Year: 1887

page_text: Date of Application, 16th May, 1887
Complete Left, 16th Feb., 1888
Complete Accepted, 16th Mar., 1888
I GEORGE DOWNING of 8 Quality Court, Chancery Lane, in the County of
Middlesex, Patent Agent, do hereby declare the nature of my said invention to be
as follows:
The object of this invention is the immediate and accurate focussing of the objects
requiring to be photographed. It is based upon a known principle which can be
easily demonstrated and which is as follows:-When an object of constant height is
placed at various distances from an object glass, there exists a constant ratio between
the angle formed by the visual rays of the operator, directed to the upper and lower
extremities of the object, and the length of the foci of the object glasses producing
at each of these distances a clear image of the same object or in other words "The
distance to which an object glass must be shifted in order to obtain upon a fixed
screen clear images of an object placed at various distances is always in the same
ratio with the angles formed by the visual rays issuing from the eye of the operator
and directed to the upper and lower extremities of the object in these different
positions. In order to measure the above mentioned visual angle I use a pair of
compasses or dividers placed above the camera the legs being caused to move with the
object glass at the time of adjustment. For this purpose the divider carries upon its
upper leg an appendage or projection from which issues a connecting rod fixed to the
other leg at an equal distance from the pivot. Another connecting rod or link
connects the first connecting rod with the upper arm of a rectangular link movable
upon an axis and whose lower arm is joined by a third rod to the movable part of the
object glass. The result of this arrangement is that if the object glass is caused to
advance or to retrogade by turning the head or knob of the rack, the compasses are
at the same time opened or closed and the angle of opening of the latter is dependent
in a determined ratio upon the movement of the object glass. A sight piece is also
077

page_text: the
fitted composed of a metal plate having a simple circular opening formed therein
arranged to coincide with the axis of the apparatus so that the vertical plane of the
opening may coincide with that of the axis of the object glass, is fixed above the
sensitive glass at a level with the dividers and enables the operator to see, between
the legs of the latter, the objects the sight of which it is desired to adjust. Under
these conditions, there remains but to regulate the apparatus that is to say to give to
the legs of the compasses or dividers and to the arms of the links suitable lengths
so that the greatest opening of the compasses may correspond with the longest focus of
the object glass, while in like manner the smallest corresponds to the smallest focus;
and also, in order that the opening of the legs of the compasses should be always
equal to the height of the images obtained upon the object glass. For this purpose
the two extreme foci of the object glass are determined by means of the unpolished
glass, the shortest or principal focus, and the longest or useful focus, that is to say,
focus producing upon the sensitive glass the largest and clearest possible image of the
object upon which it is intended to adjust the instrument. The principal focus is
obtained in the usual manner by adjusting upon the unpolished glass a very distant
object. For the longest useful focus I use an object serving as a basis for the regula-
tion, and which, for practical purposes, is ordinarily a man of medium height, or the
animal which has most frequently to be photographed; it is placed before the object
glass at a suitable distance in order to have at the same time as large and as clear
an image as possible; the places at the two foci thus obtained are marked upon the
frame or support of the apparatus, and the distance between the two is carefully
measured. The two extreme angles of opening of the compasses or dividers are
next ascertained by first closing them to the smallest angle of opening, and then, by
opening them sufficiently for the distance between its points to be equal to the height
of the greatest image of the subject clearly obtained upon the unpolished glass.
During this operation the end of the upper arm of the link is shifted, the extremities
of its stroke are ascertained, and its extent is measured. There now only remains to
calculate the respective lengths required for the legs of the compasses and the arms of
the link in order to cause the longest and the shortest focus of the object glass to
correspond with the largest and the smallest opening of the legs of the compasses,
which can be easily effected by using as a basis the means before mentioned. The
regulation is thus rendered complete, for it will be obvious that in order to adjust the
instrument for a man of medium height, whatever may be the distance at which he is
placed from the object glass, it will be sufficient to sight him through the sight piece,
by opening the legs of the compasses until their points coincide with the upper and
lower extremities of the subject, as the angles at which the operator sees the object
at the various distances are proportionate to the shifting motions of the object glass.
The above described mode of regulation may be effected with any other object, the
same compasses being used while on its legs can be fixed from distance to distance
lateral and not very prominent points acting in a similar manner to the principal
points used for the man. This instrument may be applied to any camera.
D L
1657

