Year: 1896

page_text: I, RALPHI SADLER, of Earlswood Villa, Upper Clapton, in the County of London,
Civil Engineer, do hereby declare the nature of this invention to be as follows:-
This instrument may be used for all the ordinary purposes of a Range Finder
and otherwise for measuring distances, and is particularly adapted for use in
surveying when. filling in detail with the plane table in which operation it enables
the distance of an object to be ascertained and (its direction being known) its
absolute position to be fixed.
The first necessity for ascertaining by observation the distance of an object is to
obtain a clear and well defined view of it such for instance as would be obtain-
able by the use of a Telescope, but as an ordinary Telescope of any power is of
itself a somewhat cumbersome instrument, something mora portable and con-
venient is required.
This is provided for in the present invention by a modification of an ordinary
Field Glass or Galilean Telescope, comprising the substitution for the simple con-
cave lens hitherto used as an eye piece, of a compound lens of crown and flint
glass corrected for both spherical and chromatic aberation.
By employing such an eye piece and by the consequent elimination of the
chromatic and spherical aberation it is possible to produce an instrument of
greater magnifying power without unduly contracting the field of view, and as
such an eye piece may be made to take a very wide angle I am able to use a much
larger object glass than is usual without increasing its focal length.
The general arrangement of such a telescope comprises a compound object glass
of the usual achromatic construction and of shont focal length as compared with
its diameter, and an eye piece or lens compounded of flint and crown glass or
equivalent material arranged, to correct the aberations before mentioned, the
distance between the object glass and eye lens being about equal to the difference
in their focal lengths.
The Range Finding portion of the apparatus comprises a reflecting prism or a
plane mirror placed in front of, and covering half of, the said object glass, and
with the reflecting surface at an angle of 450 with the axis of the telescope. An
arm or bracket fixed at right angles to the telescope carries a mirror the reflecting
surface of which is nearly parallel with that of the first named mirror, and facing
it, and this mirror is mounted so as to be capable of rotation through a small arc,
and such rotary motion is given it and indicated by an indicator-arm arranged to
read on an arc divided to show distances or otherwise.
The motion of the indicator arm is not communicated direct to the mirror but
is reduced by any well known or other mechanical arrangement so that a con-
siderable motion of the indicator arm turns the mirror through only an extremely
small angle.
The operation of this instrument is as follows:-
The light rays from any distant obiect falling on the uncovered half of the

page_text: object glass pass directly through the telescope to the observer's eye. Another
portion of the rays falling on the movable mirror are reflected therefrom to the
mirror which is in front of half the object glass and thence through the telescope
to form a second image in the eye. If the mirrors are parallel and the object is at
an indefinite distance, or at so great a distance that the rays are practically
parallel, the two images will be coincident and the object will be seen as if the
mirrors were removed, but if the object be at a comparatively short distance the
images will not coincide and the object will appear double. If then the movable
mirror is turned by means of the indicator arm until the two images coincide the
distance of the object from the observer may be read on the scale of the graduated
arc opposite the end of the indicator arm.
The working of the instrument depends upon the following fact. Supposing
the indicator arm to stand at zero when the mirrors are parallel, the angle through
which the movable mirror requires to be rotated in order that the two images may
coincide will be half the angle subtended at the object by the distance between
the mirrors. For some purposes it may be found preferable to divide the arc into
degrees and fractions to show the angle through which the mirror has been
rotated, which might be read with great exactness with the help of a vernier.
The distance of the object would then be ascertained by reference to a table cal-
culated for the particular instrument in use, as it would depend (supposing the
adjustments to be perfect,) upon the distance between the mirrors. It may be
found advisable for some purposes where portability and promptness in obtaining
the result are not of primary importance to construct an instrument with a
distance of two or several feet between the mirrors; in which case even consider-
able distances might be determined pretty accurately. Such an instrument would
doubtless facilitate the mapping of detail in a rough country across which
measurements would be difficult. In each case the distance obtained would be
the distance between the object and the mirrors, and if the object observed were
above or below the instrument the angle of elevation or depression would require
to be read and the horizontal distance would be deduced by calculation.
