Improved Means and Apparatus for Securing Accurate Focus Registration in Photographic Cameras.
Year: 1893

page_text: Date of Application, 11th Sept., 1893
Complete Specification Left, 11th July, 1894-Accepted, 11th Aug., 1894
PROVISIONAL DILUITIVATION.
Improved Means and Apparatus for Securing Accurate Focus
Registration in Photographic Cameras.
I, THOMAS RUDOLPH DALLMEYER, of 25 Newman Street, Oxford Street,
London, Optician, do hereby declare the nature of the said invention to be as
follows:-
This invention relates to improved means and apparatus whereby the accurate
focussing of the object on the plane where the sensitive film is to receive the
impression can be verified without the use of the ground glass screen, in such
manner that it shall be absolutely certain that the image of the object will be
clearly registered on that plane when the sensitive film is exposed.
For this purpose I employ the following devices :-
According to one arrangement I form an opening in the top of the camera, and
near the front edge of this opening I place a mirror (preferably) in a plane parallel
to that occupied at the back of the camera by the sensitive film when the exposure
is taking place. The aforesaid mirror is enclosed in a box which covers the
opening in the top of the camera and from which box light is excluded except what
may be reflected to it after passing through the lens. An inspection opening is
made in the aforesaid covering box at a point so placed that the image of the
object registered on the focussing surface at the back of the camera is reflected to
the aforesaid mirror and thence to the eye. So that the eye looking at the said
mirror sees the reflection of the image on the focussing surface and absolutely
accurate focus registration can thereby be secured with the advantage that the
operator sees the image while facing the object itself.
The focussing surface employed may be the roller blind shutter, when such is
employed, or the back of the dark slide for example, the said surface being in
either case preferably whitened.
When the sensitized plate is normally placed or stored behind the plane occupied
by the focussing surface at the time when the focussing is effected, I arrange so
that the sensitized plate can be moved forward after the focussing has been effected
but before exposure in order that its surface may occupy exactly the position
previously occupied by the focussing surface whereby the registration of the image
on the sensitized plate is exactly the same as that on the focussing surface.
According to another arrangement, 1 place in the camera, behind the lens and
at an angle of 45° with the axis thereof, a mirror or totally reflecting prism which
reflects the rays of light passing through the lens in a direction at right angles to
such axis; these reflected rays of light are received on a second mirror or totally
reflecting prism placed in a plane parallel to the first and are reflected therefrom in
a direction parallel to the axis of the lens. The second mirror is placed at the
front end and in the axis of a telescope tube the rear or eye piece end of which is
preferably placed towards the rear end of the camera. On looking through the
telescope the reflected image of the object is seen by means of the mirrors or prisms.
In this way the lens itself becomes the object glass of the telescope and the exact
focus of the image seen through the telescope so as to coincide with that which
would be registered on the focussing surface, if there were one, or on the sensitized
plate when the latter is exposed, is effected in the following manner for each person
using the camera fitted with this arrangement.
The person who is to use the camera focusses a suitable object on the usual glass
screen by direct vision in the usual way the first above mentioned mirror being, for
the time being, moved out of the way. He then replaces the said first mirror and

page_text: focusses the telescope until he can see the reflected object therein as clearly and as
well defined as he saw the object on the glass screen by direct vision through the
lens. Whenever after that the same operator, with the same focussing of the
telescope, so focusses an object with the lens so as to bring the reflected image of
that object clearly and well defined to the eye at the telescope, he may be quite
certain that he has absolutely accurate focus registration on the sensitized plate.
The last described arrangement is more especially applicable to what is now
known as tele-photography, but it may be more or less applicable to ordinary
photography.
The first of the two mirrors mentioned in the last described arrangement is
preferably removed by suitable mechanism from behind the lens previous to and
during the exposure of the plate but instead of removing it entirely it may be
turned edgewise so that it is in a line with the axis of the lens, with its back, which
should be blackened, towards the second of the two mirrors or in some cases towards
the side of the camera. The few rays of light cut off from the plate by the mirror.
thus presented edgewise to 'the lens do not materially affect the image formed on
the plate.
Dated this 11th day of September 1893.
T. R. DALLMEYER,
Per W. H. Beck,
115, Cannon Street, London, E.C., Agent.
Improved Means and Apparatus for Securing Accurate Foous
Registration in Photographic Cameras.
I, THOMAS RUDOLPH DALLMEYER, of 25 Newman Street, Oxford Street,
London, Optician, 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, that is to say :—
This invention relates to improved means and apparatus whereby the accurate
focussing of the object on the plane where the sensitive film is to receive the
impression can be verified without the use of the ground glass screen, in such manner
that it shall be absolutely certain that the image of the object will be clearly
registered on that plane when the sensitive film is exposed.
For this purpose I employ the devices shown in the accompanying drawings.
According to one arrangement shown in Figure 1 of the drawings, which
is a diagrammatic longitudinal section of a camera, I form an opening A in the top
of the camera B, and near the front edge of this opening I place a mirror C
preferably in a plane parallel to that occupied at the back of the camera, at D, by
the sensitive film when the exposure is taking place, but the said mirror C may be
placed at any suitable angle to the plane at D. The aforesaid mirror C is enclosed
in a box E which covers the opening A in the top of the camera and from which
box light is excluded except what may be reflected to it after passing through the
lens B. An inspection opening or an eye-piece F is provided in the aforesaid
covering box E at a point so placed that the image of the object registered on the
focussing surface at the back of the camera is reflected to the aforesaid mirror C
and thence to the eye. So that the eye looking at the said mirror C through the
eye-piece F sees the reflection of the image on the focussing surface D and
absolutely accurate focus registration can thereby be secured, with the advantage
that the operator sees the image while facing the object itself.
The focussing surface D employed may be the roller blind shutter, when such is
employed, or the back of the dark slide, or a separate removable screen, or any
other suitable device the said surface being in either case preferably whitened..

