Improvements in Instruments for Surveying with the Aid of Photography.
Year: 1896

page_text: Date of Application, 23rd Sept., 1896
Complete Spanifention
1005
PROVISIONAL SPECIFICATION.
Improvements in Instruments for Surveying with the Aid of
Photography.
JOIN BRIDGES LEE M.A., F.G.S., Barrister-at-Law, of the Inner Temple, Present
Address, 4 Harcourt Buildings Temple London, E.C., do hereby declare the nature
of this invention to be as follows:-
This Invention relates to improvements in Instruments for surveying with the
aid of Photography and more especially to such Instruments as are described in
my specifications Nos. 11,958 and 14,460 of 1894.
The first improvement consists in the construction and use inside the camera
of fixed scales engraved or otherwise marked on strips of thin transparent material
(such as celluloid glass or mica or other suitable substance) each strip being
divided so as to form an accurate scale of angular distances from the medium
vertical plane as marked by the vertical fibre. The scale is in every case_con-
structed with special reference to the focal length of the particular lens employed
with the camera and it is divided right and left from the central mark which is
zero. The divisions right and left mark degrees and fractions of a degree of diver-
gence from the central mark. I attach this divided transparent scale horizontally
to the face of the rectangular frame (f2 in the drawings attached to the
specifications above referred to) so that when the frame is racked back into the
dark slide the divided strip shall be brought into actual or approximate contact
with the photographically sensitive surface of the plate or film.
The
The surface on which the scale divisions are marked should be that surface
which is towards the photographically sensitive surface and the strip should be
inverted so that the figures may print out normally from the negatives.
position in which I prefer to affix the horizontal divided scale is a little higher
up on the frame than the level of the transparent compass scale so that it may
print out immediately below that scale when the picture is right side up.
When the transparent scale has been accurately constructed and fixed in the
instrument as above described every picture taken will carry upon its face all
the elements necessary to determine with ease and accuracy the angular distances
and bearings of every visible point and a degree of precision in the measurement
can be obtained such as has never before been attempted in Photogrammistry.
The pictures will also possess this very great advantage that when they are
enlarged by magic lantern projection or otherwise the scale will be magnified
in exactly the same proportion as the picture and remarkably accurate determina-
tions of angles can be obtained.
Ordinarily I would only employ one horizontal scale in each camera in the sky
region as described.
Referring to what I have described as the first improvement in this provisional
specification I am of opinion as at present advised that the best method for con-
structing the scales therein referred to will be a photographic method using in
each case for the photographic preparation of the scale the particular lens whose

page_text: pictures the scale will afterwards serve to measure but I do not wish to confine
myself to the photographic method of construction because the scales can also be
mathematically calculated or they can be prepared by projection.
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1800
COMPLETE SPECIFICATION.
Improvements in Instruments for Surveying with the Aid of
Photography.
JOHN BRIDGES LEE M.A., F.G.S., Barrister-at-Law of the Inner Temple, Address
6 Kings Bench Walk (late 4 Harcourt Buildings) Temple, London, E.C., do hereby
declare the nature of this invention and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:-
This invention relates to improvements in Photographic Surveying apparatus.
In my patent specifications Nos. 11,958 and 14,460 of 1894 I have shewn and
described how to obtain photographic pictures which bear on their faces automatic
records of traces of (a) the median vertical (or principal) plane (b) the horizon
plane of the instrument (c) the principal point of the perspective and (d) the
magnetic bearing of the principal plane.
In addition to the mechanism described in the specifications aforesaid I now use
a tangent scale of horizontal angular distances from the principal plane which
I prepare photographically and affix horizontally to the frame f which is shewn
and described in those specifications.
To prepare the scale I take a long band of white paper or other suitable material
and after ruling a perpendicular line across the band at about the middle of its
length I set off right and left a number of parallel lines exactly three inches apart
and number these right and left 1° 2° 3° and so on to represent degrees of angle.
All the lines should be ruled with a dead black ink and the lines which correspond
to 5°, 10°, 15°, 20°, 25° I make longer and thicker than the lines which mark
intermediate degrees. I then divide the degree spaces into halves and quarters
by lines of suitable length and thickness and mark these 151, 30', 45' right and left
from the middle or zero line.
The sizes of the figures I make to correspond with the thickness of the lines.
I then sub-divide the quarter degree intervals into thirds so as to obtain 5 minute
intervals all along the scale. These 5 minute intervals may be still further sub-
divided by very fine lines to give single minute intervals if desired.
To a very large extent the details of construction of this large scale may be varied
to suit different tastes but the important point to observe is that it should in
any case be a scale of uniform linear distances.
Having prepared this large black and white scale I mount it upon the inner
concave surface of a segment of a cylindrical ring of wood or masonry whose
radius is 14ft. 39 inches and I set up the camera so that the optical centre of
the photographic lens shall be at the geometrical centre of that cylindrical ring
when the image of the zero line of the scale is in the principal plane. I level
the scale to be photographed and level the camera and make sure that the zero
line of the scale is in the same plane with the vertical wel of the telescope and
the vertical hair inside the camera. I take care also to rack back the internal
structures so far as they will go and to close the iris diaphragm to a very small

page_text: aperture and then all being ready I make an exposure and develop a negative in
the usual way.
From this negative I print a positive on a transparency plate of glass. This
positive photographic scale I cut out with a diamond from the rest of the plate
and I then affix the scale to the frame f2 with the figures upside down and the
film surface facing backwards, and the zero line exactly in the median vertical
plane. The film surface should be exactly flush with the back surface of the
frame f. This position is obtained by fixing the ends of the glass scale in recesses
in the frame of exactly the right depth.
The best position for the scale is as low down upon the frame as it can be placed
without interfering with projections of the compass scale.
If the foregoing directions have been carefully carried out the camera will
now yield pictures which will differ from the pictures yielded by the instrument
figured and described in my specification No. 14,460 of 1894 in so far as they will
in addition have recorded upon their faces (in the sky region and immediately
below the compass scale) a horizontal scale of angular distances from the principal
plane of the picture. This scale having been photographed by the identical lens
in the same focal plane it should be always reliable and with the aid of a parallel
ruler it will serve to indicate without trouble the angular bearing of any point
visible in the picture. Also whenever the picture is enlarged the scale will be
enlarged with it and always ready and in place for making any desired measure-
ments.
In the foregoing description I have described the construction of a photographic
tangent scale from a cylindrical scale with 3 inch intervals to a degree of angle.
It is evident that on the same principal more or less open scales can be used
provided always that the radial distance is correspondingly varied.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that what I
claim is:-
1. The use of a transparent scale of angular distances inside a photographic
camera in such position that it can be firmly held in close contact against the
surface of a photographically sensitive plate when an exposure is made for the
purpose of taking a picture."
2. The method of construction substantially as herein described.
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