The improved form of Galilean telescope indicated is suited for use as a
reconnoitring telescope; for which use it is well adapted where high magnifying
power is not required.
Dated the Fourth day of December 1896.
NEWNHAM BROWNE,
Agent for the Applicant.
I, RALPH SADLER, of Earlswood Villa, Upper Clapton, in the County of London,
Civil Engineer do hereby declare the nature of this invention and in what manner
the same is to be performed to be particularly described and ascertained in and by
the following statement:-
This instrument may be used for all the ordinary purposes of a Range Finder
and otherwise for measuring distances, and is particularly adapted for use in
surveying when filling in detail with the plane table in which operation it enables
the distance of an object to be ascertained and (its direction being known) its
absolute position to be fixed.
The first necessity for ascertaining by observation the distance of an object is to
obtain a clear and well defined view of it such for instance as would be obtain-
able by the use of a Telescope but as an ordinary Telescope of any power is of

page_text: itself a somewhat cumbersome instrument something more portable and con-
venient is required.
This is provided for in the present invention by a modification of an ordinary
Field Glass or Galilean Telescope, comprising the substitution for the simple con-
cave lens hitherto used as an eye piece, of a compound lens of crown and flint
glass corrected for both spherical and chromatic aberation.
By employing such an eye piece and by the consequent elimination of the
chromatic and spherical aberation it is possible to produce an instrument of
greater magnifying power without unduly contracting the field of view and as
such an eye piece may be made to take a very wide angle I am able to use a much
larger object glass than is usual without increasing its focal length.
The general arrangement of such a telescope comprises a compound object glass
of the usual achromatic construction and of short focal length as compared with
its diameter, and an eye piece or lens compounded of flint and crown glass or
equivalent material arranged to correct the aberation before mentioned the
distance between the object glass and the eye lens being about equal to the
difference in their focal length.
The Range Finding portion of the apparatus comprises a reflecting prism or a
plane mirror placed in front of, and covering half of, the said object glass, and
with the reflecting surface at an angle of 450 with the axis if the telescope. An
arm or bracket fixed at right angles to the telescope carries a mirror the reflecting
surface of which is nearly parallel with that of the first named mirror, and facing
it, and this mirror is mounted so as to be capable of rotation through a small arc,
and such rotary motion is given it and indicated by an indicator-arm arranged to
read on an arc divided to show distances or otherwise.
The motion of the indicator arm is not communicated direct to the mirror but
is reduced by any well known or other mechanical arrangement so that a con-
siderable motion of the indicator arm turns the mirror through only an extremely
small angle.
The operation of this instrument is as follows:―
The light rays from any distant object falling on the uncovered half of the
object glass pass directly through the telescope to the observer's eye. Another
portion of the rays falling on the movable mirror are reflected therefrom to the
mirror which is in front of half the object glass and thence through the telescope
to form a second image in the eye. If the mirrors are parallel and the object is at
an infinite distance, or at so great a distance that the rays are practically
parallel, the two images will be coincident and the object will be seen as if the
mirrors were removed, but if the object be at a comparatively short distance the
images will not coincide and the object will appear double. If then the movable
mirror is turned by means of the indicator arm until the two images coincide the
distance of the object from the observer may be read on the scale of the graduated
arc opposite the end of the indicator arm.
The working of the instrument depends upon the following fact. Supposing
the indicator arm to stand at zero when the mirrors are parallel, the angle through
which the movable mirror requires to be rotated in order that the two images may
coincide will be half the angle subtended at the object by the distance between
the mirrors. For some purposes it may be found preferable to divide the arc into
degrees and fractions to show the angle through which the mirror has been
rotated, which might be read with great exactness with the help of a vernier..
