Improvements in Photographic Cameras for Instantaneous or Time Exposures.
Year: 1894

page_text: Date of Application, 8th May, 1894
Complete Specification Left, 8th Feb., 1895-Accepted, 9th Mar., 1895
PROVISIONAL SPECIFICATION.
Improvements in Photographic Cameras for Instantaneous or Time
Exposures.
3
I ARCHIBALD GOWAN CAMPBELL of Southwell House, Southwell Gardens,
South Kensington in the County of London, Electrical Engineer do hereby
declare the nature of this invention to be as follows:-
on the
This invention relates to improvements in photographic cameras
"reflecting" principle in which the image is seen full size and can be focussed up
to the moment of exposure. In my camera only one lens is used and the mirror is
hinged and actuated by the torsion of a spiral spring or equivalent means.
The exposure begins to take place immediately the mirror commences to move
and is finished when the mirror completes its motion. The press button or
actuated part merely serves to release the mirror from its held position covering
the "sensitive" surface before the exposure, at an angle of, say, 45° to it. One
end of the axis of the mirror projects on the outside of the camera and enables
the former to be returned to its original position after the exposure has been made.
The other end in the form of a sleeve, projects on the other side and enables the
torsion of the spiral spring to be increased or diminished by rotation of the
projecting part which is connected to the abutment end of the coiled spring.
In this
Another and alternative method of regulating exposure is to attach a plunger
with piston either to the mirror and its supports inside the camera, or to a lever or
part attached to the spindle outside, with a vent hole of variable area.
case the sleeve may be dispensed with, the torsion of the spring being adjusted
once for all and the regulation effected entirely by alteration of the air vent of the
piston or chamber. Several alternative methods of attaching the shutter to the
mirror may be adopted, but one of the simplest dispenses with all additional
hinges, rollers, bearings or flexible material, and is preferably made not to touch
any part of the camera during its upward movement. This arrangement embodies
a flap rigidly fixed to the base of the mirror with an intervening slit (wide enough
to expose the whole plate at once for time exposures) the flap may but need not
necessarily be curved and such arrangement has, besides its mechanical advantages,
an important photographic one, viz. the plane of the aperture is approximately
in the plane of its motion, so that during the first part of the exposure, when that
motion is comparatively oblique to the rays of light the aperture is similarly
oblique and therefore in effect narrowed.
This is of advantage photographically as the sky should receive equal or even
less exposure than the foreground and if the angular velocity of the mirror be
constant with this arrangement the exposure of the plate will be approximately
uniform and the amount and range of "cushioning" may be adjusted so as to make
this velocity so constant.
A folding hood on the top or other part of the camera is made with an aperture
to admit the eyes and nose of the operator and of such a shape that when his face
is in position light is excluded from the ground glass or focussing screen. This
serves two purposes: 1) To enable the image to be seen distinctly in the brightest
sun light or under like trying conditions and 2) To prevent light from getting to
and through the ground glass while the mirror is moving upwards, thus rendering
it impossible to "fug" the plate thereby.

page_text: The apertures closed by the face of the operator may be provided with
magnifying lenses.
For time exposures the mirror may be held half way up by a suitable catch.
When so used I either close the hood or I provide means easily actuated for closing
the aperture in it when the face is removed.
In the latter case I have, say, a flap held by a spring against the aperture and
pushed out of the way by the bridge of the nose when the face is placed
against it.
The square or other aperture exposed by the motion of the mirror should be
large enough to admit light up to the edges of the sensitive plate even when the
lens is moved (in focussing near objects) to its farthest position from the sensitive
plate.
The lens may be moved along its axis (for focussing) by a rack and pinion or
equivalent means which may be fixed either to the lens direct or to the front of
the camera carrying the lens.
Except for portraits (time exposures) cameras are seldom required to take
vertical "hand" pictures. There is, however, no difficulty about doing so with
this instrument positioning the head and body accordingly or an ordinary "finder"
may be employed the hood being closed or a reversing frame may be used.
The plates may be changed in any suitable or convenient manner.
This arrangement of camera may be used with ordinary dark slides or roller
slide or it may be made on the magazine principle adapting the camera
accordingly.
The mirror may be mounted on metal (say aluminium) arms.
By these means the following amongst other advantages may be attained.
1. Simplicity.
2. Advantage of a double support by both face and chest, ensuring steadiness
and enabling much longer exposures to be given without shaking, than in ordinary
hand cameras.
3. Easy method of setting for time exposures with a single catch.
4. The exposure commences as the image is disappearing from the ground glass,
the exposure is finished before the mirror is stopped, thus avoiding vibration from
the change of motion.
5. The mirror may be mounted in the lightest possible way so that its motion
even when rapid is not imparted to the camera, at least until the exposure is
finished.
The mirror as it reaches the top encloses a body of air which forms a cushion
and enables rapid exposures to be made without jar or risk of breaking the glass.
This cushioning also tends to correct any tendency which the mirror may have to
accelerate its motion.
.
6. The pressure to release the catch holding the mirror is parallel to the axis of
the lens and towards the operator's body, so that the spring holding it and therefore
the mirror in its place may be made of considerable strength.
This is important because any "play" in the mirror spoils the focussing
adjustment and there is also less chance of letting it off accidentally or of its
getting out of order.
"
7. The increased facility for readily regulating the exposure.
Considerable variations may be made in the details of the arrangements without
departing from the essential features of the invention.
Dated the 8th day of May 1894

