Measuring the Speed or Time of Exposure of Photographic Instantaneous Shutters.
Year: 1888

page_text: Date of Application, 18th Apr., 1888
Complete Specification Left, 18th Jan., 1889
Complete Specification Accepted, 23rd Feb., 1889
Measuring the Speed or Time of Exposure of Photographic
Instantaneous Shutters.
I, WILLIAM JOHN WILSON of No. 1 Chapel Road, Ealing, Middlesex, Chemist do
hereby declare the nature of this invention to be as follows:-
To carry out my invention I use a sheet of glass or other transparent or translucent
material, upon which are marked one hundred or other convenient number of dots,
lines or other divisional marks arranged in a circle and at equal distances apart―This
plate marked with the graduated circle may be made of translucent material, the
divisional marks being opaque as above described, or the plate may be opaque and the
divisional marks translucent-For instance, in the latter case the plate may be made
of metal and the divisional marks holes through which light can pass-The graduated
circle plate being fixed in an upright position an opaque circular disk a little larger
than the graduated circle is placed parallel and very close to and concentric with the
graduated circle-The opaque disk is perforated with a radial slot, the width of which
is the same as that of one division on the graduated circle, and the disk is arranged so
that it may be caused to revolve on its centre at any required speed. It will now be
understood that if the graduated circle plate be illuminated from the back and the disk
be caused to slowly revolve the divisions on circle will become visible one at a time
and in succession, to an observer standing in front of the revolving disk-In order
to measure the speed of a shutter I set the disk in motion and keep it revolving at a
uniform rate say for example once in each second-1 strongly illuminate the
graduated circle plate from behind with sunlight, electric light, the light of burning
magnesium or other sufficiently powerful illuminant, and then using the shutter to
be tested with a lens and camera in the usual way, I photograph as much of the
graduated circle as becomes visible through the revolving slot during the action of the
shutter. If the time of revolution of the disk is greater than the time of exposure of
the shutter, the latter is shown by the number of divisions which appear in the
resulting photograph-For example if the circle be divided into one hundred parts
and the disk be revolving at the rate of twice per second and twenty five divisions
appear in the photograph, then the time of exposure of the shutter is evidently
or eigth of a second.
Dated this 17th day of Anvil 1000
th

page_text: Measuring the Speed or Time of Exposure of Photographic
Instantaneous Shutters.
I, WILLIAM JOHN WILSON of No. 1 Chapel Road, Ealing, Middlesex, Chemist 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:
My invention relates to a method of measuring the speed or time of exposure of
photographic instantaneous shutters.
To carry out my invention I use a sheet of glass or other transparent or translucent
material upon which is marked one hundred or other convenient number of dots,
lines or other divisional marks arranged in a circle and at equal distances apart.
This plate marked with the graduated circle may be made of translucent material the
divisional marks being opaque as above described or the plate may be opaque and the
divisional marks translucent-For instance in the latter case the plate may be made
of metal and the divisional marks may be holes through which light can pass. The
graduated circle plate being fixed in an upright position an opaque circular disc a
little larger than the graduated circle is placed parallel and very close to and con-
centric with the graduated circle-The opaque dise is perforated with a radial slot the
width of which is the same as that of one division on the graduated circle and the disc
is arranged so that it may be caused to revolve on its centre at any required speed.
In order to measure the speed of a shutter I set the disc in motion and keep it
revolving at a uniform rate say for example once in each second-I strongly illuminate
the graduated circle plate from behind with sun light, electric light the light of
burning magnesium or other sufficiently powerful illuminant and then using the
shutter to be tested with a lens and camera in the usual way I photograph as much of
the graduated circle as becomes visible through the revolving slot during the action
of the shutter-If the time of revolution of the disc is greater than the time of
exposure of the shutter the latter is shown by the number of divisions which appear
in the resulting photograph-For example if the disc be divided into one hundred
parts and be revolving at the rate of twice per second and twenty five divisions
appear in the resulting photograph then the time of exposure of the shutter is
evidently ths or one eighth of a second.
The revolving disc may be conveniently driven by having a small pulley attached
to and concentric with it this pulley being driven by a cord or band from any motor
working at a uniform rate. A water motor is very suitable for the purpose.
In the accompanying drawings Fig. 1 represents the graduated circle plate fitted to
the front of a box within which magnesium light or electric light may be placed in
order to illuminate the circle from behind-In this case the plate is supposed to be
opaque and the divisional marks translucent-A A is the circle plate and B B the
box C. C. are two fixed screws with fly nuts for the purpose of fastening the support of
the revolving disc in place-Fig. 2 represents the revolving disc mounted on a support

page_text: and fitted with pulley-D is the disc-S the slot-P the pulley-E is a pinion or
endless screw for the purpose of connecting the disc with a counting train of wheels
or other arrangement for registering the number of revolutions of the disc if it be
desired to do so.
I do not bind myself to the particular form of arrangement shown on the drawings
as the same may be varied without departing from the principle of my said invention.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed, I declare that what
I claim is
:-
For the purpose of measuring the time of exposure of photographic instantaneous
shutters, the use of a graduated circle plate illuminated from behind, in connection
with a revolving, opaque, slotted disc.