IMPROVEMENTS IN COMPOUND LENSES SUITABLE FOR PHOTOGRAPHIC USES
Year: 1866

page_text: LETTERS PATENT to John Henry Dallmeyer, of 19, Bloomsbury Street,
in the County of Middlesex, Optician, for the Invention of "IMPROVEMENTS
IN COMPOUND LENSES SUITABLE FOR PHOTOGRAPHIC USES."
Sealed the 7th December 1866, and dated the 27th September 1866.
PROVISIONAL SPECIFICATION left by the said John Henry Dallmeyer
at the Office of the Commissioners of Patents, with his Petition, on the
27th September 1866.
I, JOHN HENRY DALLMEYER, of 19, Bloomsbury Street, in the County of
Middlesex, Optician, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN COMPOUND LENSES SUITABLE FOR PHOTOGRAPHIC USES," to be as
follows:-
All existing double combinations embracing large angles of view and used
with a small central diaphragm have the defect, more or less, of producing a
bright central spot in the picture. I have discovered that the cause of this
spot is the formation principally of an image of the aperture of the diaphragm
by the back combination. Now I have devised a double combination lens or
objective in which the formation of a central spot is practically avoided in
consequence of the stop being placed in a position which is unfavorable to
the formation of an image by the back or posterior combination, and this
combination is to be of smaller size or diameter as compared to the front

page_text: combination, since for a given position of stop or diaphragm the intensity of
illumination of the central spot varies with 'the diameter of the back
combination.
My improved photographic lens or objective is composed of two positive
combinations of unequal diameters, i. e., the front or anterior combination
is larger than the back or posterior combination, and the diaphragm or stop
is situated between the two combinations, dividing the distance between them
in proportion to. their diameters. The form of front and back combinations
is as follows: The anterior or larger combination is composed of a deep
concavo-convex of flint and a deep concave meniscus of crown, by preference,
the adjacent surfaces cemented, and the back or smaller combination is also
composed of two such similar lenses. I make the flint glass lens occupy the
exterior positions in both combinations, i. c., the convex surface of the flint
part of the front combination is exposed to the view or landscape, and that of
the back or posterior combination to the screen of the camera. By the choice
of suitable radii of curvitures and proximity of the two combinations I obtain
greater equality of illumination and definition throughout the entire surface
covered by the lens or objective than has been obtained hitherto with existing
double combination lenses embracing large angles of view. I give the
component elements of each combination such forms that the refractions at
the several surfaces composing the front and back combinations shall be equally
divided and be a minimum throughout, and by the adoption of a small interval
or distance between the two combinations, which by preference does not
exceed of the compound focus of the objective, I require for a given large
angle of view lenses of but comparatively small diameters or comparatively
small thicknesses, smaller and thinner for a given large angle of view than
the lenses composing any existing double achromatic or actinic combinations,
and by this means I obtain better correction of eccentrical pencils, or, in other
words, more perfect definition at the margin of the picture. I would remark
that my improved lenses or objectives differ from any double combination lenses
heretofore constructed consisting of two positive combinations, in that the
posterior combination is of smaller diameter than the anterior, and also in that
the two exterior surfaces, vizt., the surface next the view and the surface next
the screen or image are both of flint glass.
My Invention also relates to the construction of a double achromatic or
actinic combination especially designed for portrait pictures, but also
applicable for views, enabling the operator to introduce at will, by an altera-
tion in the distance or separation between the two elements composing one of
the combinations, any required amount of spherical aberration, for it is found

