IMPROVE- MENTS IN THE CONSTRUCTION OF LENSES, WHICH IMPROVEMENTS ARE ESPECIALLY APPLICABLE TO LENSES FOR PHOTOGRAPHIC PURPOSES
Year: 1864

page_text: LETTERS PATENT to John Henry Dallmeyer, of 19, Bloomsbury Street,
in the County of Middlesex, Optician, for the Invention of " IMPROVE-
MENTS IN THE CONSTRUCTION OF LENSES, WHICH IMPROVEMENTS ARE ESPECIALLY
APPLICABLE TO LENSES FOR PHOTOGRAPHIC PURPOSES."
Sealed the 17th March 1865, and dated the 14th October 1864..
PROVISIONAL SPECIFICATION left by the said John Henry Dallmeyer
at the Office of the Commissioners of Patents, with his Petition, on the
14th October 1864.
I, JOHN HENRY DALLMETER, of 19, Bloomsbury Street, in the County of
Middlesex, Optician, do hereby declare the nature of the Iuvention for "IM.
PROVEMENTS IN THE CONSTRUCTION OF LENSES, WHICH IMPROVEMENTS ARE ESPECIALLY
APPLICABLE TO LENSES FOR PHOTOGRAPHIC PURPOSES," to be as follows:-
This Invention has for its object improvements in the construction of lenses,
whichimprovementsareespeciallyapplicabletolenses for photograph purposes.
My improved lens ischieflyintended for landscape photography,andfromthe
nature of its construction embraces a larger angle of view with more perfect
correction of both the spherical and chromatic aberration of the oblique or
eccentrical pencils than theform of lenses hitherto used for that purpose, viz.,
the ordinary view lens and that known bythe name of "Aplanatic view lens,"
patented by Thomas Grubb, of Dublin, on the Sth October 1857 (No. 2574).
My improved lens is composed of three lenses, by preference cemented
Brin8t

page_text: together, two of which are made of crown or plate glass, by preference of two
different kinds of crown or plate glass, and between the two is positioned a
flint glass lens. Thus both external lenses are made of crown or plate glass,
and both external surfaces belong to the crown or plate glass lenses. Whereas
in the existing forms of view lenses referred to, consisting of two lenses only,
one of crown and the other of flint, one surface of the crown and one of the
flint is necessarily exposed, and this latter surface is liable to be affected by
atmospheric influences.
The construction of my improved photographic lens is as follows:-I form
two lenses of crown or plate glass, by preference of twodifferent kindsofcrown
or plate glass,and divide for a given focal length, the focal power between the
two lenses, by preference in the ratio of 1 to 3, both acting therefore as positive
or collecting lenses. The form of the first or anterior crown or plate lens is by
preference a concave meniscus. The second or posterior crown or plate lens
is also by preference, a concave meniscus. The central lens situated between
the two crown or plate glass lenses is made of flint glass and concave-convex
by preference, and of such focal power as when placed between the two.crow
plate glass lenses the adjacent surfaces having the same radii of curvature
and being cemented produces an achromatic whole, or nearly so.
Externally, as, a whole,my improved photographic lens. resembles the view
lenses at present in use.its positions with reference to the diaphragmn is also
nearly the same.
My improved photographic lens may also be advantageously, employed,
either singly or in combination with one or more lenses for other purposes.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed;
by the said John Henry Dallmeyer in the Great Seal Patent Office.
on the 12th April 1865.
I₁
JOHN
TO, ALL TO WHOM THESE PRESENTS SHALL COME,
HENRY, DALLMEYER, of 19, Bloomsbury. Street, in the County of Middlesex,
Optician, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Fourteenth, day of October, in the yearofourLord One
thousand eight hundred, and sixty-four, in the twenty-eighth year of Her
reign,did for Herself, Her heirs andisuccessors,give and grant unto me, the
said John Henry. Dallmeyer. Her special licence that I, the said John
Henry Dallmeyer, my executors,administrators,and assigns, or such others as

