An Improved Instrument for Calculating the Time of Photographio Exposures.
Year: 1894

page_text: Date of Application, 30th Apr., 1894
Complete Specification Left, 17th Dec., 1894-Accepted, 19th Jan., 1895
PROVISIONAL SPECIFICATION.
An Improved Instrument for Calculating the Time of Photographio
Exposures.
I WILLIAM HENRY PHILLIPS, of 191, Stanhope Street, London N.W., Clerk,
do hereby declare the nature of this invention to be as follows:-
:―
My invention relates to that kind of photographic exposure meter in which au
actinometer for finding the intensity of the light is not required to be used, the
intensity of the light being taken from well-known tables compiled for this purpose,
a copy of one of such tables being supplied with the instrument.
An instrument of this kind to be complete must embrace four factors,-First--
subject. Second-plate. Third-light; and Fourth-diaphragm.
In practice, photographic cameras are not usually provided with shutters capable
of working at any required speed or of giving any required rate of exposure, and
it is usual to vary the size of the diaphragm in order to bring the length of exposure
within the capacity of the shutter of the camera, and also to bring it to a suitable
amount for the subject to be photographed. It is highly important therefore that
a photographic exposure meter should show, when once set, and opposite the scale
denoting the sizes of the diaphragms, the time of exposure suitable for each
diaphragm simultaneously, and the photographer will then be able to choose such
diaphragm as will require an exposure within the capacity of his shutter and still at
the same time a suitable one for the subject to be photographed ;-for instance, if
moving objects are to be photographed he must choose the shortest exposure at
which his shutter can work, as indicated on the scale, and use the diaphragm of the
size indicated for that exposure.
My invention consists of a slide-rule having upon it a date-table for the intensity
of light and five different scales, namely subject, plate, light, diaphragm & time
combined together in one instrument and arranged in such a way that the time
scale slides adjacent to the fixed diaphragm scale and shows for each size of
diaphragm simultaneously the time of exposure necessary. The other three scales
may be arranged in any order possible without affecting the action of the instrument,
any two of them being upon a moveable slider and the third one fixed, although I
prefer to have the subject scale fixed and the plate and light scales upon the
moveable slider; thus, although my instrument has upon it five different scales, yet
there are only two moveable slides and therefore only two adjustments to make.
The instrument is set by moving the slider until the number representing the speed
of the plate is opposite the name of subject to be photographed, the time slide then
being set so that a pointer which it carries is opposite the number on the first slider
representing the intensity of the light, the time of exposure will be found simul-
taneously opposite each diaphragm on the scale. I thus arrange my instrument so
that it not only indicates the necessary length of exposure, but also a suitable
diaphragm to use.
Although I prefer to arrange the above scales in the form of a straight slide-
rule, yet another form of the instrument consists in arranging them as segments of
circles, the scale of time being marked on the circumference of a central disc
revolving on its axis, and carrying a pointer, the other slider with the two scales
upon it being a segment of a larger disc and moving in a semi-circular slot adjacent
to the circumference of the central revolving disc, and the diaphragm scale and the
other fixed scale occupying various segments of a larger fixed disc, and in positions

page_text: adjacent to the scales to which they have reference, the setting of this form of the
instrument being exactly as described for the previous one.
Dated this 28th day of April 1894.
An Improved Instrument for Calculating the Time of Photographic
Exposures.
I, WILLIAM HENRY PHILLIPS of 191, Stanhope Street, London, N.W., Clerk,
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 that kind of photographic exposure meter, in which an
actinometer for finding the intensity of the light is not required to be used, the
intensity of the light being taken from well-known tables conspiled for this purpose
a copy of one of such tables being supplied with the instrument.
An instrument of this kind to be complete must einbrace four factors:- -First,―
subject; second,-plate; third,-light; and fourth,-diaphragm.
In practice photographic cameras are not usually provided with shutters capable
of working at any required speed or of giving any required rate of exposure, and it
is usual to vary the size of the diaphragm in order to bring the length of exposure
within the capacity of the shutter of the camera and also to bring it to a suitable
amount for the subject to be photographed. It is highly important therefore that
a photographic exposure meter should show when once set and opposite the scale
denoting the sizes of the diaphragms, the time of exposure suitable for each
diaphragm simultaneously; and the photographer will then be able to choose
such diaphragın as will require an exposure within the capacity of his shutter
and still at the same time a suitable one for the subject to be photographed :-
For instance, if moving objects are to be photographed he must choose the
shortest exposure at which his shutter can work as indicated on the scale, and
use the diaphragm of the size indicated for that exposure.
My invention consists of a slide-rule having upon it a date-table for the
intensity of light; and five different scales namely:-Subject, plate, light,
diaphragm, and time, combined together in one instrument and arranged in such
a way that the time scale slides adjacent to the fixed diaphragm scale and shows
for each size of diaphragm simultaneously the time of exposure necessary.
The
other three scales may be arranged in any order possible without affecting the
action of the instrument, any two of them being upon a movable slider, and the
third one fixed, although I prefer to have the subject scale fixed and the plate
and light scales upon the movable slider; thus although my instrument has upon
it five different scales yet there are only two movable slides and. therefore only
two adjustments to make.
The instrument is set by moving the slider until the number representing the
speed of the plate is opposite the name of subject to be photographed; the time
slide then being set so that a pointer which it carries is opposite the number on
the first slider representing the intensity of the light, the time of exposure will be
found simultaneously opposite each diaphragm on the scale. Ithus arrange my
instrument so that it not only indicates the necessary length of exposure but also
a suitable diaphragm to use.
Although I prefer to arrange the above scales in the form of a straight slide-
rule, when constructing another form of the instrument I sometimes arrange the
scales as segments of circles; the scale of time being marked on the circumference