page_text: Честате une nature 01 this invention and in what manner the same is to De
performed, to be particularly described and ascertained in and by the following
statement :-
66
on the
This invention relates to improvements in photographic cameras
reflecting" principle in which the image is seen full size and can be focussed up
to the moment of exposure.
DESCRIPTION OF THE DRAWINGS.
Fig. 1 is a sectional elevation of a camera arranged according to my invention
and taken on the line C. D. of Fig. 2.
Fig. 2 is a section taken on the line A B of Fig. 1.
Fig. 3 by outline sketch shews position of user, and
Fig. 4 a much reduced sketch to shew the mode of use.
In the camera shewn only one lens is indicated (see Fig. 1) and this is marked a
in the figures. The mirror bis hinged at c and is actuated by the torsion of the
spiral spring or by equivalent means.
The exposure begins to take place almost immediately the mirror begins its
movement and is finished when the mirror has completed its motion and has arrived
at the position shewn by the dotted lines b¹.
The trigger catch e serves to release the mirror from its held position screening
the sensitive surface before the exposure. The mirror is kept in a position
which is at an angle relatively to the sensitive surface and the focussing screen gl
and it is secured in this position by the spring h. The mirror is affixed to an axis
one end of which projects on the outside of the camera and enables the mirror to
be returned to its original position after an exposure has been made. Either the
front of lens must be covered and the hood closed or its aperture filled up while
this is done, or the sensitive plate must be otherwise protected as by closing the
shutter of a dark slide. The other end projects on the other side and enables the
torsion of the spiral spring to be adjusted by rotation of the projecting part which
is connected to the abutment end of the coiled spring, or the sleeve and spindle
may both project on the same side. The knob i (Fig. 2) actuates the spiral spring
while the knob on the sleeve on the spindle c is connected with the mirror.
This spindle to which knob i is fixed rotating within the sleeve = connected with
the mirror.
An alternative method of regulating exposure is to attach a plunger with piston,
either to the mirror and its supports inside the camera, or to a lever, or part,
attached to the spindle outside, with a vent-hole of variable area.
Regulation may be effected by alteration of the air vent of the piston or
chamber when using the latter modification.
The movable part of the shutter may be connected to the mirror 6 in various
ways but one of the simplest is that shewn in Figure 1.
A flap k is rigidly fixed to the base of the mirror with an intervening slit wide
enough to expose the whole plate at once for "time exposures."
The flap need not be curved. Such flaps have photographic utility, viz.: the
plane of the aperture is approximately in the plane of motion, so that during
the first part of the exposure, when that motion is comparatively oblique to the

