Improvements in and connected with Shutters, Caps, or Coverings for Lenses of Photographic Instruments.
Year: 1894

page_text: Date of Application, 12th June, 1894-Accepted, 25th Aug.. 1894
COMPLETE SPECIFICATION.
Improvements in and connected with Shutters, Caps, or Coverings
for Lenses of Photographic Instruments.
1, HENRY THIEBEAULD-DE LA CROUÉE of Homeleigh, Whitehall Road,
Woodford, Essex, Gentleman, do hereby declare the nature of this invention and
n what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
The object of my invention for improvements in and connected with shutters,
to improve the con-
caps, or coverings for lenses of photographic instruments
struction and operation of the same, so as to expose a part of the area of the lens
and also the part corresponding therewith on a sensitized plate for a longer or
shorter period as may be desired, so as to govern the central and side powers of
the lens equally, or if necessary unequally, on the picture plane, and allow varied
periods of exposure on different parts of the sensitized plate. With this object I
provide a circular disc fitted concentrically and entirely covering the lens with a
small aperture therein of a suitable form to equalize, graduate, or vary, the central
and side and other powers of the lens and to stop out the centre or as desired any
other part of the lens with reference to reception, detail and distribution of light
and give a longer or shorter period of exposure to any part of the sensitized plate
through an aperture the area of which increases from the centre of the disc towards
the periphery and vice versa, the lens never being entirely exposed at any given
time.
When desiring to give greater exposure to the edges of the sensitized plate the
aperture is triangular in form with a circular base, the apex being at the centre
and the base at the periphery whilst the reverse is the case if the centre is to
receive the greater exposure.
The disc is mounted in a suitable shutter-frame and made capable of revolution.
a fixed
It also acts in conjunction with a cover or drop shutter turning on
pivot on the shutter-frame in order to close the exposed aperture in the disc
before the commencement and at the finish of one or more of its revolutions.
My invention will be readily understood by the following description having
reference to the accompanying drawings,
Figure 1 being a front elevation showing the appliance for controlling the time,
manner and degree of exposure of the plate, the shutter being shown in its closed
position.
Figure 2 is a similar view showing the appliauce as in action, a portion of the
shutter frame having been removed to show the mounting of the circular disc,
and.
Figure 3 is a vertical section on the line X Y of Figure 2.
Figure 4 is a view of the disc detached, and Figure 5 is a view of the disc frame
detached.
A is the shutter-frame formed with an aperture A' as at Figs. 3 and 5 and
adjustable to the lens of the camera, B is the circular disc, Figure 4 having the
aperture B therein, its edge taking into a rabbet formed around the aperture A¹ of
the frame A. CCCC are peripheral bearing wheels to keep in position the
disc B, the latter being grooved on its periphery and fitted with a cord D, the ends
of which are guided by pulleys and guides D' D* Figures 1, 2 and 3; the disc is
E is the cover
retained in its rabbet by means of the frame parts A Figure 1.
pivotted at E' on the frame, and normally held in a closed position (Figure 1) by
a spring such as E³ against stop pins or fingers E³ on the disc. F is a cam pro-
jecting from the disc B to support the cover E whilst in its raised position as in

page_text: Figure 2 during the revolution of the disc B. G is a cord passing over a suitable
guide and fixed to the cover E whereby the said cover may be raised in order to
-reverse the motion of the disc B so as to set the apparatus previous to using the
same, or the cord may be dispensed with.
When a plate is to be exposed the cord is pulled in the direction of the arrows
Fig. 2, the upper stop pin or finger E³ (Fig. 1) acts on and raises the cover E into
the position in Fig. 2, the disc B continuing to revolve, the cover E being held up
by the cam projection F until the revolution is completed when the cover E drops
again into the position at Fig. 1.
When desired a spring-actuated barrel, or the like, may be employed to effect
the revolution of the disc B, instead of the cord as shown, and the cover E
may be arranged to drop by gravity and the spring E' dispensed with.
I do not limit myself to the triangular shape of the aperture B₁ as an approxi-
mation thereto where the aperture is increased in width or area from the centre
towards the circumference of the disc B will effect the purpose, and when it is
desired to give greater exposure to the centre and lessen the exposure of the sides
of the plate, the direction of increased width or arca would be reversed.
By my invention I am enabled
1. To equalize, graduate and vary the central and side and other powers of the
lens and to stop out the centre or as desired any other part of the lens with
reference to reception, detail and distribution of light.
II. To produce a photograph by exposing only a portion of the lens at a time
and to effect the partial exposure by circular motion.
III. To give longer or shorter exposure to any part of the lens at any given
time.
IV. To reduce halation.
V. To give more detail than with the open lens without corresponding diminution
of light or increase of period of exposure.
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. A revolvable circular disc arranged concentrically in front of the lenses of
photographic instruments and formed with an aperture decreasing in width or area
from the circumference to and beyond the centre thereof, or vice versa, in com-
bination with a cover adapted to automatically open and close the disc aperture at
the commencement and finish of one or more revolutions of the disc, substantially
as set forth.
2. In photographic shutters, the revolvable circular disc B with aperture B¹
arranged concentrically in front of the camera lens, suitable framework A and A*,
and rollers C to carry the disc B, and means for revolving the disc, in combination
with a cover such as E co-acting with a supporting ring F on the disc B to retain
the cover E raised while the disc is revolving, with starting and stop pins or
fingers E E, all substantially as set forth.
Dated this 11th day of June 1894.
H. THIEBEAULD DE LA CROUÉE.