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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 21 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 21 of 33)
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the point.

Blackened diaphragms D, Fig. 155, Plate LXXX, are inserted
into the darkened chamber to intercept all side-light rays that
may be reflected into the camera and cause the plate to be
fogged.

The heads of the three screws 5, Fig. 155, Plate LXXX,
used to secure the camera in its position on the horizontal circle,
are corrugated or checked and well blackened to prevent side
reflections of light-rays from their surfaces.

The ground -glass plate is used only when testing the adjust-
ments of this instrument.

The upper face of the camera is provided with three sight-



260 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

frames FI, 2, and FS, which may be revolved about their
lower ends to lay perfectly flat on the camera top when not in
use.

Two 'vertical planes containing Fi, F 2 , and FiF 3 include a
horizontal angle of 60^, the extreme width of the horizontal
field for one plate. The sight-frame FI (near the lens) is pro-
vided with a vertical wire and the sight- frames F 2 and FS (at
the back of the camera, Fig. 155, Plate LXXX) have three
peep-sights each, which, together with the metal bridges of FI,
are disposed at such distances to correspond with the vertical
angles, commanded by the lens on the plate, for the three differ-
ent positions that may be given the lens. By sighting through
the three peep-sights it may readily be determined into which
one of the three openings (Oi, O 3 , O 2 , Fig. 155, Plate LXXX) the
lens should be inserted to control the extension of a certain pan-
orama section in the vertical sense.

For executing the tertiary triangulation and for locating
detached camera stations (stations not already included in the
triangulation scheme) the surveying-camera, Fig. 155, Plate
LXXX, may be converted into a tachymeter-theodolite by replac-
ing the camera by an " alidade holometrique " with " broken "
telescope, ab, Fig. 156, Plate LXXXI, like that of Col. Gou-
lier's pattern (with the exception that the ruler has been dis-
carded here). The base of this tachymeter has three screws 5,
Fig. 156, Plate LXXXI, corresponding with those of the camera,
to secure it to the horizontal circle.

The telescope, which magnifies about twelve times, is "broken"
to facilitate the measuring of large vertical angles. A finder e,
Fig. 156, Plate LXXXI, of a fourfold magnifying power is pro-
vided. It has the same form as the telescope ab.

Vertical angles are measured with the vertical circle E
(" reclimetre"), Fig. 156, Plate LXXXI, which has a diameter
of 0.08 m. and reads to single grades (quadricentesimal gradu-
ation).

A special level is supplied to facilitate the ready adjustment



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 261

of the telescope ab into horizontal plane when this tachymeter
is to be used as a spirit-level.

This entire phototachymeter (excluding the tripod) is packed
into a box having three compartments, which may be closed by
two doors like a wardrobe. One compartment contains the
tachymeter proper (" Teclimetre ") ET, Fig. 156, Plate LXXXI,
the other receives the camera C, Fig. 155, Plate LXXX, and
the third is reserved for the repeating circle R with its support A y
Figs. 155 and 156, Plates LXXX and LXXXI.

The folding tripod, together with a light folding stadia or
telemeter-rod, is carried in a separate packing-case. All pack-
ing-cases are covered with rubber cloth to guard against the
evil effects of dampness.

This entire instrument outfit may be strapped to a light
packing-frame, making a compact pack to be carried on the back.

The weight of this outfit has been distributed as follows:

Complete phototachymeter 5.3 kgr.

Packing-case and accessories 3.6 ' '

Water-proof case, including straps 0.8 ' '

Folding tripod 4.8 "

Folding stadia-rod 0.8 "

Water-proof case for both, including straps ... 0.7 "

Total weight of instruments 16 kgr.

Packing-frame, including straps 2 "

Total weight to be borne by one packer. . . 18 kgr.

The 1 8 double-plate holders (including 3 doz. plates) weigh
9 kgr.; they are stored in a wooden case which Weighs 3.5 kgr.,
including the water-proof covering. These 12.5 kgr. are carried
by a second packer who has additional implements to take,
bringing the weight of his pack also up to 18 kgr.

For the ' survey of Mont Blanc it has been found that 36
plates fully suffice for a day's work. For a trip of several days'



262 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

duration the observer carries extra plates (in their cardboard
boxes, but stowed away in a separate water-proof packing-case),
which are exchanged every night, using a small folding ruby
light and portable dark tent.

