Improvements in and in connection with Photographic Cameras.
Year: 1891

page_text: Date of Application, 28th May, 1891
Complete Specification Left. 26th Feb. 1892-Accepted. 26th Mar., 1892
PROVISIONAL SPECIFICATION.
Improvements in and in connection with Photographic Cameras.
I EDMUND HAWTHORN MICKLEWOOD 5 St. Michael's Terrace Plymouth
Engineer do hereby declare the nature of this invention to be as follows:-
This invention relates to a means of exposing sensitive plates or films in a photo-
graphic camera so as to give a due ratio or balance of exposure to all parts. In a
landscape for instance, the sky, distance, and foreground, each receive a varying
time of exposure by which the best effect is produced.
To obtain this result I construct in front of the camera a dark chamber and in
the front thereof provide a rectangular opening proportional to the size of plate the
camera is adapted to take. In this opening is a rising and falling shutter actuated
and controlled by suitable mechanism.
It is desirable that the distance of the shutter from the lens should be proportional
to the focal length of same.
COMPLETE SPECIFICATION.
Improvements in and in connection with Photographic Cameras.
I, EDMUND HAWTHORN MICKLEWOOD of 5 St. Michael's Terrace, Plymouth,
in the County of Devon, 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 invention relates to a means of exposing sensitive plates or films in a camerá
so as to give a due ratio or balance of exposure to all parts of the picture; in a
landscape, for instance, the sky, distance, and foreground, each receive a varying
time of exposure by which the best effect is produced.
To obtain this result construct in front of the camera a dark chamber, and in
the front of the dark chamber provide a rectangular opening proportional to the
size of plate the camera is adapted to take.. In this opening is a rising and falling
shutter actuated and controlled by suitable mechanism.
It is desirable that the distance of the shutter from the lens should be proportional
to the focal length of same.
1 should explain that what I mean by a rising and falling shutter is any shutter
which is lifted upwards until the aperture is completely open, and after the proper
time for exposure has elapsed, is then lowered; and my reason for this arrange-
ment is, that by this means when used at a distance from the lens in a dark chamber
I am able to allow the sky in a landscape scene, for example, less exposure than
other parts of the picture." It may be ascertained by experiments, that if a shutter
works immediately over or in front of a lens in the ordinary manner, that the
picture on the sensitised plate is not obscured in proportion to the movement of the
shutter, and that with shutters as usually applied to the lens, supposing the moving
part to have passed through a small portion only of its travel, even then the whole
picture is visible on the focussing screen, whereas I have found that by interposing
the dark chamber between the lens and shutter the commencement of the raising of
the shutter causes the sensitized plate to be exposed only partially and to become
more and more exposed in accordance with the opening of the shutter, the sensitized
plate becoming in like manner gradually obscured as the shutter closes, whereby I
am able to give the sky, distance and foreground, each a varying time of exposure.