page_text: When the sensitized plate is normally placed or stored behind the plane occupied
by the focussing surface D at the time when the focussing is effected I arrange so
that the sensitized plate can be moved forward after the focussing has been
effected, but before exposure, in order that its surface may occupy exactly the
position previously occupied by the focussing surface D, whereby the registration
of the image on the sensitized plate is exactly the same as that on the said
focussing surface.
According to another arrangement shown in Figure 2, which is also a
diagrammatic longitudinal section of a camera, I place in the camera B, behind
the lens B' and at an angle of 45° with the axis thereof, a mirror G or a totally
reflecting prism which reflects the rays of light passing through the lens B'₁
in a direction at right angles to such axis; these reflected rays of light are
received on a second mirror H, or totally reflecting prism, placed in a plane
parallel to the first and are reflected therefrom in a direction preferably parallel
to the axis of the lens. The second mirror is placed at the front end and in
the axis of an eye-piece I, the rear end of which is preferably placed towards
the rear end of the camera. On looking through the eye piece I the reflected
image of the object is seen by means of the mirror H or totally reflecting prism
as the case may be. In this way the lens B¹ itself becomes the object glass of
a telescope formed in conjunction with the eye piece I; and the exact focus of
the image seen through the telescope so as to coincide with that which would
be registered on the focussing surface D, if there were one, or on the sensitized
plate when the latter is exposed in the same position as the surface D, is effected
in the following manner for each person using the camera fitted with this
arrangement.
The person who is to use the camera focusses a suitable object by direct vision
on the usual ground glass screen placed with its focussing surface at D, in the
usual way, the first above mentioned mirror G being turned on its fulcrum at G¹
into the position shown in dotted lines at G³ out of the way. He then replaces the
said first mirror G into the inclined position shown in full lines and focusses with
the eye piece I until he can see the reflected object therein as clearly and as sharply
defined as be saw the object on the glass screen by direct vision through the
lens B¹. Whenever after that the same operator with the same focussing of the
eye piece I so focusses an object with the lens B' as to bring the reflected image
of that object clearly and well defined to the eye at the said eye piece, he may be
quite certain that he has absolutely accurate focus registration on the sensitized
plate at D.
If preferred the mirror H may be dispensed with and the eye-piece I placed at
the opening A and directed towards the mirror G at such an angle as will enable
the image of the object to be seen by means of the said mirror.
The last described arrangements are more especially applicable to what is now
known as tele-photography but they are also more or less applicable to ordinary
photography.
The mirror G, in the last described arrangement, is preferably removed entirely
from behind the lens B', as described, previous to and during the exposure of the
plate; but instead of removing it entirely it may be turned edgewise on an axis G³
placed in or near the axis of the camera, so that it is in a line, or nearly so, with
the axis of the lens B' as shown by the dotted circle at G. The few rays of light
cut off from the plate at D by the mirror G thus presented edgewise to the lens B¹
do not materially affect the image formed on the plate.
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 :-
First. The improved means for securing accurate focus registration in photo-
graphic cameras, which consists in the employment of mirrors, or totally reflecting
prisms, so arranged and adapted as to reflect the image of the object through an

page_text: observation opening or eye-piece, in such manner that it appears to the operator as
clearly and sharply defined as it is, or would be, on the surface of the focussing
screen, or on the sensitized plate, substantially as described.
Second. In a photographic camera the arrangement and adaptation of a mirror,
and an observation opening, or an eye-piece, whereby the image of the object
formed by the lens on a surface coincident with that of the sensitized plate when
exposed, is reflected to the eye of the operator placed at such opening or eye-piece,
substantially as described with reference to Figure 1 of the drawings.
Third. In a photographic camera the use of one or more mirrors, or of one or
more totally reflecting prisms, so arranged and adapted that the image of the
object formed by the lens is reflected to the eye of the operator through an
eye-piece in exact registration with the image that would be formed on a surface
coincident with that of the sensitized plate when exposed, substantially as described
with reference to Figure 2 of the drawings.
Dated this 11th day of June 1894
T. R. DALLMEYER,
Per W. H. Beck,
115, Cannon Street, London, Agent.
T. R. DALLMEYER,
Per W. H. Beck,
115, Cannon Street, London, Agent.