Improvements in Sighting Devices or Picture Finders for Cameras or other Instruments.
Year: 1894

page_text: Date of Application, 8th May, 1894
Complete Specification Left, 8th Feb., 1895-Accepted, 9th Mar., 1895
PROVISIONAL SPECIFICATION.
Improvements in Sighting Devices or Picture Finders for Cameras
or other Instruments.
I, JEAN BAPTISTE WEBER of 95 Boulevard Beaumarchais Paris in the
Republic of France, do hereby declare the nature of this invention to be
as follows:
In photography, sighters or picture finders are designed to enable the operator
to see, before reproduction on the sensitive plate, a reduction of the image or object
which will be impressed on the finished plate. The appearance of the picture shows
the operator how he must place his camera.
The clearer and more accurate the reduced image, the more valuable the service
rendered by the sighter or picture finder, by reason of the increased facility of
procuring the most suitable aspect and selecting the point of view which will
result in the production of the most harmonious and artistic negative.
The sighter or picture finder which will yield the best results in this respect
is that in which the image will be presented to view exactly as it appears
naturally, i.e. in a right aspect and in its true proportions, without inversion or
distortion.
It is to obtain this result that I have invented the sighter or picture finder which
forms the subject of this application.
This device is essentially constituted by two mirrors or polished surfaces
reflecting the image in full daylight and comprises two parts joined by a hinge
and of which one is attached to the camera by any suitable fitting such for instance
as a slide. A mirror is placed on the bottom of this fixed piece. The movable
part carries a diminishing mirror hereinafter referred to as the movable mirror
with a suitable convex reflecting surface, the dimensions and radius of curvature of
which are proportioned to the field of the object-glass.
The image given by the movable mirror would be reversed laterally if regarded
directly. The fixed mirror which has a coucave reflecting surface, is intended to
correct that reversion and magnify the diminished picture. This fixed mirror may
also, if necessary, have a plane reflecting surface; but 1 have found it more
advantageous to use a slightly concave mirror, for the purpose of slightly
enlarging the picture and in a certain degree compensating for any slight distortion
produced by the convex or movable mirror.
These two mirrors may consist either of metallic reflectors, or plates of glass
having one of their surfaces covered with a metallic film or a coat of black or very
dark varnish.
The relative positions of the two mirrors depends upon the angle at which the
right image must be directed to meet the eye of the operator. When the visual
ray is nearly perpendicular to the fixed mirror which is in general the case of most
frequent occurrence, the most favourable position for the movable mirror is that in
which its plane forms an angle of about 30° with the vertical plane behind it,
(passing through the hinge); it would therefore be inclined forwards, towards the
ground. The fixed mirror will then be placed slightly in advance of the vertical
plane above-mentioned, and inclined forwards and upwards at an angle of from 5°
to 10° with the horizontal plane.

page_text: According to my experience the following construction and arrangement of mirrors
are the most advantageous. The movable mirror is made of a plano-concave lens,
having its concave surface silvered, so as to make a convex reflector whereof the
radius is equal to about 10 or 12 centimetres. The fixed mirror is also glass and
plano-concave, its radius of curvature being from 18 to 20 centimetres, or even
more. This glass may be dark-coloured or, if transparent its plane surface is
covered with a coat of black varnish, so that the concave surface may become the
reflector. The mirrors may be permanently fixed upon the camera, or placed on a
suitable stand in a box opening sufficiently to permit of the double reflection of
the image.
2
For the purpose of limiting the opening of the box, a slotted bar in which a small
stud fixed to the movable part slides to and fro is jointed on a pivot secured to the
fixed part. A stop behind the hinge may also be used, in lieu of the slot and stud,
to limit the opening of the box.
It is to be understood that I reserve to myself the right to substitute for the said
stop, or slot and stud any other mechanical equivalent effecting the same object,
such as a spring, a blade with catch etc.
In order to facilitate the adjustment of the picture to the sensitised plate, lines,
vertical, horizontal or oblique may be drawn upon the movable mirror. If the
latter is square and carries diagonal lines the operator will be enabled easily and
quickly to decide by an inspection of the reflected image, when formed, whether
it would be better for him to take it with the plate horizontal or vertical.
A sighter or picture finder made to be used with a camera of given dimensions
may also be used with cameras of smaller size. It would suffice to place in front of
the movable mirror and there to secure it by any convenient means such as tourni-
quets or buttons, a blackened frame intermediately superimposed, leaving open in
the centre of the mirror only the necessary opening corresponding to the smaller
sized plate.
There may be several such frames with different openings in
series, and placed in a groove or slide made by saw-cuts in the cover of the
sighter or picture finder.
If, for example, in a sighter made for photographic plates 18 x 24 the radius of
curvature of the movable mirror is calculated to give the necessary field with a
mirror of which the side is 44 millimetres, then a blackened frame of the same
external dimensions and having a square central opening of which the side is
from 36 to 38 millimetres, will be applied to the mirror, when the plates to be
used are 13 × 18. The opening will be only 30 or 32 millimetres square for
9 × 12 plates.
For other kinds of plates, the dimensions of the side of the interior square, which
will give the necessary field, may easily be calculated.
In order to guide the operator in determining whether to place the plate for a
vertical or for a horizontal picture the stop-frame may have small squares or angles
with a side of from 3 to 4 millimetres, fitted into the corners.
I reserve to myself the right of adapting my improved sighter or picture finder
for use not only with all kinds of cameras, but also with all optical instruments, and
other instruments of precision, whereof the employment may be facilitated by my
invention.
Dated this 8th day of May 1894.
W. P. THOMPSON & BOULT,
Agents for the Applicant.

