Improvements in Photographic Lenses or Objectives and in Apparatus connected therewith.
Year: 1892

page_text: Date of Application, 7th June, 1892-Accepted, 9th July, 1892
COMPLETE SPECIFICATION.
Improvements in Photographic Lenses or Objectives and in
Apparatus connected therewith.
I ANDREW JOHN STUART of Bretlands Rusthall Tunbridge Wells Madras
Civil Service retired, 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 consists in obstructing or cutting off the light by any means
whatever from the central portion of the surface of photographic lenses or objectives
single or compound.
In obstructing by any means whatever the rays of light which fall on the central
portion of the surface of such photographic lenses or objectives, so that the image
will be formed by the rays which fall upon that portion of the lens which is outside
the part so obstructed or covered up. The shape of such obstruction may be
circular, or oval, or of any other form.
Such obstruction may be caused by any mechanical means whatever, for instance
by a disc of metal or of any other substance in front of the lens, or by a disc of tin
foil or a disc or spot of paint or of any other substance adhering to the lens, or by
cutting the lens in such a manner as to obstruct the rays.
In the case of compound lenses or objectives such obstruction may be applied to
any or all the lenses of which the compound lens is constructed, or to the whole as a
compound lens.
Patent protection is sought for the above mentioned as well as for all other
possible ways of causing the obstruction described above.
The means of obstruction may be of such construction as to admit of the area
obstructed being varied at pleasure by the use of the principle of the "iris
diaphragm" or by a rotating carrier bearing discs of different sizes. Protection is
sought for the application of these or of any other mechanical means for enlarging
or reducing the area obstructed at pleasure.
The means by which such obstruction of light is obtained may for the sake
of convenience be called "a central diaphragm and will hereinafter be referred
to by that phrase.
Such "central diaphragm" in whatever manner constructed may be combined
with the ordinary diaphragm as now in general use so as to enlarge or contract the
area of the lens surface exposed, and by which the picture is formed; so also as to
limit the rays failing upon the outer portions of the plate to those coming from
one portion only of the lens or of so much of it as is exposed.
It is the combination of this use of the ordinary diaphragm, which is a part of
the ordinary construction of photographic lenses, with the obstruction in the centre
of the aperture by the "central diaphragm" which is the most important and novel
feature in the present improvement.
It is believed that by this invention a better illumination will be obtained
especially in the outer parts of the field or plate, a more even illumination resulting
in more even development, and in more equal density in the picture when finished,
better definition, in the outer portions of the field especially, more rapidity in the
lens, with less distortion and more flatness of field.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
1. Protection for the use of the "central diaphragm" as above described in the
construction or use of photographic lenses or combinations of lenses or objectives as
such are now constructed or used.

page_text: 2. For the use of the said "central diaphragm " either by itself or in combination
with diaphragms of the ordinary kind now in use, in the manufacture or use of
photographic lenses or objectives whether single or compound.
3. The application of the principle of the iris diaphragm, or of a rotating carrier
bearing discs of different sizes or of any other mechanical contrivance for varying
at pleasure the area obstructed by the "central diaphragm."
Dated this 7th day of June 1892.
ANDREW JOHN STUART.