Improvements in Lenses for Light-houses, Projecting Apparatus, and the like.
Year: 1898

page_text: Improvements in Lenses for Light-houses, Projecting Apparatus, and
the like.
We, MESSRS. BARBIER & BENARD, of 82, Rue Curial, Paris, France, Light-house
Engineers, do hereby declare the nature of this invention to be as follows:-
This invention relates to lenses suitable for lighthouses projecting apparatus
and the like and comprising dioptric and catadioptric rings or lenses arranged to
subtend an angle up to about 180°, and constructed in such a manner that the
focal distance of almost all the elements will be practically the same. This
arrangement allows of the use of lanterns of small size relatively to the focal
distance of the dioptric lens.
Lenses in accordance with this invention are composed of a central spherical
lens 1 surrounded by plano-convex dioptric rings 2 arranged in receding tiers as
shown in Fig. 1 of the accompanying drawings. The catadioptric portion, which
is the principal feature of this invention, consists of rings 3 of a novel shape,
(designated the "Rutishauser" shape) the section of which is somewhat similar
to the central part of a concavo-convex lens, cut through by a straight line, which
becomes the reflecting surface, as shown in Fig. 2.
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00
The radii of curvature of the lens taken as the basis may vary from.
to co that is to say, the principal sections of the surfaces of incidence and
of emergence of the prism may be convex or concave, with any desired radii of
curvature, the principal section of the catadioptric ring always comprising a
straight line as a reflecting surface.
This system of rings allows furthermore of reducing the angles of incidence
and of emergence of the rays, and consequently of reflecting the light under better
conditions.
In Fig. 2 is represented the central part M, N, P, Q, of a concavo-convex lens
arranged in such a manner that the rays striking at point F shall emerge at the
second surface of the lens parallel to the axis; thus if F C is a ray which on the
surface P Q undergoes a first refraction which deflects it to C E¹, this ray meets
the face M N which renders it at 11 parallel to the axis X', as indicated by the
line D¹ Y¹.
If now this element of a lens be cut by a straight line C, B in such a manner
that all the refracting rays make with it an angle which is smaller than 45° (in

page_text: reality smaller than 49°, 11", for crown glass having an index of refraction equal
to 1.53) and that the rays which would otherwise emerge at the face M N shall
become parallel to the axis of the apparatus, as indicated by the line ✗ the
annular prism will be represented in section by the quadrilateral Figure CBK D
(the part A DK not being of any use).
From the foregoing it will be seen that a lens constructed and arranged accord-
ing to this invention is composed of a dioptric lens formed of an indefinite number
of elements similar to those of the ordinary lenses of lighthouses, having rectilinear
or curvilinear internal surfaces, but placed so as to recede one on the other
according to a variable or any desired inclination, and capable of embracing or
subtending an angle up to approximately 90°, and 'a series of convexo-concave
lenticular elements. having a rectilinear reflecting surface, (designated "Rutis-
hauser,") as above described, which, when coupled with the ordinary dioptric
elements complete up to 180° the condensing power of a cylindrical or annular
lens.
.
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C.,
Agent for the Applicants.
COMPLETE SPECIFICATION,
Improvements in Lenses for Light-houses, Projecting Apparatus,
and the like.
We, MESSRS. BARBIER & BENARD, of 82, Rue Curial, Paris, France, Light-house
Engineers, 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:
:
This invention relates to lenses suitable for lighthouses, projecting apparatus
and the like, comprising dioptric and catadioptric rings or lenses arranged to
subtend an angle up to about 180°, and constructed in such a manner that the
focal distance of almost all the elements will be practically the same. This
arrangement allows of the use of lanterns of small size relatively to the focal
distance of the dioptric lens.
Lenses in accordance with this invention are composed of a central spherical
lens 1 surrounded by plano-convex dioptric rings 2 arranged in receding tiers
as shown in Fig. 1 of the drawings filed with our Provisional Specification. The
catadioptric portion, which is the principal feature of this invention, consists of
rings 3 of novel shape (designated the "Rutishauser" shape). the section of which
is somewhat similar to the central part of a concavo-convex lens, cut through by
a straight line, which becomes the reflecting surface, as shown in Fig. 2.
The radii of curvature of the lens taken as the basis may vary from
too; that is to say, the principal sections of the surfaces of incidence and
of emergence of the prism may be convex or concave, with any desired radii of
curvature, the principal section of the catadioptric ring always giving a straight
line as regards the reflecting surface.
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00
This system. of rings allows furthermore of reducing the, angles of incidence
and of emergence of the rays, and consequently of reflecting the light under better
conditions.
:
In Fig. 2 is represented the central part M, N, P, Q, of a concavo-convex lens
arranged in such a manner that rays issuing from point F shall emerge at the
second surface of the lens parallel to the axis; thus-F.C is a ray which on the

page_text: surface P Q undergoes a first refraction which deflects it in the direction C E',
this ray meets the face M N at D' where it is again refracted and emerges parallel
to the axis X', as indicated by the line D¹ Y¹.
If now this element of a lens be cut by a straight line C, B in such a manner
that all the refracting rays make with it an angle which is smaller than 45° (in
reality smaller than 49°, 11', for crown glass having an index of refraction equal
to 1.53) and that the rays which would otherwise emerge at the face M N shall
become parallel to the axis of the apparatus, as indicated by the line X the
annular prism will be represented in section by the quadrilateral Figure CBK D
(the part A D K not being of any use).
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed we declare that what we
claim is:-
1. A lens, suitable for lighthouses, projecting apparatus and the like comprising
a dioptric lens formed of a number of elements similar to those of the ordinary
lenses of lighthouses, having rectilinear or curvilinear internal surfaces, but
placed so as to recede one on the other according to a variable or desired inclina-
tion, and capable of subtending an angle up to approximately 90°, and a series
of convexo-concave lenticular elements having a rectilinear reflecting surface as
above set forth, and which, when coupled with the ordinary dioptric elements or
with the dioptric elements above described complete up to 180° the condensing
power of a cylindrical or annular lens, substantially as described.
2. In lenses and lenticular apparatus, the construction and use of the convexo-
concave reflecting rings herein before described.
3. The use of elements having the sectional form hereinabove described for
the
purpose of forming cylindrical lenses or lenses of fixed focus, annular lenses or
projecting lenses, and flashing lenses for ordinary revolving lights or flash lights,
electric and other projecting apparatus.
4. The improved lens constructed arranged and operating as hereinbefore des-
cribed with reference to and shown in the drawings referred to.
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101
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C.,
Agent for the Applicants.
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C.,
Agent for the Applicants.