In 1894 four hundred negatives were obtained by Vallot
Bros., and in 1895 tne number reached over 500. The season
of 1896 was so misty and rainy that few da)?s were available
for this work, the mountain peaks being rarely visible, and also
lower parts of the mountains being more generally hidden from
view in a dense fog. This season's results again proved the value
of the phototopographic .method above all others for surveys
in the higher altitudes of mountainous regions, as the results
obtained during the short periods of good weather could not
have been acquired in the short time available by any other
known topographic method.

The area of this survey is controlled by 300 triangulation
points (established between 1894 and 1896) which are connected
with a base line at Chamounix of 1785.824 m. length.

P. Phototheodolite Designed by J. Bridges-Lee.

This instrument has been patented in England and other
countries, and it is made by Louis P. Casella, who has published
a full description of the same, with instructions for its use in
the field (Description of a New Phototheodolite designed by J.
Bridges-Lee, Esq., M.A., F.G.S., etc. With full instructions
as to its manipulation in the field. L. Casella, maker to the
Admiralty, Ordnance, etc., No. 147 Holborn Bars, London,
E. C.), from which the following description has been abstracted:

This phototheodolite is shown in Figs. 158 and 159, Plates
LXXXIII and LXXXIV, the latter representing a view of the
interior of the camera-box, the ground-glass plate H having
been turned down. It will be noted that this instrument com-
prises :

(i) A complete, well-made theodolite reading to minutes;



SURVEYING-CAMERAS AND GEODET C INSTRUMENTS. 263

(2) A photographic outfit answering all ordinary demands;

(3) A good and large azimuth compass, its vertical scale

admitting of very close readings to be made either
through the rear window h' or through the lens B.
The combination of these three instruments into a symmetrical
well-made phototheodolite makes this one of the most generally
useful instruments that an explorer of unknown regions can
add to his instrumental outfit.

With reference to Figs. 158 and 159, Plates LXXXIII and
LXXXIV, we have:

A. Rectangular camera-box made of aluminum (cast metal);
its upper face supports the telescope E, with vertical circle F
reading to minutes. This box is permanently attached to
the leveling support T, Fig. 158, Plate LXXXIII.

B. Rectilinear photographic lens of excellent quality and sup-
plied with iris diaphragm. No focusing adjustments are
provided for this lens, and it should be set by the instru-
ment-maker very accurately in correct position with refer-
ence to the other parts of the instrument.

A second photographic lens, movable in a sleeve with rack-
and-pinion focusing adjustment, will be supplied if the instru-
ment is to be used for ordinary photographic work at short dis-
tances.

C. Horizontal circle, graduated to half degrees with vernier
reading to single minutes.

The vernier is attached to the rear of the camera, Fig. 159,
Plate LXXXIV, its zero mark falling into the same vertical
plane which passes through the optical axis of the camera-lens.

D. Tribrach, or triangular piece connecting tripod head and
camera. It supports the terminating heads at the base
ends of the three leveling- screws. To insure stability the
terminal feet of the levelling-screws may be secured to the
tribrach by means of the usual locking-plate connected
with the tribrach.

E. Telescope with cross- and stadia-inches in the body and



264 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

general adjustments for a surveying- telescope. The tele-
scope is mounted like that of a plane-table alidade to be
rotated about a horizontal axis in a vertical plane only. Its
plane of transit contains the optical axis of the camera-lens,
the zero mark of the vernier of the horizontal circle, the ver-
tical hair K, as well as the vertical axis of the needle sup-
port of the azimuth compass, when the instrument is in
adjust ment and leveled.

F. Vertical circle, graduated into half-degrees, firmly con-
nected with the telescope and provided with a fixed vernier
reading to single minutes. This circle controls a vertical
range sufficient for all ordinary topographic surveying pur-
poses.

G. Tubular spirit-level revolvable in a low cylindrical case
firmly attached to and sunken into the upper face of the
aluminum camera-box. This level serves to give the top
of the camera-box a horizontal position when the camera
has been oriented for an exposure to be made. This adjust-
ment is made in the usual manner by means of three leveling -
screws supporting the instrument on the tribrach.