page_text: to be desirable and advantageous that instead of defining objects in one plane
only, as produced by a lens perfectly corrected for spherical aberration, that the
correction of a lens for spherical aberration should admit of being impaired
for the moment to suit the requirements of the artist or operator for a given
occasion, and made to define objects situated at various distances from the
lens, so that the operator may, by sacrificing intense sharpness of definition on
one plane and distributing it over several planes, obtain a more artistic and
pleasing result.
In the ordinary double combination portrait lens as originally invented by
Professor Petzval the ratio of aperture to focal length is about 1: 3 to 1: 6,
and the lenses or elements composing the back combination are each placed
in a position, as it were, of minimum spherical aberration, and therefore any
moderate amount of variation of distance between them does not sensibly
affect the correction for spherical aberration of the entire combination. Now
in my new lens or objective I reverse the position both as regards the order
and form of the component elements of this back combination, and I further
also modify or alter their form to obtain in addition to the correction for
spherical aberration the necessary amount of flatness of field, so that the
lenses in their altered condition have, as it were, each a maximum of
aberration, and then by a slight variation of distance or separation between
the two elements the state of correction of the entire combination or objective
may be altered at pleasure. Suitable means are provided for varying the
distance between these elements at the pleasure of the operator.
I would remark that lenses constructed according to this part of my Inven-
tion differ from double combination portrait lenses heretofore constructed, in
that in the posterior combination the flint lens is exterior or nearest the screen
or image, and the crown lens is nearest to or faces the front combination,
whilst at the same time the curvatures of the adjacent surfaces of the crown
and flint glass lens are dissimilar.
With the same object of regulating the spherical aberration at pleasure a
similarly constructed combination may be made to form part of other lenses
or objectives composed of more than two combinations, such as the triplet;
also (but less conveniently) the regulation of the spherical aberration may be
obtained by means of the anterior combination of a double combination, in
which case the anterior combination is made with the adjacent surfaces of its
clements of different curvatures and with the flint lens outside or towards
the view. Means are provided for slightly altering the distance between these
elements at pleasure.

page_text: 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
27th March 1867.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
HENRY DALLMEYER, of 19, Bloomsbury Street, in the County of Middlesex,
Optician, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Lotters
Patent, bearing date the Twenty-seventh day of September, in the year of our
Lord One thousand eight hundred and sixty-six, in the thirtieth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me,
the said John Henry Dallimeyer, Her special licence that I, the said John
Henry Dallmeyer, my executors, administrators, and assigns, or such others as
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 "IMPROVEMENTS
IN COMPOUND LENSES SUITABLE POR PHOTOGRAPHIC USES," 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 oneoftheir
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 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 :-
The first part of my invention relates principally to the production of view
lenses or objectives embracing large angles. Lenses or objectives constructed
according to my Invention differ from all existing double combination lenses
or objectives consisting of two positive combinations, in that the denser or
higher refractory medium, i. e., the flint glass lens occupies the exterior
position in both combinations, that is to say, the convex surface of the flint
part of the front combination is exposed to the view or landscape, and that of
the back or posterior combination to the screen of the camera, and also in
that the posterior combination is of smaller diameter than the anterior
combination.

page_text: And in order that my said Invention may be most fully understood I will
describe in detail the form I prefer for each of the parts.
For a lens or objective embracing an angle of about 100°; and of which the
15,
1
largestaperture is the construction is as follows, referencebeing ma
made to the
annexed Diagram Figure I. I form two similar combinations, as A and B, by
preference of identical focior nearly so, and in relation to f(which is the com
pound or equivalent focus of the entire objective) as 2: 1. Each combination
consists of a deep concavo-convex lens of flint glass, as a and a¹, and a deep
meniscus of crown glass, as band b1, the ratio of foci between a and b and a!
and 61 are such that for the qualities of glass which are being used each com
bination by preference is achromatic or actinic in itself. The diameter of the
front combination A is by preference of the compound focus of the objective...
or
r
, and the radius of curvature of the anterior surface of the flint glass lens a
is by preference also
""
4
5'
The radius of curvature of the fourth or concave surface
.:
of the crown lens isto, as 4:3. The internal surfaces, i.e.,, of flint lens a
and of crown lens b, are by preference identical and cemented, and such that
3
"
forthe above focal length and qualities of glass employed combination A may
be achromatic or actinic. The diameter of the back combination B is to that
of the frout combination A, by preference, as 1 : 2, and the radius of cur-
vature of the posterior convex surface of flint glass leus a¹ is to the radius
of curvature of the anterior convex surface 7 of flint lens,a by. preference
as 7: 6. The radius of curvature of concave surface of crown lens 61 is to
S
by preference as 4:3. The radii of curvatures of the internal surfaces, i.e.,
6.
of flint lens a¹ and of crown lens b¹, are by preference identical and
cemented, and such that for the above focal length and qualities of glass
employed combination B may be achromatic or actinic. The combina-
tions A and B are separated by an interval (i.e., the distance between
their internal surfaces) by preference equal to of the compound focal
length of the entire combination or objective, i.e. and the diaphragm or
stop C divides this space in the proportion of the respective diameters of A
and B. The improvements over existing double combination- lenses, free