The distance of the object would then be ascertained by reference to a table cal-
culated for the particular instrument in use, as it would depend (supposing the
adjustments to be perfect,) upon the distance between the mirrors. It may be
found advisable for some purposes where portability and promptness in obtaining
the result are not of primary importance to construct an instrument with a
distance of two or several feet between the mirrors in which case even consider-
able distances might be determined pretty accurately. Such an instrument would
doubtless facilitate the mapping of detail in a rough country across which

page_text: measurements would be difficult. In each case the distance obtained would be
the distance between the object and the mirrors, and if the object observed were
above or below the instrument the angle of elevation or depression would require
to be read and the horizontal distance would be deduced by calculation.
The improved form of Galilean telescope indicated is suited for use as a
reconnoitring telescope; for which use it is well adapted where high magnifying
power is not required.
In order that my invention may be fully understood I shall now describe and
illustrate in the drawings, the construction and details of my apparatus as shown
in a series of examples of its actual application.
The object glass may consist of any well known or other combination of lenses
suitable for the purpose and differs from those in common use only in having a
shorter focal length for a given diameter than is usual or practicable in ordinary
telescopes. This proportion depends upon the special purpose for which the
instrument is intended. For most purposes a focal length of from five to eight
diameters is suitable, but where portability is of special importance an even
shorter focal length may sometimes be used with advantage. Three typical com-
binations are represented in section in Figs. 1, 2, and 3. The portions made of
flint glass are shaded more closely than those made of crown glass, various sizes
are represented but the diameters obviously will depend on the size of the tele-
scope they are intended for.
Fig. 1 is a simple Crown and Flint combination of 1.5 inch diameter and
12.25 inches focal length.
Fig. 2 is a triple lens the diameter being 3 inches and the focal length
about 16.4. Both of these are well known forms.
Fig. 3 is also a combination of three lenses, but in this the third is separated
from the other two by an air space a. It has a diameter of 2.0 inches and a focal
length of about 6 inches.
This arrangement is suitable where a very short focus is required, and has the
advantage that it enables the adjustment for any small residual spherical aberra-
tion to be made by increasing or diminishing the air space a instead of altering
the curvature of the lens. The simultaneous elimination of chromatic aberration
of course depends upon the use of glass of suitable dispersion for all three lenses.
Referring now to the eye-piece. If only a low magnifying power, say ten to
fifteen, be desired, the telescope requires only a concave eye-piece to complete it.
The best form of eye-piece consists of two equal and similar compound concave
lenses, each corrected for chromatic and spherical aberration. These are placed
with their deep sides inwards (that is, towards each other) and spaced at a distance
about equal to the focal length of either lens but this distance may be varied
within somewhat wide limits, say to the extent of one-third of the focal length,
éither way.
This arrangement is shown in Fig. 4, each lens consists of a double concave
crown glass lens and a meniscus of flint glass but a great variety of kinds of
optical glass are now available and equivalent combinations may be made to pro-
duce the like result with such other glass by the usual methods of design.
Fig. 5 shows an eye piece of the same construction suitable for obtaining a
large field and low power. In this case the eye-lens consists of a small crown lens
of the same focal length as the field lens which answers every purpose. The
radii of two surfaces of the eye lens should be in the proportion of about 7 to 1 as
this gives least spherical aberration, the deeper side is turned towards the field
lens.
For many purposes a single lens may be substituted for each of the compound
lenses without much loss. In this case they are best made with the radii of the
two surfaces in the proportion of 7 to 1 or thereabout, and they should be spaced
as above described. Fig. 6 shews such an eye-piece.
a
When a higher power is desired the object glass may be supplemented by
concave lens corrected for two foci so placed that the shorter focus coincides with

page_text: the focus of the object glass as shown in the arrangement in Fig. 8 in which
O, is the object glass, Q, its focus. S, the supplementary lens, Q, q, its two foci.
R, the eye-lens, q, its foci.
The object glass O receives rays parallel to the axis of the instrument and
focusses them at Q.
The supplementary lens receives them before they reach Q and diverts them to
its more distant focus q. In order that it may do this satisfactorily it must be
constructed for the purpose, that is it must be corrected for both foci.
