AN AUTOMATIC ADJUSTABLE PHOTOGRAPHIC EXPOSER.
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by George Leonard Addenbrooke at the
Office of the Commissioners of Patents on the 4th April 1882.
GEORGE LEONARD ADDENBROOKKк, of No 9 Mecklenburgh S in the County of
Middlesex, Gentleman, AN AUTOMATIC ADJUSTABLE PHOTOGRAPHIC EXPOSER.
My invention is for the purpose of enabling Photographers to obtain readily
the exact exposure which they may deem proper to give photographic plates in the
camera.
Several forms of photographic shutters are now in use to which my invention
may be rendered applicable. But I prefer a form of shutter made as follows;—
A closed box say 8 in. long, 4 in. broad, & 1%, inch thick (these measures being
proportionate) through the lower part of which a hole is made (say 8 in. in diameter).
This box should have inside it two grooves in which work freely two slides of such
size as to cover the aperture. These slides are attached by Elastic or springs, one
to the top & the other to the bottom of the box. When required to be set, one
slide is drawn down to cover the aperture & the other is drawn into the space above,
both being retained by catches.
I now proceed to describe my method of withdrawing the catches as in the
shutter above described, so as to regulate exposures.
I fix on the shutter in any convenient place a simple clockwork train almost
exactly similar to the striking train of a clock, & consisting of a long spring preferably
with stopwork to prevent its being wound more than one turn.
To the barrel of this spring is on one side geared a revolving fan the gearing
being such as to cause the fan to make, say from 800 to 600 revolutions. for one
revolution of the spring barrel. The barrel of the spring is also geared into a cog
wheel of rather smaller diameter than the barrel. The arbour of this cog wheel
projects through the case of the clockwork, & to it is fixed a metal disc. This disc
has on the underside a projection, & a lever working on a central pivot is placed so
as to come in momentary contact with this projection as the diso revolves. This
lever is connected by a simple metal rod or slip to the lower catch of the shutter
which is made with an arm projecting at right angles so as to receive it, so that
whenever the projection on the disc moves the lever the catch is withdrawn & the
slide it holds liberated.

page_text: Again the disc has a moveable radial arm having another projection rather
further from the centre than the first & by any convenient means, such as a series
of holes at graduated distances round the edge of the disc this second projection
may be set at any required interval from the first. This second projection acts on
another lever similar to the first described & connected in like manner with the
upper catch of the shutter. It is thus clear that the disc being set to revolve in a
certain number of seconds (say 3) the two levers will be moved by the two projections
at an interval which bears the same relation to the time taken for a whole revolution
of the disc as the arc distance between the points does to the whole circle. The
result being that. the operator having wound up the spring, set the radial arm to
give a required exposure, & the slides of the shutter. On liberating the clockwork,
the slides rise & fall respectively at the interval fixed upon, so making the
required exposure.
Claims,
I do not claim as part of my invention the use of the shutter above described,
but I do claim as my invention,-(1) The use of a simple clockwork train governed
by a fan to regulate Photographic exposures, such clockwork train to release both
shutters, or their equivalents in other forms of shutter, when the apparatus is wound
up, the shutter set &, the fly released. (2) The use of a rotating disc with two
projections or their equivalent for the purpose of regulating photographic exposures,
as above described.