page_text: from distortion and embracing large angles of view,secured by the arrangement
of lenses or objectives above detailed, are these:-1st, freedom from a
central spot in the resulting picture; 2nd, more perfect correction of the
central as well as eccentrical pencils both for spherical and chromatic
aberrations, hence for a given large angle of view the lens or objective admits
of the use of a larger aperture, or, in other words, it is quicker acting than
existing lenses constructed for similar purposes; 3rd, greater equality of
illumination throughout the entire surface of the plate covered by the lens.
According to the nature of requirement, however, other dimensions than those
given above can also with advantage be employed (as for lenses intended for
copying maps and plans only), still retaining the distinctive features of my
Invention herein set forth. I would remark that a lens may be constructed
according to my Invention of flint glass only, necessarily of two different kinds
as regards density, for the production of achromaticity, instead of as is usual
of crown and flint glass; then the denser or higher refractive flint glass lens of
each of the two combinations occupies the external or exterior position.
What I claim as respects this part of my Invention is the constructing of
lenses composed of two positive achromatic or actinic combinations of which
the higher refracting denser material or flint glass lens occupies the external
or exterior position in each combination; also the constructing lenses com-
posed of two positive achromatic or actinic combinations with the posterior
combination of smaller diameter than the anterior combination.
Another part of my Invention relates to double combination and other
lenses or objectives intended chiefly for portraiture, but also applicable for
views and other pictures, and consists in arranging them so that the lenses
composing one of the combinations is of such form and so positioned that by
a slight variation of distance or separation between its elements any desired
amount of spherical aberration can be obtained without at the same time
materially deranging the other necessary corrections of a photographic
objective or lens. With a lens or objective so constructed the operator can
by sacrificing intense sharpness of definition on one plane distribute the defini-
tion over several planes,and so obtain a more artistic and pleasing result. A
double combination lens or objective may be constructed according to my
Invention as is shown at Figure 2; it differs from double combination portrait
lenses such as that originally invented by Professor Petzval of Vienna, and
shown at Figure 3, in that the lenses composing the back combination are
reversed both as regards their order of position and form, i.c., the flint glass
lens is exterior or nearest the screen or image, and the crown glass lens ie
nearest to or faces the front combination, whilst at the same time the radii of

