2 , Fig. 155, Plate LXXX
(at B, Fig. 157, Plate LXXXII), when low grounds (valleys) are
to be photographed from high elevations and at A, Fig. 157,
Plate LXXXII, when mountain peaks are to be photographed
from lower stations.

The horizon line for each of these three positions of the lens is
located on the negatives by a set of two projecting points />, Fig. 155,
Plate LXXX, which are photographed on every plate.

When great differences in altitude are to be recorded, two
plates may be exposed in the same direction and from the same
station, one with the lens at A, the other with the lens at B, Fig.
1 5 7, Plate LXXXII.

The openings Oi and O 2 , Fig. 155, Plate LXXX, are closed by
caps which have the same bayonet catch as the lens mount O^.



258 PHOTOTOPOGRAPH1C METHODS AND INSTRUMENTS.

The objective is an anastigmat of Zeiss, No. 2, series Ilia,
with revolving diaphragm and stop No. 5 ( ) . This lens is made

of Jena glassby Krauss in France, and it has a constant focal
length of 150 mm.

Enlargements of the negatives 50X60 mm. give very good
results for the iconometric plotting, which has been done on
scale i : 20000 for the Mont Blanc survey.

Behind the lens a yellow (plate) glass screen has been in-
serted with a tint sufficiently dark to necessitate the length of
exposure required for the normal plate to be increased fifteen times.
The insertion of this screen increases the focal length of the ob-
jective to 151 mm., the yellow light- rays being less refracted than
the blue and violet rays. This camera is not provided with an
instantaneous shutter, as the exposure will always require several
seconds.

The tripod is made of oak and it may be folded together to
0.75 m. length. On rocky peaks, where the unfolded tripod
would be too long or where it would require too much ground
space, it may be used in its folded condition.

The tripod head H, Figs. 155 and 156, Plates LXXX and
LXXXI, is made of aluminum, which metal enters greatly into
the composition of this instrument. The camera chamber and
lens-hole caps O\ and O 2 , Fig. 155, Plate LXXX, are also made
of aluminum.

The horizontal circle and metal instrument support resembles
in form the horizontal circle adopted for the tachymeter-theodo-
lites used by the Genie Corps of France. The three leveling-screws
L, Figs. 155 and 156, Plates LXXX and LXXXI, set into the
three arms A, are on the circumference of a circle of 0.17 m. in
diameter.

The horizontal circle R, Figs. 155 and 156, Plates LXXX and
LXXXI, is o.io m. in diameter and is mounted above the
circular disc F which supports the cross-levels l\ and /2> used for
leveling the instrument.



_UFOj
SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 259

Its graduation (centesimal 400^=360 sexagesimal) is on the
vertical (outer) cylindrical surface, and it may easily be read
when the camera is mounted on the instrument support.

A conical pinion (in the prolongation of the verticaraxis) on
the horizontal circle serves to support the camera or the tachym-
eter-theodolite, which are provided with conical bearings to fit
this conical pinion.

A special arrangement with stops insures the uniform azi-
muthal swings of the camera when exposing the plates forming
a complete panorama; six of these plates cover an angle of 60^
each and the seventh controls 40^ of the horizon. Each plate
covers or overlaps the adjoining one by a common margin of
15 mm. in w r idth. When used as a theodolite the arresting stops
may be set inactive.

The definition of the photographic perspectives for all objects
from 10 m. to infinite distance is very clear (using stop No. 5).

A tele-objective (long-distance objective) has been provided
by means of which circular pictures may be obtained on the plate
of o.i i m. diameter and with a two and one half fold enlargement.

The metal points p and f, Fig. 155, Plate LXXX, have cir-
cular openings of i mm. diameter which serve to locate the
horizon and the principal line on such pictures where the image
of the plate has been obscured by the tint of the image close to



Online LibraryJohn Adolphus FlemerAn elementary treatise on phototopographic methods and instruments, including a concise review of executed phototopographic surveys and of publicatins on this subject → online text (page 20 of 33)