Improvements in Photographic Lens Shutters.
Year: 1890

page_text: ate of Application, 20th Feb., 1890-Accepted, 29th Mar., 1890
COMPLETE SPECIFICATION.
Improvements in Photographic Lens Shutters.
I FRANK BISHOP, of the firm of Marion & Co., 22 and 23 Sobo Square in the
County of Middlesex, Dealers in Photographic Materials do hereby declare the nature
of this invention (a communication to me from abroad by the firm of Voigtländer
and Son, of Brunswick, Germany) 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 an improved photographic lens shutter (particularly
adapted for the "Voigtlander" lens) which is designed to operate in such manner as
to admit and cut-off the luminous rays as nearly simultaneously over the whole
aperture of the lens as is practically possible.
In shutters heretofore made, the uncovering of the lens proceeds either wholly from
the margin to the centre or, less frequently, from the centre to the margin, whereas,
for optical reasons, the uncovering and covering of the lens should, theoretically, be
simultaneous over the whole area of the lens.
In order to approximately accomplish this result, the improved shutter of this
invention is somewhat similar in principle to the well-known "Iris” diaphragm,
except that the laminæ or sections of which the shutter proper is composed are of a
peculiar form, fewer in number, differently pivoted, and overlap each other in such a
way as, when in the closed position, to totally close the lens aperture, and, when in
the partly open position, to admit light, not only at the centre but in ray-like
apertures extending towards the margin.
It is to the peculiar form and operation of the lamina or segments that the
approximately simultaneous opening and closing of the lens is due. They are so
combined with actuating mechanism that they may be caused to pass from the closed,
to the fully-open, and back to the closed, position at any desired rate of speed,
according as an "instantaneous," or prolonged, exposure is required.
The Invention will be described with reference to the accompanying drawings,
forming part of this specification, wherein figure 1, is a front elevation of the shutter
closed and "set" for an exposure, part of the frame or casing being broken away to
shew the form and mode of operating the segments. Figure 2 shews a rear view of
the shutter, corresponding to figure 1. Figure 3 shews the shutter partly open.
Figure 4 is a rear view of the setting and releasing mechanism shewn in figure 1.
Figure 5 is a detail. The same letters of reference indicate like parts in all the
figures.
The shutter is constructed of four thin steel segments or plates a, of the peculiar
form shewn in figure 1, pivoted on centres 6 at equal distances apart around the lens
tube, the said pivots and segments being mounted in a hollow annular frame A. The
tail ends of the several segments are connected, each by a pin and slot connection c,
to a surrounding ring d, contained within frame A, by the partial rotation of which
ring the plates are oscillated on their pivots b.
The annular frame A is of such breadth as to wholly receive the plates a within it
when the shutter is fully open so as to leave the aperture quite clear. The plates a
are in slightly different planes so that when in the closed position the end 1 of each
segment will overlap the adjacent inner edge 2 of the next segment and the inner
corners of all four segments will overlap each other at the centre. The edge 2 of
each segment is curved to the radius of the full- aperture of the lens (with the
circumference of which it coincides when the shutter is fully-open) whilst the
curvature and amount of overlap of the end 1 of the adjacent segment is such, that,
concurrently or nearly so with the opening of the shutter at the centre, ray-like
openings a proceeding from the centre towards the margin will be formed by the
separation of the edges 1 and 2 of adjacent segments, as shewn in figure 3, whereby
the whole area of the lens will be at once flooded-with light.