page_text: curvatures of the adjacent surfaces of the crown and flint glass lenses are
dissimilar, and suitable means are provided to alter the distance or separation
between these two lenses at will; then for my new lens the ratio of effective
aperture of which is to the compound focal length of the entire combination
as 1 : 3, the angle of field embraced about 60°, and the image free from
distortion.
3.
The details of construction are as follows, reference being made to theannexed
Diagram, Figure 2:-For a given compound or equivalent focal length fof the
entire combination or objective I construct two combinations, as A and B, both
of the same diameter equal to The ratio of focal length of the anterior
combination A is to the compound focus f as 9: 6, and the focal length of
the back combination B is to A as 3: 2. The front or anterior combination A
is composed of a double convex lens of crown glass a and a double concave
lens of flint glass b. The radius of curvature of the anterior surface of
the lens a is in proportion to the compound focus of the entire
combination or objective as 1 : 2, and the external radius of curvature
""
4
of flint glass lous is to 1 as 5: 1. The internal radii of curvature. of
""
2 22
crown lens a and of flint lens bare by preference identical and cemented,
"
3
2
and such that for the above focal length the combination A by preference is
achromatic, or nearly so, which for the qualities of glass employed by me is
the case when the ratio of radii between the. anterior and internal
surfaces, i.e., and of crown lens a, is as 31:27. At a distance equal to
the diameter of the front combination A is situated the posterior combi
nation B, composed of two lenses, viz., of, by preference, a meniscus lens of
crown glass al with the concave surface facing the front combination, and of
a concavo-convex lens of flint glass b', convex side outside or facing the
screen of the camera, those two lenses having their adjacent surfaces
dissimilar. The radius of curvature of the adjacent or internal convex
surface of crown lens a¹ is in proportion to the radius of curvature of the
ji
6
) anterior surface of crown lens a as 2: 3, and the posterior or external
1°
1"
radius of curvature
8
of flint lens is to as 37 31. The radii of cur-
1
vatures of the other two surfaces, viz., the concave surface of crown

page_text: The combination or objective constructed as above without any diaphragm
and with the component lenses of combination B, as separated above, viz., at
60'
a distance equal to 6, is free from spherical and chromatic aberration for
both the axial and oblique pencils, but by increasing the separation or
distance between the lenses composing combination B (between the limits,
say, of ✓ (6 to: (/(CD), suitable means, such as a screw, being provided for the
20
purpose, the correction for spherical aberration for the entire combination
or objective is thereby impaired for the moment to any required extent, or
what may be termed diffusion of definition obtained to suit the wishes of the
operator for the time being without at the same time materially deranging
the other necessary corrections of the lens or objective, and this has never
been accomplished heretofore. I observe also that the particulars of
dimensions and proportions given as above are those best suited to accomplish
the particular object in view, but for other objects, such as a combination
possessing greater intensity or rapidity, or one to have less intensity or
rapidity than the combination herein described, other dimensions may be
employed..
The improvements of my leus constructed as above described over existing
double combination portrait lenses are these, viz. :-
1st, capability of adjustment at the will of the operator to obtain for the
moment any desired amount of distribution of definition over several planes,
simply by an alteration in the distance or separation of the elements composing,
as in the lens described, the back combination, without at the same time
deranging the other necessary corrections of the entire objective.
2ud, with the lenses composing the combination at their normal distance
apart more perfect correction of the oblique or marginal pencils for both the
spherical and chromatic aberrations.

page_text: 3rd, greater equality of illumination throughout the entire surface covered
by the lens.
4th, entire freedom from distortion without the aid of diaphragms and
greater flatness of field.
5tlı, greater adaptability to varying purposes of one and the same lens or
combination.
6th, economy as regards the optical means employed.
With the same object of regulating the spherical aberration at pleasure a
combination similarly constructed to the posterior combination in Figure 2
may be made to form part of other lenses or objectives composed of more
than two combinations, such as the triplet; also (but less conveniently) the
regulation of the spherical aberration may be obtained by means of the
anterior combination of a double combination, in which case the anterior
combination is made with the adjacent surfaces of its elements of different
curvatures and with the flint lens outside or towards the view. Means are
provided for slightly altering the distance between these elements at
pleasure.
What I claim as respects this part of my Invention is the construction of
lenses or objectives suitable for photographic purposes, the component parts of
which are of such form and so positioned that by a slight variation of distance
between the lenses of one of the combinations (as by means of a screw
movement) the operator can produce at will any desired amount of spherical
aberration or diffusion of focus without at the same time materially deranging
the other necessary corrections of a photographic lens, substantially as herein
described.
I also claim the combining lenses a, a, b, b¹, substantially as herein
described.
In witness whereof, I, the said John Henry Dallmeyer, have hereunto
set my hand and seal, this Twenty-fifth day of March, in the year of
our Lord One thousand eight hundred and sixty-seven.
J. H. DALLMEYER. (L.S.)