page_text: Improvements in Sighting Devices or Picture Finders for Cameras
or other Instruments.
I, JEAN BAPTISTE WEBER of 95 Boulevard Beaumarchais, Paris in the
Republic of France, 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 :-
In photography, sighters or picture finders are designed to enable the operator
to see, before re-production on the sensitive plate, a reduction of the image or object
which will be impressed on the finished plate. The appearance of the picture shows
the operator how he must place his camera.
The clearer and more accurate the reduced image, the more valuable the service
rendered by the sighter or picture finder by reason of the increased facility of
procuring the most suitable aspect and selecting the point of view which will result
in the production of the most harmonious and artistic negative.
The sighter or picture finder which will yield the best results in this respect
is that in which the image will be presented to view exactly as it appears
naturally, ie. in a right aspect and in its true proportions without inversion or
distortion.
It is to obtain this result that I have invented the sighter or picture finder which
gives a rectified image in all directions and forms the subject of this application,
and is illustrated by way of example, in the accompanying drawings.
This device is essentially constituted by two mirrors or polished surfaces
reflecting the image in full daylight.
Figure 1 represents any sighter fixed upon any camera;
Figure 2 is a perspective view of the device when open;
Figure 3 represents a longitudinal section of the same;
Figure 4 is a transverse section of the sighter when closed.
The sighter comprises two parts A and B joined by a hinge C and of which one
part A is attached to the camera by any suitable fitting such for instance as a
slide D. A mirror E is placed in the bottom of this fixed piece A. The movable
part B carries a diminishing mirror F hereinafter referred to as the movable mirror,
with a suitable convex reflecting surface, the dimensions and radius of curvature of
which are proportioned to the field of the object glass.
The image given by the movable mirror F would be reversed laterally if regarded
directly. The fixed mirror E which has a concave reflecting surface is intended to
correct that reversion and magnify the diminished picture. This fixed mirror E
may if necessary have a plane reflecting surface; but I have found it more
advantageous to use a slightly concave mirror, for the purpose of slightly enlarging
the picture and in a certain degree compensating for any slight distortion produced
by the movable mirror F.
These two mirrors may consist either of metallic reflectors or plates of glass
having one of their surfaces covered with a metallic film or a coat of black or very
dark varnish.
The movable mirror F is made of a white or feebly-coloured plano-concave lens,
having its concave surfaces silvered so as to make a convex reflector whereof the
radius is equal to about 10 or 12 centimetres. The fixed mirror E is also glass and
plano-concave. This glass may be dark-coloured or if transparent its plane surface
is covered with a coat of black varnish, so that the concave surface may become the
reflector. The mirrors may be permanently fixed upon the camera, or placed on a
suitable stand in a box opening sufficiently to permit of the double reflection of the
image.

page_text: For the purpose of limiting the opening of the box, the rear edge of the part A
is bevelled so as to serve as a stop to the part B. A stud H placed on the latter,
when the device is open engages with and is retained by a spring G on the part A
so as to maintain the mirrors in one constant relative position.
It is to be understood that I reserve to myself the right to substitute for this
arrangement of spring and stud (quite a subordinate one) any other mechanical
equivalent effecting the same object.
In order to facilitate the adjustment of the picture to the sensitised plate, lines,
vertical horizontal or oblique may be drawn upon the movable mirror F.
I reserve to myself the right of adapting my improved sighter or picture finder
for use not only with all kinds of cameras but also with all optical instruments,
and other instruments of precision, whereof the employment may be facilitated by
my invention.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what I
claim is ;-
1. A sighter or picture finder characterised by the combination of two mirrors
having spherical reflecting surfaces (that of the mirror wherein the operator secs
the image or picture being alternatively plane if desired) the said mirrors being
adjustable in such manner as to give by double reflection a right or rectified image
of the object substantially as described.
2. A sighter or picture finder of the kind claimed in Claim 1 provided with
means for facilitating the adjustment of the mirrors to a suitable angle with one
another and for their maintenance at that angle substantially as and for the purpose
described.
3. A sighter or picture finder substantially as and for the purpose herein before
described and illustrated in the accompanying drawings.
Dated this 8th day of February 1895.
W. P. THOMPSON & BOULT,
Agents for the Applicant.