page_text: The
The ring d is rotated to and fro, through an arc of sufficient amplitude to bring the
segments from the closed, to the fully-open, and back to the closed, position, by a
crank pine on a spring-barrel f, the crank pin being connected by a link g with a
lever arm on a shaft mounted in casing A and which also forms the pivotal axis 6 of
one of the segments a, the relative normal position of the parts being such that the
crank pin (which makes about half a revolution) is at a dead point when at its mid-
position and the shutter is fully-open so that by the complete motion of the crank pin
the ring d will be moved first in one direction and then back again sufficiently to fully
open, and then close, the shutter. The revolution of the barrel f is limited by a
stop between shoulders of a mutilated disc j fixed to the spring barrel; k is a
handle by which the barrel is turned to the "set" position for exposure.
disc has two shoulders ; and that abut against a shoulder 1 on a detent
lever 1, the shoulder ¹ corresponding to the "set" position, and the shoulder
to the fully-open position, of the shutter. The detent is pressed by a spring 12
into position of engagement with the disc ; and is disengaged therefrom by a
trigger lever m, of the peculiar construction shewn in figure 4. It is pivoted
at m' and is actuated by the ordinary pneumatic contrivance P, its motion being
limited by a stop m². It acts on the free end of the detent through the medium
of an adjustable escapement piece n pivoted at n¹ to the back of lever m and
adjusted thereon in either of two positions by means of an eccentric or cam o
adjusted by a finger lever p and against which the piece n is pressed by a
spring n².
In the one position, shewn in figures 1 and 4, the escapement piece n
holds the detent / free of the discj so long as the lever m is held by the pneumatic
contrivance against stop m² and such would be the action for an "instantaneous
exposure or for an exposure of a few seconds under the control of the brake to be
presently described. But, for a more prolonged exposure, the piece n would be
adjusted by lever p through cam o, as seen in dotted lines in figure 4, so that
(after moving the detent 1 out of engagement with the shoulder ¹ of disc ;) the
detent would escape past piece n to its normal position, so that its shoulder A,
after being moved out of engagement with shoulder, will be immediately
brought into the path of the shoulder and so arrest the spring-barrel in its mid-
position, even when turning at its greatest speed. The shutter will thereby be held
fully-open for any desired length of time and may then be closed by again raising
lever m to disengage the detent from shoulder j³.
"
The escapement piece n is returned to operative position, with regard to detent ?,
after operating on it for the first time as above mentioned, by the spring n' which
allows the piece n to yield and pass the end of the detent during the return movement
of the lever m.
99 are a pair of spring clips embracing a boss on the barrel and
pressed together by a clamping screw r whose head has a micrometer index so that it
is capable of fine adjustment. When the screw is set at zero, the brake has no action
on the barrel, but it may be adjusted so as to prolong the exposure for definite periods
up to about six seconds during which it is necessary to keep the lever m raised so as
to hold the detent free of the disc j.
The shutter is intended to be mounted between the lenses of a double combination,
immediately in front or rear of the diaphragm which is inserted in the usual guides s
between the plate t and the outer plate of the casing A.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, 1 declare that what I
claim is :-
1. In a photographic lens shutter composed of segments or plates pivoted to an
annular frame and simultaneously moved about their pivots, the construction of the
said plates of such form as to open or separate from each other at the centre and at
practically the same instant or immediately afterwards, in the direction of the
circumference in the form of curvilinear ray-like extensions of the central aperture,
substantially as specified.
2. The combination, with the herein-described shutter and its spring-actuated crank

page_text: motion provided with a shouldered disc, of the spring-actuated detent adapted to
engage with either shoulder of the said disc and arrest the shutter in either of two
positions, as, and for the purpose, specified.
3. The combination, with the herein-described shutter and its spring-actuated crank
motion, of the spring-actuated detent adapted to engage with the spring motor and
arrest the shutter in either of two positions, and of the trigger lever provided with an
adjustable escapement piece adapted to act on the detent and disengage it from the
spring motor with whichever shoulder it may be in engagement, and capable of being
so set as to keep the detent out of engagement with the spring motor during the
whole motion of the shutter or allow the detent to immediately fall back into engage-
ment with the spring motor so as to arrest the shutter when it reaches the fully-open
position, as specified.
4. In the herein-described shutter-actuating and releasing mechanism, the combina-
tion, with the trigger and escapement piece, of the cam or eccentric for adjusting said
escapement piece in either of its two positions, as specified.
F. BISHOP.
By A. M. & Wm. Clark,
53, Chancery Lane, London, Patent Agents.