A NEW OR IMPROVED CHRONOMETRIC OBTURATOR FOR USE IN PHOTOGRAPHY
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Edward Griffith Brewer at the
Office of the Commissioners of Patents on the 3rd November 1881. A com-
munication from abroad by Paul Boca, of Paris, France.
EDWARD GRIFFITH BREWER, of 33, Chancery Lane, in the County of Middlesex.
"A NEW OR IMPROVED CHRONOMETRIC OBTURATOR FOR USE IN PHOTOGRAPHY."
(A communication from abroad by Paul Boca, of Paris, France.)
The rapid impressionability of photographic productions recently discovered
obliges the operator to know to the smallest fraction of a second the time of the
sitting, and to be able to accurately measure its duration so as to reproduce the
same effects each time that he operates under the same conditions of light.
The obturator which is about to be described automatically produces this
measurement and the action of the opening and closing of the object glass or lens.
A needle being placed on the division of a dial which indicates the duration of the
sitting, it is only necessary to press on a detent for a first shutter to open a passage
to the light, and a second shutter closes this passage after the period of exposure
required has taken place. This period may vary fraction by fraction from the
hundredth part of a second to three, four, five seconds, and more if required.
The board or frame which carries the apparatus is fitted on to the dark chamber,
there is a box which contains the opening and closing shutters, and a tube to which
the lens or object glass is screwed; the opening shutter is pivoted on the same
centre as its button, the closing shutter is pivoted on the same symmetrical centre
as its button; there is provided a spring for opening the opening shutter, and another
spring for closing the closing shutter. There is a dial plate divided as may be
desired, generally into 150 divisions, each representing the fiftieth of a second, and
a needle moved by the hand through the button, the point of which indicates the
time of sitting required. A chronometer ineasures the time of sitting, and will be
hereafter described more fully; a detent regulates the departure or time of opening
of the shutter, either operated by the finger or by an india rubber bag, in which
case the pressure of air will pass by a tube and disengage the catch; the shutter is
held by an arm until the closing of same by abutting on lever; an arm holds the
opening shutter up to the moment of the opening of same by abutting on a
projecting part of the catch.

page_text: When the needle is turned by the hand to the right, a ratchet is moved two
teeth, at the same time a watch spring is set which is contained in a channel
concentric with this ratchet, and made in plate. If the needle is let go a wheel
pushes the escape wheel which acts on the anchor. The governing action of this
anchor enables the motion to be regulated by adjusting on the same axis a disc,
more or less heavy according to the speed to be obtained. The number of the teeth
of the wheels and pinion are so calculated in order that the anchor makes from
one hundred to one hundred and fifty vibrations per second according to cir-
cumstances; thus, in the case where one turn of the face is made in three seconds,
the numbers are 84, 18 for the wheels and 7 for the pinion.
This combination thus arranged acts in the following manner:-The catch is
lowered by the outside arm which stops the movement of the chronometer by the
pins; the arm is placed in the upper end of the detent to keep the opening shutter
closed; the time to be occupied for the setting is marked by the needle by turning
it to the right; the right arm is hooked on the edge of the lever which projects
to the exterior of the box; at the desired moment the india-rubber is acted on or
the detent is pressed, when the following action takes place:-Under the detent
there is a sheet of india-rubber which raises this detent. This detent being raised
leaves under it the catch. The chronometer is free, the shutter being liberated
_also_falls, the opening-of-the-object-glass-or-lens-takes-place; the chronometer
having arrived at zero acts by the means before indicated on the lever, which
disengages the arm carrier of the closing shutter, and this closed, the operation is
finished.
The arrangement of the chronometer has the advantage as will be seen that it
is wound by the action even of setting the needle. The rapid vibration escapement
allows the movement to acquire from it the first movement, the speed which it will
have throughout its course.
The face is generally divided into 3 seconds, itself being divided by 50, and thus
the dial is divided into 150. In certain apparatus if the movement of the needle
is found to be too short the course may be doubled; for this purpose a pin passes
through the centre axis abuts on a second pin fixed to a disc which carries a
finger piece; this finger piece is intended to act on the lever when the needle
arrives at zero. Thus, if the axis is turned to the right this axis can make a
3/4 turn before meeting any obstacle in the other direction, even three turns can be
made with a second disc. Greater movements may be made in the following
manner: On the escape pinion a second wheel is rivetted which has forty teeth
instead of eighteen, and an anchor of smaller size is arranged at the side of the
anchor described. By an engaging mechanism, which it is not necessary to
describe, one of the two escapements is engaged, and the speed may thus be varied
so as to make the turn of the dial by the needle in twelve, fifteen, or twenty
seconds, or in three seconds, according to the engaging escapement. Any other
escapement accomplishing the same object may be used, but it is important that it
be a clock movement which takes immediately the speed which it would have
throughout its course.
It should be noticed that to prevent concussion at the opening the shutter falls
on a spring which breaks the blow.
The saine mechanism with a double action of the lever may be made to close
through the centre of the object glass or lens by means of two opening shutters
and two closing shutters, whether semi circular or of cross form.