page_text: I, the said John Henry Dallmeyer, 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 "Im-
PROVEMENTS IN, THE CONSTRUCTION OF LENSES, WHICH IMPROVEMENTS ARE ESPECIALLY
APPLICABLE TO LENSES FOR PHOTOGRAPHIC PURPOSES," upon the condition (amongst
others) that I, the said John Henry Dallmeyer, 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 Inven-
tion, 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 John Henry Dallmeyer, do hereby
declare the nature of the said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement thereof, that is to say: -
This Invention has for its object improvements in the construction of lenses,
which improvements are especially applicable to lenses for photographic
purposes.
My improved lens is chiefly intended for landscape photography, and from
the nature of its construction embraces a larger angle of view with more
perfect correction of both the spherical and chromatic aberrations of the
oblique or excentrical pencils than the forins of lenses hitherto used for that
purpose.
;
My improved lens is composed of three lenses by preference cemented
together, two of which are made of crown or plate glass, by preference of two
different kinds of crown or plate glass, and between the two is positioned a
flint glass lens. Thus both external lenses are made of crown or plate glass,
and both external surfaces belong to the crown or plate glass lenses. Whereas
in the existing forms of view lenses referred to, consisting of two lenses, only
one of crown and the other of flint, one surface of the crown and one of the
flint is necessarily exposed, and this latter surface is liable to be affected by
atmospheric influences.
The construction of my improved photographic lens is as follows:-I form
two lenses of crown or plate glass, by preference of two different kinds of crown
or plate glass, and divide for a given. focal length the focal power between the.
two lenses, by preference in the ratio of 1 to 3, both acting therefore as positive
or collecting leuses. The form of the first or anterior crown.or-plate lens is

page_text: by preference a concave meniscus. The second or posterior crown or plate
lens is also by preference a concave meniscus. The central lens situated
between the two crown or plate glass lenses is made of flint or glass and
concavo-convex, and of such focal power as when placed between the two
crown or plate glass lenses the adjacent surfaces having the same radii of
curvature and being cemented produce an achromatic whole, or nearly so.
Externally, as a whole, my improved photograpbic lens resembles the view
lenses at present in use, its position with reference to the diaphragm is also
nearly the same.
My improved photographic lens may also be advantageously employed
cither-single-or-in-combination with one or more lenses for other purposes.
And in order that my said Invention may be most fully understood and
readily carried into.effect, I will proceed to describe the Drawing hereunto
annexed.
DESCRIPTION OF THE DRAWING.
The Drawing shows a vertical section of a lens constructed according to my
Invention, and suitable for use for photographic purposes. a is the anterior,
and the posteriorlens; they are of crown or plate glass, and by preference of
different qualities in order that, as is well understood by opticians, a more
perfect chromatic correction may be obtained. I prefer that the relation
between the radii of curvature of the concave surface of the lens a, and of the
convex surface of the lens b, should be as 2, 1, or thereabout, and also as
before-mentioned that their focal lengths should be in the relation of 1, 3, or
thereabout; c is the flint glass lens interposed between the lenses a and b, to
form a compound lens which is achromatic or nearly so; its curvatures I
prefer to correspond with those of the adjacent faces of the lenses a and b, so
that the three portions of the compound lens may be cemented together to form
a solid whole. There are however some special cases in which it is desirable
not to cement the lens a to the other portions of the compound lens, viz.
inlenses employed specially for photographing architectural objects, for it will
be found that the straightness of the lines will be better maintained if the
lens a is placed at a distance from the other parts of the compound lens; the
distance between the lenses a and c, which corresponds with the best perfor-
mance in this respect is easily found in each case by experiment, or it may be
ascertained by calculation. The diaphragm or stop I usually place at a dis-
tance of about one-twelfth of the focal length of the lens in front of the lens a
I would remark that it is not at all new to make compound lenses in three
parts with a centre negative lens of flint glass covered on both sides. with

page_text: positive lenses of crown or plate glass. Although such lenses are not usually
employed for photographic purposes, they are common in telescopes and
microscopes; in such compound lenses, however, the flint glass lens chas never
been made convex on either face, whereas it is an important feature in my
improved compound lens that this lens should be convex on one face. Here-
tofore also in such compound lenses consisting of three parts, the anterior
surface of the anterior lens a, has never been made concave, whereas it is an
important (although not absolutely an indespensible feature) of my improved
compound lens that it should be so made.
By my improvements a more perfect correction than heretofore of both the
spherical and chromatic aberrations of the oblique or excentric pencils
obtained, whilst at the same time the flint glass lens is protected from injury
by the crown or plate glass lenses ou either side of it.
In witness whereof, I, the said John Henry Dallmeyer, have hereunto
set my hand and seal, this Eleventh day of April, in the year of our
Lord One thousand eight hundred and sixty-five.
J. H. DALLMEYER. (L.S.)