H. Back of the camera containing the ground glass h and sup-
plied with hinges to enable the operator to swing the ground
glass back, as shown in Fig. 159, Plate LXXXIV. A win-
dow h' of polished glass is inserted into the ground glass h
to enable the surveyor to observe the vertical index hair K
and coincident graduation mark of the vertical compass
scale, with or without the use of the microscope O.
I. Rectangular metal frame supplied with stout backstays
(not visible in the illustrations) and securely attached to the
bottom plate which supports the compass box M. This
bottom plate may be moved in the direction of the axis
of the camera-lens, sliding on guides rigidly fixed to the
bottom of the camera-box.

When the camera is to be used for ordinary photographic
purposes the bottom plate (including the frame I and azi-



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 265

muth compass) may be withdrawn and laid aside. A square
piece of black velvet is provided to be placed upon the metal
bottom of the camera- box. After the insertion of the second
lens with adjustable focal length the camera will be ready
to be used for photographing near objects.

The. rear surfaces of the frame / are in vertical plane
which is perpendicular to the optical axis of the camera-
lens when the instrument is leveled and in perfect adjust-
ment.

jj. Transverse pinion extending across the bottom of the camera-
box and terminating in two milled heads JJ. The frame /
may be racked backwards or forwards by a corresponding
turning of the milled heads //.

Pointers are attached to the milled heads, which serve
to indicate whether the internal structures are in the forward
or backward position when the falling back of the camera-
box has been let down to allow a double-plate holder to be
inserted into the camera.

The dimensions of -the rectangular frame / are such that
it can be racked back (entering the plate-holder frame) to be
brought into direct contact with the sensitized film of the photo-
graphic dry-plate, when the cross-hairs K and K' will also actually
touch the film. Of course, the slide protecting the photographic
plate against light should be first removed before the frame /
is racked back. Two small stops in the form of sliding bolts
(not shown in the illustrations) are provided to prevent the frame 1
from being carried back too far or with too much force and
to secure uniformity of the focal length for all phototopographic-
plate exposures.

K. Vertical hair passing through two round holes in the frame
/ and held in position by means of small wooden pegs.
When broken, a new hair can readily be inserted into the
holes and secured by small pegs. This hair serves to mark
on the negative the median vertical plane of the instrument
and the principal line of the photographic perspective. It



266 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

cuts the optical axis of the camera-lens at right angles and
it serves as index mark when the compass scale is read.
It is in the same plane as the vertical web in the telescope,
the optical axis of camera-lens, the vertical axis of revolu-
tion of the azimuth compass, and the zero mark of the vernier
of the horizontal circle.

K'. Horizontal hair secured to the frame in the same manner
as hair K. The point of intersection of both hairs is in
the optical axis of the camera-lens, and on the negative it
marks the principal point of the photographic perspective.
When the camera is in perfect adjustment and accurately
leveled the shadowgraph of K' on the negative will bisect
points having the same height as the optical axis of the
camera at the station whence the picture was taken.

The proper location of the small holes in the frame /,
fixing the position of the hairs K and K', is ascertained by
the maker.

LL. Small tablets of transparent celluloid or xylonite. They
serve to receive notes giving particulars concerning station
mark, barometric reading, or determined elevation of camera
station, number of plate, time of exposure, etc., which it
may be desirable to record photographically, as shadow-
graphs, on the picture. Such notes are written upon the
tablets LL in the ordinary way with quick-drying ink.
The tablets when dry are placed upside down in small pock-
ets in the frame and the notes appear as shadowgraphs in
the corners bordering the sky portion of the negative.

M. Magnetic azimuth compass with vertical cylindrical trans-
parent scale, graduated to half degrees from o to 360.
This transparent scale in its revolution passes quite close
to the vertical index hair K, without ever touching it, how-
ever. The pivot of the compass is permanently secured
to the base or bottom plate already referred to, so that the
cylindrical compass-scale is always at exactly the same
distance from the vertical hair K.



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 267

When the bottom plate supporting the frame / and com-
pass M is racked forward in the camera-box, a copper disc
is automatically raised, lifting the agate cup and pressing it against
the support m so that the compass is firmly clamped, preventing
injury to the pivot and other parts of the compass during trans-
portation. When the bottom plate is racked back to bring the
cross-hairs K and K r into contact with the sensitive film of a
photographic plate, the agate cup is lowered (automatically)
upon the pivot and the magnetic compass assumes its natural
position. The compass graduation being on a transparent
cylinder, the magnetic azimuth of the principal line of every
exposed plate wilLbe recorded photographically in the sky region
of the negative as a shadowgraph.