page_text: Improvements in the Method of Focussing the Object Glasses of
Cameras and in Apparatus therefor.
A communication from abroad by LOUIS MATHIEU BERTHON, of Vernoz (Isère), in
the Republic of France.
I, GEORGE DOWNING of 8 Quality Court Chancery Lane in the County of
Middlesex Patent Agent, do hereby declare the nature of my said invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement :-
The object of this invention is the rapid and accurate focussing of objects required
to be photographed without the use of the ground focussing glass.
My invention is based upon the well known principle, that when an object of a
certain height is placed at various distances from the object glass, there exists a
constant ratio between the angle formed by the visual rays of the operator, extending
to both the lower and upper extremities of the object, and the length of the foci of
the object glass producing at each of such distances a clear image of the same object,
or in other words, the distance to which the object glass must be moved in order to
obtain a clear image of an object placed at various distances, is always in the same
ratio with the angles formed by the visual rays drawn from the eye of the operator, to
the upper and lower extremities of the object in the different positions.
In order to measure the visual angle above mentioned, a pair of dividers are placed
above the dark chamber, the legs being made to follow the movement of the object
glass at the time of focussing.
And in order that my said invention may be particularly described and ascertained,
reference is hereby made to the accompanying drawings.
Fig. 1. shews the lens, forming the object glass in two positions.
Fig. 2. also shews the lens in two positions, with the addition of the compasses
above the lens.
Fig. 3 is an elevation of the apparatus.
Referring to Fig. 3, the compass is suspended upon a joint at A. The upper leg
is extended and the curved link B. B. is united as shewn. j is a connecting link
uniting B. B. to the arm S of the bent lever E. This lever is supported as shewn
and united to the frame or cap of the focussing lens at L. The effect of this arrange-
ment is that as the object glass is moved forward or backward by turning the ordinary
button of the pinion the compass is also caused to open or close, and the angle of
opening of the latter corresponds with the motion of the object glass. A sight piece M
consisting of a simple circular opening formed in a metal plate, is fitted over the axis
of the apparatus, in such a manner that the vertical plane of the eye piece coincides
with that of the axis of the object glass the legs of the compass pointing to the
extreme limits of the object which it is desired to focus.
The apparatus is therefore regulated by giving to the legs of the compass and to
the arms of the lever E proportionate lengths so that the largest opening of the
compass shall correspond to the longest focus of the object glass while the shortest
opening corresponds to the shortest focus in order that the distance between the points
of the compass should always correspond to the height of the image obtained upon
the sensitized plate. For this purpose the two extreme foci of the object glass are
first determined by means of the ground focussing glass, viz. its shortest focus or

page_text: main focus, and its longest focus or useful focus, that is to say that producing upon
the sensitized plate or glass the largest and the clearest possible image of the object
upon which the instrument is required to be concentrated.
The main focus is obtained in the ordinary way by focussing upon the ground glass
or focussing plate an object placed at a long distance. As regards the longest and
useful focus, the object intended to serve as a basis for the regulation is employed,
such as a man of average height or an animal which is most frequently required to
be photographed ; such object is placed in front of the object glass at a suitable
distance to receive an image as large and as clear as possible. The places of the two
foci thus obtained are marked upon the frame of the apparatus and the distance
separating one from the other is accurately measured.
The two extreme angles of opening of the compass are next ascertained, by first
closing the latter which gives its smallest angle of opening and then by opening it so
that the distance between its points are equal to the height of the largest image of the
object to be obtained with clearness upon the ground glass or focussing plate. During
this operation the extremety of the upper arm of the lever E will be shifted the
extremeties of its position being marked and the length measured. It then only
remains to calculate the respective lengths required to be given to the legs of the
compass and to the arms of the lever E in order to make the longest and the shortest
focus of the object glass correspond with the largest and the smallest opening of the
compass which is readily accomplished by making use of the two measures previously
obtained.
The regulation or adjustment of the instrument is thus completed; and it will be
understood, that in order to focus a man of ordinary size, at whatever distance ho may
be placed from the object glass or plate, it will be sufficient to sight him through the
sight piece M by moving the legs of the compass until their points coincide with the
upper and lower extremities of the object; the angles by which an operator sees an
object at the various distances being proportionate to the distances reached by the
object glass.
The method of regulation above described can be effected with other objects; the
same compass being used while upon its legs are fixed from distance to distance
lateral centres which act in the same manner whatever the object may be.
This instrument may be applied to all kind of object glasses or plates and to all
kinds of dark chambers and may be concealed therein without thereby increasing the
size of the lens. When the object piece has no rack the lever E which moves the
compass must be fixed to the moveable frame or slide of the dark chamber.
Referring to Figs. 1 and 2 A. B. is the first or initial position of the object;
A B being its image. A' B' is the second position of the same object A¹, B₁₁ being
its image.
Having now particularly described and ascertained the nature of my said Inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The method of focussing lenses and analogous apparatus by means of compasses
or dividers mounted in a line with a sight hole, and combined with means of actuating
the object glass, substantially as herein before described and illustrated on the
drawings.
2. The general combination and arrangement of the several and respective parts
together forming my improvements in the method of focussing the object glasses of
cameras and in apparatus therefor, substantially as herein before described and illustrated
on the drawings.