The eye-lens receives the rays and diverts them so that they leave the instru-
ment parallel to the axis. In order that it may do this its focus must coincide
with 9 the longer focus of the supplementary lens.
In the figure a single lens has been shown by way of eye-piece in order to make
the arrangement more readily intelligible.
Fig. 7 shows such a lens 0.8 diameter the shorter focus being about 3 inches
from the lens and the longer focus 10 inches, consequently the magnifying power
will be 10/3 or 31/3. If this be combined with the object glass shown in Fig. 1
whose focal-length is 12.25 we should get an image formed 19.25 inches from the
object glass of the same dimensions as would be given by an object glass of over
forty inches focus and completing the telescope by the addition of the eye-piece
shown in Fig. 5 we should have a magnifying power of about twenty-five, which
is probably as much as could be profitably used with so small an object glass.
The whole instrument would be under twenty inches in length or between 6 and 7
times the diameter of the object glass which is about half the length hitherto
usual.
Fig. 8 shews a triple lens one inch in diameter the two foci being about 3"
and 12.5" from the lens, giving a magnifying power of about 4.2. Other combi-
nations might easily be designed to effect the same thing and if the object glass
were under corrected a single lens might be used instead of the compound supple-
mentary lens and might give very good results.
When a supplemental lens is used as above described it is mounted in one tube
with the eye-piece, as the distance between it and the eye-piece would be fixed,
being determined by the focal lengths of the two, and so that the focus of the eye-
piece is made to coincide with the longer fecus of the supplemental lens.
The range finding portion of the apparatus is represented in Fig. 9 and com-
prises a reflecting prism or a plane mirror, the latter is represented in the draw-
ings and is marked b, placed in front of and covering half of the said object glass c,
and with the reflecting surface at an angle of 45° with the axis of the telescope D.
An arm or bracket not shown in the drawings fixed at right angles to the tele-
scope carries an adjustable mirror e the reflecting surface of which is parallel,
or nearly so with that of the first named mirror, and facing it, and this mirror is
mounted so as to be capable of being rotated through a small arc by the movement
of the arm f to which the mirror is rigidly attached. The arm f, has at the end
opposite to the mirror, parallel jaws y which embrace a pin h on the sector 7 near
its fixed centre j. The other end k of the sector is operated by the cylindrical
head or pinion which may be surfaced to operate the sector by friction or the two
surfaces may be finely cogged.
The head is carried by the radius bar m the pointer or vernier on which reads
on the divided quadrant n which may be divided either to give the angular rota-
tion of the mirror from which the distance may be calculated, or so that the
distance may be read off at once. In practice it would be furnished with clamp-
ing and tangent screws for accurate adjustment after being roughly adjusted by
hand.
Having now particularly described and ascertained the nature of my Invention
and in what manner the same is to be performed I declare that what I claim is :-
FE33
.

page_text: 2. The use in the construction of such telescopes of an eye-piece consisting of
two concave lenses of equal or nearly equal focal length (one or both of which may
be compound) separated by a distance about or nearly equal to the focal length of
either lens substantially as hereinbefore described.
3. The combination of a compound achromatic object glass of short focal length
with a compound eye-piece consisting of a simple or compound concave field lens
and a simple or compound eye lens separated by a space about equal to the focal
either lens substantially as herein before described.
4. The combination of an object glass such as described with a supplementary
concave lens placed between the object glass and the eye-piece in the position
hereinbefore indicated and any suitable eye-piece which may answer the purpose
for which the telescope is required.
5. In the construction of triple object glasses the use of an air-space a between
the second and third lenses by the adjustment of which spherical aberration may
be eliminated from the combination.
6. The range finding mechanism herein before described.
7. The combination with a telescope such as described of a fixed mirror or a
reflecting prism such as 6 an adjustable mirror such as e with mechanism for
rotating the same shewn in the drawings and described; a radius bar or pointer
such as m and quadrant such as n divided to show either the angular rotation of
the mirror e or the actual distance of the object viewed.
Dated the Second day of September 1897