N. Catch to hold the double-plate holder in place when inserted
into the camera. The frame of aluminum forming the
rear of the camera-box is faced with black velvet to guard
against the entry of extraneous light when the double-
plate holder is in position.

O. Microscope with universal joint movement to permit of
its being used either for reading the observed horizontal
angles (on the horizontal circle C with vernier), or for read-
ing the compass bearings through the window h f in the
ground-glass back h.

P. Adjustable microscope for reading vertical angles.
Q. Clamp- and tangent-screw for arresting azimuthal or hori-
zontal circle and giving it slow motion.
R. Clamp- and tangent-screw for camera.
5. Clamp- and tangent-screw for telescope.
T. Strong aluminum head of tripod with bronze clamping-
screws for folding legs. It is supplied with transverse bars
(not shown in the illustrations) of bronze, serving as attach-
ments for chains to safeguard the instrument when in posi-
tion at a station. These bars also serve to receive the hooks
attached. to a net into which heavy stones may be placed



268 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

to give stability and steadiness to the instrument when used

in windy weather.
U. Two cross-marks on the top of the box. Their distance

indicates for ordinary temperatures the permanent focal

length of the camera, to be used for the negatives.
A small hook for the attachment of a small plummet is secured
to the tripod head T in the central axial line of the instrument.
The telescope is supplied with an erecting as well as an inverting
eyepiece.

A color-screen of optically worked green glass may be fitted
inside the sunshade of the photographic lens. Yellow or orange
glass can also be supplied when desired.

Attached to the frame / (which carries the hairs) is a hori-
zontal transparent scale of angular distances (Fig. 159, Plate
LXXXIV), photographically prepared by aid of the identical
lens and instrument which it accompanies. It is used for sur-
veying purposes, as with its aid the exact angular distances of
points in the picture to the right or left of the principal vertical
plane may be read off directly with the aid of parallel rulers.
This scale also facilitates the determination of compass errors,
because if there are any points in a picture whose true bearings
have been fixed with precision trigonometrically or otherwise
it is only necessary to add or subtract the angular distances of
those points, as read on the horizontal scale of angles, to or
from the photographiccally recorded compass-bearings of the
points, and the difference between the compass- bearings and
the true bearings is the compass variation. This simple verifi-
cation can be performed in office at any time. This instru-
ment is supplied with 6 double-plate holders of good construction,
to carry one dozen plates, size 5X4 in., either horizontally or
vertically.

It fits easily and securely in a strong, well-made, brass-bound
mahogany case with catches, lock, and key.

The double-plate holders, extra eyepiece, extra camera-lens :
color-screen, and plumb-bob all fit in the same case, which for



SURVEYING-CAMERAS AND GEODETIC INSTRUMENTS. 269

greater security and convenience of transportation is placed into
an outer sole-leather case with pack-straps.

The tripod head is provided with a metal screw-cap, a suit-
able protecting cover of its own, and the legs can be strapped
together for easy transportation.



CHAPTER IX.
PANORAMA CAMERAS.

THE older lens types gave correct perspectives only for small
angles, rarely exceeding 30 degrees, and Martens in Paris was
probably the first to devise a so-called panorama camera capable
of photographing wider sections of the horizon on one plate,
with lenses that ordinarily would cover but a small angular field.
He solved this problem by constructing a hemi-cylindrical camera
with a revolvable lens plate. If the objects are far enough away
to permit the use of a constant focal length of lens, and if the
lens may be rotated about a vertical axis in the second nodal
point of the lens system, panorama views may be obtained on a
sensitized surface of a daguerreotype plate bent into a half-cylinder
whose radius equals the constant focal length of the lens and
whose axis coincides with the vertical passing through the second
nodal point of the camera-lens.

I. The Photographic Plane Table Devised by A. Chevallier (1858).

Chevallier's " planchette photographique " may be men-
tioned here, as, in a certain sense, it also is a panoramic camera.
In this instrument the entire panorama view was continuous
and found representation on a single plate; the latter, however,
was exposed in the horizontal plane. The lens axis being hori-
zontal, a prism had to be interposed between plate and lens to
bring the image into the horizontal picture plane. All verticals
of the landscape converged to one point, the center of the cir-
cular horizon line. For further deails of this historically inter-

270



THE ROCKWOOD-SHALLENBERGER PANORAMIC CAMERA. 271

esting instrument we would refer to the publications on this sub-
ject given under French phototopographic literature.

