AN IMPROVED PHOTOGRAPHIC LENS
Year: 1857

page_text: LETTERS PATENT to Thomas Grubb, of the City of Dublin, Engineer,
for the Invention of "AN IMPROVED PHOTOGRAPHIC LENS."
Sealed the 6th April, 1858, and dated the 8th October 1857.
PROVISIONAL SPECIFICATION left by the said Thomas Grubb. at the
Office of the Commissioners of Patents, with his Petition, on the 8th
October 1857.
I, THOMAS GRUBB, of the City of Dublin, Engineer, do hereby declare
the nature of the said Invention for "AN IMPROVED PHOTOGRAPHIC LENS," to
be as follows:-
My improved photographic lens is most advantageously applicable as a
substitute for that lens in ordinary use by photographers, known as the "view
lens." My improved lens is similar to ordinary view lenses. so far as being a
nearly achromatized compound of crown (or plate) and flint glass lenses, and
the outward general form is also similai, but the internal construction is quite
different, the crown glass necessarily taking the place of the flint. and the flint
glass that of the crown (as respects the position in which the compound lens
is placed for use). and also the forms of the crown and flint lenses of my.
improved compound lens are essentially different to the same in ordinary "view
lenses."
My photographic lens is constructed as follows:-1 form a crown (or plate)
glass lens of a suitable focus, and of the form approaching that known as plano-
convex (by preference, one surface is made slightly concave, ane the lens is a
LD
037

page_text: meniscus).
Secondly, I form a flint lens, one side concave, and of the same
radius of curvature as the convex side of the crown lens, and the other side of
the flint lens I form of that curvature which will cause this lens to form with the
crown lens previously described an achromatized compound, and which will
necessarily be a convex surface. Lastly, I place the lenses so together that
the concave side of the flint and the convex side of the crown lenses shall be
adjacent.
My improved compound lens thus formed is to be placed when used in the
ordinary manner of a view lens, so that its crown lens is next the object or
more parallel rays, and the flint glass next the image formed by the lens of
same,
SPECIFICATION in pursuance of the conditions of the Letters Patent. filed
by the said Thomas Grubb in the Great Seal Patent Office on the
8th April 1858.
TO ALL TO WHOM THESE PRESENTS SHALL COME, 1, THOMAS
GRUBB, of the City of Dublin. Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Eighth day of October, in the year of our Lord One
thousand eight hundred and fifty-seven, in the twenty-first year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
Thomas Grubb, Her special licence, that I. the said Thomas Grubb, my
executors, administrators, and assigns, or such others as T. the said Thomas
Grubb, my executors, administrators. and assigns. should at any time agree
with, and no others, from time to time and at all times thereafter during the
term therein expressed. should and lawfully might make, use, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for" AN IMPROVED PHOTOGRAPHIC LENS,"
upon the condition (amongst others) that I, the said Thomas Grubb, my
executors or administrators, by an instrument in writing under my, or their.
or one of their hands and seals, should particularly describe and ascertain
the nature of the said Invention. and in what manner the same was to be
performed, and cause the same to be filed in the Great Seal Patent Office
within six calendar months next and immediately after the date of the said
Letters Patent.
NOW KNOW YE. that I, the said Thomas Grubb, do hereby declare the
nature of my said Invention, and in what manner the same is to be performed,

page_text: to be particularly described and ascertained in and by the following state-
ment thereof, reference being had to the Drawings hereunto annexed, that
is to say:
The crown glass
My improved photographic lens is most advantageously applicable as a
substitute for lenses in ordinary use by photographers, and known as "view
lenses." My improved lens is similar in several respects to ordinary view
lenses. It has the same general outward form. also it is a nearly achromatized
compound of two lenses of crown (or plate) and flint glass. the inner surfaces
of which are (by preference) formed of the same radius, one convex, the other
concave, so as to admit of the lenses being cemented. as in ordinary view
lenses. But the internal construction of my lens is essentially different to
that of either ordinary view lenses or other photographic lenses extant, the
crown glass taking the place of the flint, and the flint glass that of the crown
in my improved lens as compared with ordinary photographic lenses, and as a
necessary result of this transposition, both crown and flint lenses of my photo-
graphic combination assume essentially different forms as compared with the
corresponding lenses of other photographic compounds.
which in the ordinary view. lens is doubly convex, becomes in my lens nearly
plano-convex, usually slightly concave on one side, and the flint lens (usually
concave on both sides) becomes in my improved lens deeply convex on one
side, also the inner or separating curve of the two lenses of the compound
becomes inverted in its position, and much deeper in my lens as compared
with ordinary photographic lenses. The result being, that my improved lens
used as a view lens has its spherical aberration much more nearly corrected.
and consequently it forms more distinct images of objects than either the
ordinary view lens, or the front compound lens of a "portrait combination," as
occasionally used by photographers as a view lens. I do not, however, limit.
myself in the use of my improved lens to that of taking of views, or of being
used alone. The lens admits of entering with advantage into combination
with one or more other lenses of either similar construction to itself, or of
other or ordinary constructions.
And the manner in which I construct my improved photographic lens is as
follows: form a lens of crown (or plate) glass of a suitable focus, and of a
form approximating to that known as plano-convex: one surface is generally.
by preference, made slightly concave, and the lens is in such case a "meniscus."
Secondly, I form a lens of flint glass, one side (or surface) concave, and (by
preference) of the same radius of curvature as the deeper side of the crown
lens, and the other or second side of this flint lens I form of that curvature
which will cause the lens to form with the crown lens previously described a

page_text: nearly achromatized compound, or more strictly speaking a compound cor
rected for actinic dispersion, and which second surface of the flint lens will
necessarily be a convex surface. Lastly, I place the two lenses together with
or without a cement or fluid interposed, so that the surfaces of similar radii
shall be adjacent. The compound or improved photographic lens thus formed.
is placed in a similar position for use, in respect of the outward general form,
as an ordinary photographic lens.
And in further explanation of the nature and construction of my improved
lens, give the accompanying sectional Drawings, of which Figure 1 repre-
sents an ordinary "view lens," and Figure 2 one of my improved lenses.
a, a, in both Figures represent flint glass, and b crown glass, both Figures
representing compounds of the same focal length and external form, and com-
pounded of lenses made of the same kinds of crown and flint glass. and of the
same foci respectively. but which differ essentially in their respective forms.
and also occupy inverted places in their respective compounds, thus necessarily
causing the inner or separating curve to be inverted, and also much deeper in
my improved lens. It is in this great increase in the depth of the internal
curvature that the great superiority of my improved lens mainly resides.
And having now described the nature of my said Invention, and in what
manner the same was to be performed. I declare that what I claim is, an
improved photographic lens constructed in the manner before described, and
used either alone and as a "view lens," or in combination with other lenses of
similar or ordinary construction, the distinctive characteristics of the construc-
tion of my lens being, that the two kinds of glass of which it is formed occupy
inverted places in the compound, and that the internal or separating curve is
also inverted, and much deeper in my improved lens as compared with
ordinary or existing photographic lenses.
In witness whereof, I, the said Thomas Grubb, have hereunto set my
hand and seal, this Fifth day of April. One thousand eight hundred
and fifty-eight.
THOMAS GRUBB. (L.s.)