Improved Means for Regulating the Rays of Light Passing Through Photographic Lenses.
Year: 1893

page_text: COMPLETE SPECIFICATION.
Improved Means for Regulating the Rays of Light Passing Through
Photographic Lenses.
I, JAMES WILLIAM FAWCETT, of "Berthanga
No. 15 Argyle Street
St. Kilda near Melbourne in the Colony of Victoria, Civil Engineer, 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:---
With the means at present in use for regulating the rays of light passing through
photographic lenses, it has been usual to make the apertures in the stops and
shutters in a line or concentric with the optic centres of said lenses. With this
construction, however, the major portion of the rays of light pass on to the sensitive
plate from the sky or upper portion of the landscape, whilst only a small portion
pass from the foreground, the effect upon such plate being unequal, so that it has
been found to be impossible under ordinary conditions to correctly photograph
clouds and other aerial effects at the same time as the foreground or main part of
the land or seascape.
Now the object of this invention is chiefly to enable these results to be obtained,
and partly to impart a stereoscopic effect to the photograph.
It consists in arranging the apertures in the diaphragms, stops and shutters of
photographic lenses so that their larger area is below the optic centre of the lens,
thereby allowing a greater proportion of light to pass from the foreground on to
the sensitive plate than from the sky, thus tending to equalise the effect upon the
plate, as will be well understood by photographers.
According to my invention, I make the lens aperture of triangular or approxi-
mately triangular shape, with the base arranged horizontally, and I cut a similarly
shaped opening in a horizontally sliding plate or shutter, which may be actuated by
hand or by any other convenient means.
By forming the aperture in the horizontally sliding plate or shutter, as just
described, and by sliding it horizontally, a stereoscopic effect is given to the .
finished photograph by reason of the light being allowed to enter first at one
bottom corner, then gradually being allowed to pass through the whole of the lens
aperture, and finally through a small opening at the opposite bottom corner, thus
as it were to a certain extent photographing the object from two different points of
view, and so producing the desired effect.
In order to reduce the size of this lens aperture, a plate having a triangular or
approximately triangular hole or notch cut in its lower end may be arranged to
slide vertically through a slot in the brass mount of the lens in the same way as the
ordinary stops, said plate being capable of adjustment to any required position so as
to cut off more or less of the upper part of the lens aperture.
I prefer to make the lens aperture in the form either of an equilateral or else of
an acute angled isosceles triangle, and arrange it so that two-thirds of its height is
below the optic centre.
The principle of construction above described can be applied to detachable,
instantaneous, or other shutters, such as are usually fitted upon the forward part of
the lens.
Referring to the accompanying drawings:
Figure 1 is a front elevation of a photographic lens fitted with my improvements,
whilst
Figure 2 ion plan thomas

page_text: Figure 7 is a front elevation of a detached shutter, constructed according to this
invention.
The same letters of reference indicate the same or corresponding parts in all the
figures.
A represents the aperture in the diaphragm, a, which aperture is, according to
this invention, so arranged that its major portion is below the optic centre B of the
lens. By preference I make this opening in the formreithery of an, equilateral or
else of an acute angled isosceles triangle, and arrange it so that only one-third of
its height projects above said optic centre B, thus leaving but a very small, area
above said centre, and placing the largest area below,
The shutter C is made with a corresponding aperture D, and is arranged to slide
horizontally through the usual metallic mounting E of the lens. Said shutter can
be worked either mechanically or by hand, as preferred.
F represents a stop or plate, having its lower end cut out in an approximately
triangular shape, as illustrated at G in Figure 1. This stop is graduated, as
illustrated at H in said figure, so as to indicate the size of the lens aperture, when
said stop is fixed at any given height. It is used in the same way and for the same
purpose as the ordinary graduated stops.
I prefer to notch the lower end of the stop F with curved sides, as shown, instead
of straight, because it will then more gradually regulate the amount of light passing.
through the two lower corners of the lens aperture.
With a lens and shutter constructed as above described, it will be evident that
the major portion of the light will pass through the lower part of the lens and .be.
directed on to the upper part of the sensitive plate, whilst a smaller proportion. will
be directed on to the lower part of the plate. Moreover, as indicated in Figure 4,
as the shutter C is moved, one corner of the aperture D will first pass over the
adjacent corner of the aperture A, leaving a small triangular aperture for the.
passage of the light on one side and below the optic centre of the lens. Then, as
said shutter continues to be moved, the full aperture through the lens will be
uncovered, as indicated in Figure 5, and finally as the aperture D is moved to the
opposite side it will gradually reduce the size of the lens aperture, until finally there
is but a very small passage for the rays of light on the opposite side to the one on
which the opening, was first exposed.
This operation will be clearly understood on reference to Figures 4, 5 and 16,
and the effect of such operation will be as it were. to partially photograph the
view from two different standpoints, the final result being to produce a photograph
having a peculiarly sharp stereoscopic effect, which greatly enhances its interest
and beauty.
If preferred, the novel principle of construction above described can be used for
detachable shutters, such as are fitted upon one or other end of the lens, and are
usually actuated instantaneously by means of a spring, compressed air, or other-
wise. In the example of such a shutter illustrated in Figure 7, the aperture. A is
made triangular or approximately triangular, and the aperture. D in the travelling
band C is made of a corresponding shape, whilst said band is made to travel
horizontally across the shutter either by means of a coiled spring. released by a
catch or by any other convenient means, such as are commonly in use with
instantaneous. shutters. By this means the results above described. can. be
obtained.
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:
'
First. In means for regulating the rays of light passing through photographic
lenses, a diaphragm formed with an aperture, having its larger area below the optic
centre of said lens, substantially as and for the purposes herein described and.
explained and as illustrated in Figures to 6 of the accompanying drawings:
Second. In means for regulating the rays of light passing through photographic

page_text: lenses, a diaphragm having a triangular or approximately triangular-shaped aperture
arranged with its larger area below the optic centre of the lens, substantially as and
for the purposes herein described and explained and as illustrated in the accom-
panying drawings.
Third. In means for regulating the rays of light passing through photographic
lenses, a horizontally sliding shutter (such as C) having a triangular or approxi-.
mately triangular aperture (such as D) arranged with its larger area below the
optic centre of the lens, substantially as and for the purposes herein described and
explained and as illustrated in the accompanying drawings.
Fourth. In means for regulating the rays of light passing through photographic
lenses, the combination with a horizontally sliding shutter (such as C) formed with
a triangular or approximately triangular aperture, arranged with its larger area
below the optic centre of the leus (such as D), of a stop (such as F) formed with a
correspondingly shaped notch or aperture (such as G) and adapted to cut off or
reduce the size of the lens aperture, substantially as and for the purposes herein
described and explained and as illustrated in Figures 1 to 6 of the accompanying
drawings.
Dated this Sixth day of June One thousand eight hundred and ninety-three.