page_text: rays of light the aperture is similarly oblique and therefore in effect narrowed.
This is of advantage photographically as the sky should receive equal, or even less
exposure than the foreground and if the angular velocity of the mirror be constant
with this arrangement the exposure of the plate will be approximately uniform and
the amount and range of air "cushioning" may be adjusted as more fully explained
hereinafter so as to make this velocity so constant.
A folding hood m on the top or other part of the camera is made with an
aperture n to admit the eyes and nose of the operator and of such a shape that
when his face is in position, i.e. placed against the aperture, light is excluded from
the ground glass or focussing screen 9 onto which the image is reflected by the
mirror b up to the time of exposure.
This hood as shewn consists of a rigid piece of wood or other suitable material
hinged at o and having an aperture n in it.
This hood is held up when open for use by the metal hinged support p so that
the face of the operator may be pressed firmly against the parts around the aperture
and an approximately light tight joint is then made between the face and the
aperture and an extra rigid support is given to the camera.
The camera may be used with this support only, but great steadiness is attained
when a support is obtained from both face and chest, the back of the camera being
pressed against the latter.
The sides 9 of this hood are made of an opaque flexible material which folds
underneath when the hood is closed, the projecting part of the rigid piece fitting in
the spacer and the whole thus taking very little extra room.
This arrangement enables the full image to be seen distinctly with both eyes and
focussed even in bright sun-light with a small stop or under like trying conditions
and prevents light from getting to and through the focussing screen during the
upward motion of the mirror.
I have not attempted to deal with light passing round the edges of the mirror
while it is moving and thereby fogging the plate as in this camera extraneous light
never even reaches the focussing screen at that time.
The aperture closed by the face of the operator may be provided with magnifying
lenses or spectacles.
The square or other aperture t exposed by the motion of the mirror and closed
by the attached flap should be large enough to admit light up to the edges of the
sensitive plate feven when the lens is moved, (in focussing near objects) to its
farthest position from the sensitive plate. The lens a may be moved along its axis
(for focussing) by a rack u or equivalent means which may be fixed either to the
lens direct or as shewn in the figure to a sliding piece carrying the lens with a
pinion y gearing into it with its bearings in the sides of the camera and a thumb
screw projecting outside. By leaning to one side and suitably positioning the
head and body vertical pictures or pictures at right angles to their usual position
on the sensitive plate may be taken with this camera while keeping the aperture in
the hood closed by the face of the operator. Or the camera may be constructed to
take a reversing frame, or a "finder" may be used as in an ordinary hand camera,
the hood being closed. The sensitive plates may be changed in any suitable or
convenient manner the position of the sensitive plate f is merely indicated in the
figure and the back of the camera left incomplete in Fig. 1 as this portion forms no
part of my invention and ordinary dark slides or roller slide may be used or the
plates may be changed on one of the bag changing or magazine principles and the
construction of this part varied accordingly. The mirror may be mounted in a
metal frame a or on metal arms or in any other convenient way.
When used as a hand-camera for so called "instantaneous" exposures the double
support by both face and chest enables relatively slow exposures to be given
without risk of movement and ensures steadiness even when the mirror and other
moving parts within the camera are made comparatively heavy and the actuating
spring powerful.
For time exposures, after focussing and closing the hood and front of camera

page_text: or lens with the mirror down, this mirror is released and held in an intermediate
position by a catch s or its equivalent to engage the mirror frame. In this position
the aperture 1, is held opposite the lens a the exposure being made by temporarily
opening the front of the camera hinged at o', or removing part covering the front
of lens.
For time exposures a flap, spring controlled, may be used to close the sight
aperture instead of closing the hood as described.
The mirror may be mounted in the simplest and lightest possible way so that its
motion in "instantaneous" exposures is not harmfully imparted to the camera. When
however a support is given by the operator's face the lightness of the moving parts
becomes of lesser importance except with reference to the maximum rapidity of
exposure obtainable.
The mirror as it reaches the top encloses a body of air which forms a cushion
and enables rapid exposures to be made without jar or risk of breaking the glass.
This cushioning also tends to correct any tendency which the mirror may have
latterly to accelerate its motion.
The duration of "instantaneous" exposure is regulated, as indicated above by
the number of turns given to the knob which is provided with a ratchet and pawl
indicated at and may have attached any suitable indicating device to shew the
number of turns that have been given or the corresponding exposure to be
expected.
The utility of the hood shewn and described is not confined to any one particular
form of reflecting focussing camera-using this phrase in the sense hereinbefore
referred to as said hood is designed to be used with various forms of said camera
known to me.
In cases where it is not requisite to utilize the rigidity of the folding hood and
its support in aid of the support of the camera the whole or substantially the whole
of the said hood may be flexible, especially, for instance with fixed mirror and
twin lenses.
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. In a reflecting focussing photographic camera, a flexible folding hood with
aperture for the face of the operator so arranged that in use exclusion of light
from the interior is attained and if desired support to the apparatus, substantially
as set forth and shewn by the drawings.
2. A reflecting focussing photographic camera with a moving mirror and
sbutter attached thereto arranged actuated and regulated substantially as
described.
3. A reflecting focussing photographic camera capable of being supported against
face and chest of the operator, and the hood of which serves also to exclude light,
substantially as and for the purposes set forth.
4. A reflecting focussing photographic camera with moving mirror having its
focussing screen protected from light by a hood as described, which hood also serves
by being pressed against the face of the operator to steady the camera, constructed
and arranged as set forth.
5. The construction and arrangement or combination of parts of photographic
reflecting focussing camera apparatus, substantially as described and shewn by the
drawings.
WM. BROOKES & SON,
55 & 56, Chancery Lane, London, Agents for the Applicant.