page_text: of a central disc revolving on its axis and carrying a pointer, the other slider with
the two scales upon it being a segment of a larger disc and moving in a semi-
circular slot adjacent to the circumference of the central revolving disc, and the.
diaphragm scale and the other fixed scale occupying various segments of a larger
fixed disc and in positions adjacent to the scale to which they have reference,
the setting of this form of the instrument being exactly as described for the.
previous one.
In the accompanying sheet of explanatory drawings, Fig. 1 shows my invention
in the form of a straight slide rule of box-wood or other suitable material on the
body of which is a date table A, a subject scale B, and a diaphragm scale C.
The slide D carries two scales, the upper one for speed of plates and the lower
one for the intensity of light.
The slide E carries the time scale and a fixed pointer. I sometimes arrange two
or more fixed pointers, or one adjustable pointer to make corrections for variations
in the brightness of the sky, three fixed pointers being shown in the drawing
opposite the words :-Shine, Cloud, and Dull, respectively.
To obtain a reading upon the instrument shown, 1 first set the slide D so that
the number representing the speed of the plate is opposite the name of the subject
to be photographed. I then set the slide E so that the pointer on it marked
shine," "cloud," or "dull," (as the state of the sky may happen to be at the
time), is opposite the number on the slide D representing the intensity of the light,
this number being found from the date table. The correct exposure will then be
shown simultaneously opposite to each of the twenty-one diaphragms marked on
the scale.
The instrument is shown set for taking a portrait with dry plates of a speed of
40 times wet collodion plates at mid-day in June with the sun shining;-the speed
No. 40 on D being opposite the word,portrait," and the slide E set so that the
pointer marked "shine" is opposite the number 1 in the light scale on D, this
number being taken from the date table for mid-day in June. The time of
exposure will now be found on the slide E opposite each size of diaphragm and
will be seen to be for diaphragm second, for diaphragm
second, and
so on.
F
F 1
5 25
=
In Fig. 2 I have shewn my invention made up in a circular form, the body of
the instrument being a disc of card, metal or other suitable material and carrying
the date table A, the subject scale B and the diaphragm scale C. A second and
smaller disc H carries the time scale and its pointer or pointers, three being shown
marked respectively "shine," " cloud," and " dull." This smaller disc I make to
revolve on its axis ou a pivot attached to the centre of the large disc, in such a
manner that the time scale reads adjacent to the diaphragın scale. The other two
scales are on a segment of a third disc J one portion which carries the plate speed
scale being of the same radius as the disc H and covering up a portion of the time
scale on H so as to read adjacent to the subject scale on the large disc, the opposite
portion is of smaller radius aud carries the scale for light and moves adjacent to
the pointers on the disc H.
The segment J is mounted at its centre on a sleeve or pivot attached to the centre
of the disc H and moves thereon, when adjustment has to be made between J and H
by means of the pointers on H and the light scale on J, but at all other times J
and H are intended to revolve together and may be made to do so if necessary by
au ordinary spring or slot catch, and so that when once set no further movement
between them will be necessary so long as the brightness of the sky and the time
of day and year remain the same. The only thing then necessary to obtain a
reading being to move J and H round together until the plate speed number on J
is opposite the name of the subject on the scale B; when the correct exposure will
at once be found opposite each diaphragm number. It will thus often be possible
in this circular form of the instrument to obtain a reading by only one setting of
the instrument.

page_text: 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 :-
1. An improved instrument for calculating the time of photographic exposures
substantially as hereinbefore described and as illustrated in the accompanying
drawings.
2. In an instrument for calculating the time of photographic exposures the con-
struction and arrangement of a pair of slides working upon or within a flat rule disc
or tablet and displaying five scales and a date table; the time scale moving
adjacent to the diaphragm scale and giving the correct exposure for all the
diaphragms at one setting, substantially as herein before described.
Dated this 14th day of December 1894.
MARKS & CLERK,
18, Southampton Buildings, London, W.C., Agents.
MARKS & CLERK,.
18, Southampton Buildings, London, W.C., Agents.