II. The Rockwood-Shallenberger Panoramic Camera.

A horizontal section through this camera (made just above
the camera-lens) is represented in Fig. 160, Plate LXXXII. It
practically consists of two cameras C and c. The latter (smaller)
one contains the lens O and is revolvable about a vertical axis
passing through the latter. The main camera-box C forms a
semi-cylinder with a sensitive film stretched over the inner cylin-
drical surface, and that may be unwound from the magazine
roller B passing to the receiving roller A after exposure. As
the small camera is revolved, the light-rays entering the lens,
act upon a narrow vertical strip of the film at a time. The con-
nection between the objective end of the small camera c with
the front board b of the main camera C is accomplished by means
of a pliable light-tight fabric e. The lens O has a long focus
and the panoramic perspective is entirely free from distortion,
only a vertical strip of one quarter inch width being exposed at
one time. The pictures are 8X40 inches and it takes from
three to five seconds for the lens to complete one revolution of
1 80 degrees. The speed in the swing of the smaller camera
is controlled by a clockwork, the rate of which may be increased
or retarded at pleasure, with due reference to the changes in
atmospheric conditions and character of subject.

III. R. Moessard's Topographic Cylindrograph.

The so-called cylindrograph of R. Moessard (commandant
du Genie, attache au Service geographique de 1'armee) is
similar in construction to the apparatus just described; this
instrument, however, is specially devised for surveying purposes.

The semi-cylindrical camera-box, Fig. 161, Plate LXXXY,
rests upon a tripod with leveling-screws to adjust the vertically
of the axis of revolution aa of the camera lens O, which axis coin-



272 PHOTOTOPOGRAPHIC METHODS AND INSTRUMENTS.

cides with the axis of the half-cylinder, formed by the surface
of the sensitive film. For focusing purposes the latter may
be replaced by a semi-cylindrical ground-glass plate. By using
the sight-ruler 5 as a lever the camera-lens O may be rotated
about aa, allowing the speed of motion to be controlled by the
illumination of the landscape. By carefully examining the
panorama through PP' while aa is being moved in azimuth,
the correct timing for the exposures of the different panorama
strips may be made. The space between the frame RR is filled
in with a soft and light-tight fabric, allowing an easy play for
the rotation of the objective O.

The upper surface of the topographic cylindrograph is pro-
vided with an azimuth compass C and a set of cross-levels A
and B. The bent frame forming the guide for the film is sup-
plied with graduations on the inner edges which form the mar-
gins of the panoramas. The divisions of the upper and the
lower scales (horizontal) correspond to degrees in arc, while
the divisions of the vertical marginal ends are graduated to read :

- , where / = constant focal length of the lens O ( = radius of

the cylindrical sensitive surface of the film). Four movable
indices are provided; two of these, H and H', Fig. 162, Plate
LXXXVI, serve to mark the horizon line of the half-panorama
and the other two, N and E, serve to indicate the magnetic
meridian and the magnetic east and west line, respectively,
for each panorama view. The proper placing of the indices
for each half-panorama may be accomplished by means of the
azimuth compass C and sight-ruler or alidade S. Thus the mag-
netic azimuths of horizontal directions may be taken directly
from the picture.

The vertical angles are readily found by means of the ordinates
of the pictured points (above or below the horizon line HH')
measured hi one hundredths of the focal length /, using the photo-
graphed scales on the vertical margins of the pictures for this
purpose.



R. MOESSARD'S TOPOGRAPHIC CYLINDROGRAPH. 273

For instance, the angle of depression of the ray Oa (to the
foot of the pictured tree a, Fig. 162, Plate LXXXVI) is found

from

aa!
tan'=-p

or when aa' is measured on the side scale and found to be 2 5 parts,

aa'

tan 3 = =0.25.

100

To determine whether the levels A and B, Figs. 161 and 163,
Plates LXXXV and LXXXVI, read zero when the cylindrical
film is vertical, and also to ascertain whether the indices H and H' y
Fig. 162, Plate LXXXVI, representing the horizon line are cor-



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 21 of 33)