page_text: :
"
It will now be understood that by the term "rising and falling shutter" I do not
limit myself to any particular form or construction of same, but I may employ any
form or construction of shutter which will produce or act with the herein stated
effect.
In the accompanying drawings I have illustrated a camera fitted with a dark
chamber between the lens and the shutter, there being illustrated three forms of
construction of such chamber, but it should be understood that I do not limit myself
to such particular constructions or materials, as these must be varied to suit the
camera to which my improvements are to be applied..
Figure 1 is a sectional side clevation of a photographic camera provided
according to my invention with a dark chamber between the lens and a rising and
falling shutter;
Figure 2 is a plan of the front part of the camera shown at Figure 1, and
Figure 3 is a front view of the shutter opening.
The dark chamber is formed by a front plate A, between which and the sliding or
removable plate G to which the lens Ę is fixed, there is a bellows D; the front
plate A is supported by suitable supports, so that it may be adjusted as to distance
from the lens; I have shown for this purpose a metal piece B passing under the
base C of the camera and fixed in position by a set screw B, although other supports
may be employed according to circumstances.
In the front plate A there is an aperture covered by a rising and falling shutter F,
the latter being operated in any convenient manner, there being numerous well-
known devices for operating such photographic shutters; in Figure 2 at H is
indicated a device for actuating the shutter by pneumatic pressure, but as there is
no special novelty in such arrangement, it is unnecessary for the purposes of this
Specification to further describe same; the front view Fig. 3 shows the shutter F
and a portion of the lever FI for raising and lowering same. When necessary the
lens may be removed or replaced through the shutter opening, and by unscrewing
the set screw B₁ the front dark chamber may be removed with the sliding plate
carrying the lens.
The foregoing construction may be varied to suit other descriptions of cameras,
thus at Fig. 4 the dark chamber is built out from the camera, the sides D and
front A being formed solid, and such a construction may be employed for "hand
cameras, or the dark chamber according to my invention may be formed, as, is
shown at Fig. 5, where on the top and side of the front plate A there are pins A',
onto which a cloth D is secured, which falling round the camera thereby forms the
dark chamber between the lens E and the front plate A.
It is a well known principle in optics that the rays passing through the centre of
a lens form by far the most perfect image when focussed and thrown on any surface
to receive them, hence the use of diaphragms to cut off the outside "pencils" and
use only or principally those passing centrally.
From this as a starting point and as the result of observation and experiment, I
have discovered that shutters acting in close juxtaposition to the lens act as inferior
shaped diaphragms causing the worst part of the lens, viz. the edges, to do the work
during a large proportion of their action, as when a lens is only partially uncovered
from the edge, the image is being formed and transmitted by the marginal portion
only.
Diaphragm shutters working centrally are free from this defect, but as they
expose the plate evenly they fail to give a due balance of exposure as required for
the best results to the several parts of the landscape.
Again, the image transmitted by a lens is at all times a circular one, of which in
photographic cameras a rectangular portion taken centrally only is used, and with
cameras as usally constructed the remainder is thrown on the top, sides, and bottom
of the camera, so introducing light into the camera not used in the formation of the
image, and which with the exceedingly sensitive plates now,used degrades the
.image.
In the new combination of dark chamber and shutter in front of the lens, now

page_text: introduced, all these defects are obviated, as the former frames the view in front of
the lens and so only allows light actually falling on the sensitive plate to pass into
the camera, and the shutter being applied to the front of this chamber, at a
distance from the lens, in no way interferes with the full and efficient action of the
latter.
:
A suitable proportion for the rectangular opening provided in front of the dark
chamber and in which the shutter works, I have found to be half the linear
dimensions of the plate the camera is adapted for the rectangular opening is
adjusted to or situated at such a distance in front of the lens that only the view
actually falling on the plate is transmitted, and all side-light is cut off, thus with
long focus lenses it will be evident that the shutter aperture should be placed
further away, and with shorter focus lenses, brought closer.
The shutter being placed at a distance from the lens, the latter photographs the
movements of the shutter, hence as the said shutter moves up and down, the sensitive
plate is exposed as if by a rolling curtain which starts from the foreground and
returns to the same, the result being that the most delicate cloud effects existing
are secured, together with a fully exposed landscape, in a manner far superior to
that hitherto obtained.
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 I am
aware that it has been heretofore proposed to employ a shade outside the lens of a
camera to cut off extraneous light, and I am also aware that a dark chamber has
been proposed to be employed in front of a photographic lens. Photographic
shutters which have a lifting or rising and falling motion are not in themselves
new, I therefore lay no claim to these parts taken alone or separately but what I do
claim is :-
1. In photographic cameras, the combination with a lens and a rising and falling
shutter, of a dark chamber arranged between the lens and the shutter, whereby
sensitive plates or films are exposed so as to give a due ratio or balance of exposure
to all parts of the plate or film, and to exclude all extraneous light, all substantially
as herein set forth.
2. The general arrangement and construction of photographic cameras substan-
tially as shown on the accompanying drawings, the prominent feature being, the
combination of a dark chamber arranged between the lens and a rising and falling
shutter as set forth.
Dated this 26th day of February 1892.