IMPROVEMENTS IN THE CONSTRUCTION OF COMPOUND LENSES FOR PHOTOGRAPHIC APPARATUS, MORE PARTICULARLY SUITABLE TO PORTRAIT-OBJECTIVES
Year: 1878

page_text: LETTERS PATENT to Gerard Wenzeslaus von Nawrocki, of the Firm of J.
Brandt and G. W. von Nawrocki, Patent Agents, of No. 124, Leipziger Strasse,
Berlin, Germany, for the Invention of "IMPROVEMENTS IN THE CONSTRUCTION
OF COMPOUND LENSES FOR PHOTOGRAPHIC APPARATUS, MORE PARTICULARLY
SUITABLE TO PORTRAIT-OBJECTIVES." A communication from Friedrich
von Voigtländer, of the Firm of Voigtländer and Sohn, of Brunswick,
Germany.
Sealed the 20th May 1879, and dated the 22nd November 1878.
PROVISIONAL SPECIFICATION left by the said Gerard Wenzeslaus von
Nawrocki at the Office of the Commissioners of Patents on the 22nd Novem-
ber 1878.
GERARD WENZESLAUS VON NAWROCKI, of the Firm of J. Brandt and G. W.
von Nawrocki, Patent Agents, of No. 124, Leipziger Strasse, Berlin, Germany.
"IMPROVEMENTS IN THE CONSTRUCTION OF COMPOUND LENSES FOR PHOTOGRAPHIC
APPARATUS, MORE PARTICULARLY SUITABLE TO PORTRAIT OBJECTIVES." [A com-
munication from Friedrich von Voigtländer, of the Firm of Voigtländer and Sohn,
of Brunswick, Germany.]
The first compound lens for photography was, as is well-known, constructed by
the Firm of Voigtländer, in Vienna, in the year 1841, from the calculations of
Professor Petzval, and has served as pattern for all later productions.
It has been variously tried to introduce improvements in the form and position of
the lenses, but the properties of those originally. constructed have not been improved
upon. In order to fully explain the present improvements it is necessary to give
a short description of the said original construction.
The portrait lens as it is consists of two double object glasses with a central stop
and unequal lenses, as shewn at Fig. 1 of the accompanying Drawings. The front
double lense.consists of a biconvex crown glass lense A, and an almost plane-concave
flint glass lense B cemented together by Canada, balsam. At a certain distance
Prine Bd1

page_text: .
from this is the second double object glass of which the first lense C is a flint glass
meniscus while the second is a bi-convex crown glass lense, which are lield apart
from each other by a ring c, c. Between the two double lenses is placed the central
stop b, b, which serves by the introduction of different smaller stops to attain a
greater extension of definition when required.
If the total focal length of both double lenses be taken as F, that of the first
double lense A, B, = f, and that of the second double lense C, D, f', then f: f
3.5 if further be taken a 10 than
=
The distance α =
5.05
The defect of this construction lies in particular in the inequality of the focal
length of two double object glasses A, B, and C, D, which necessarily produce an
incorrect or distorted image, but the defect also arises from the separation of the
two lenses of the back object glass. This arrangement results in a considerablo
absorption of light by partial reflection from the four surfaces of the lenses and has
also a prejudicial effect on the precision of the image.
Now according to the present Invention a combination of lenses is employed
which not only obviates this defect, but also possesses the property of producing
with increased light power a great depth of focus and a greater extension of equal
definition all over the surface; or in other words, it enables larger and deeper
pictures to be obtained by instruments of greater light power than was possible
with the old construction, and the pictures obtained are free from all distortion, so
that straight lined objects are produced without distortion of the marginal lines,
which was also not possible with the existing construction.
These advantages have been attained by altering the proportion of the focal
lengths of the two double lenses in comparison to each other, but in particular by
the alteration of form of the back compound lense C, D, Fig. 2, namely, instead of
consisting of two lenses with unequally curved inner surfaces separated by a
ring, it consists of two lenses whose inner surfaces have the same curvature, and
which can therefore be joined together by a transparent cement like the front.
lenses A, B.
By this means two reflecting surfaces are avoided and therefore the picture
obtained therefrom is of increased intensity and precision.
=
Fig. 2 shews the construction of this improved double object glass.
A and D are the crown glass lenses whose density is 251, and whose index of
refraction is = 1536 B and C are the flint glass lenses, whose density is = 3.21
and whose medium index of refraction n is 1-602. The distance of both com-
pound lenses a is = 5.3. The focal length of the combination A, B, is equal to that
of the second D, C, and their proportion to the total focal length F is as 3 to 2. If F
be taken as 10, then
-
0700

page_text: length of both constructions a form of the lenses and position of the curves similar
to those of the old one; but its focal length is somewhat greater than that of the
object glass A, B, of the old construction. The back double-lense D, C, Fig. 2, has
however a form and position of the radii entirely different from the old construction
and a greatly shortened focal length. For obtaining a more extended picture at
the will of the operator a central stop b, b, is placed between the two double
objectives.
The new construction of the back lense has the further advantage that it can be
adapted to the front lenses of the present construction (after removal of the back
lenses therefrom) so as to produce a new instrument with considerably shortened
focal length, which produces an extraordinary brilliancy of the picture with
increased depth of focus and without any distortion of straight marginal lines.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Gerard Wenzeslaus von Nawrocki in the Great Seal Patent Office
on the 21st May 1879.
GERARD WENZESLAUS VON NAWROCKI, of the Firm of J. Brandt and G. W. von
Nawrocki, Patent Agents, of No. 124, Leipziger Strasse, Berlin, Germany. "Iм-
PROVEMENTS IN THE CONSTRUCTION OF COMPOUND LENSES FOR PHOTOGRAPHIC
APPARATUS, MORE PARTICULARLY SUITABLE TO PORTRAIT OBJECTIVES." A com-
munication from Friedrich von Voigtländer, of the Firm of Voigtländer and Sohu,
of Brunswick, Germany.
The first compound lens for photography was, as is well known, constructed by
the Firm of Voigtländer of Vienna, in the year 1841, from the calculations of
Professor Petzval, and has served as pattern for all later productions.
It has been variously tried to introduce improvements in the form and position
of the lenses, but the properties of those originally constructed have not been
improved upon. In order to fully explain the present improvements, it is necessary
to give a short description of the said original construction. The portrait lens as
it is consists of two double object glasses with a central stop and unequal lenses as
shewn at Fig. 1 of the accompanying Drawings. The front double lens consists of
a bi-convex crown glass lens A, and an almost plane concave flint glass lens B,
cemented together by Canada balsam. At a certain distance from this is the second
double object glass, of which the first lens C is a flint glass meniscus, while the
second D is a bi-convex crown glass lens, which are held apart from each other by
a ring c, c. Between the two double lenses is placed the central stop or screen b, b,
which serves by the intoduction of different smaller stops to attain a greater
extension of definition when required.
If the total focal length of both double lenses be taken as F, that of the first
double lens A, B, = f, and that of the second double lense C, D, = f', then ƒ ƒ'
3:5; if further, F be taken as 10. then
-
==

page_text: of consisting of two lenses with unequally curved inner surfaces separated by a
ring, it consists of two lenses whose inner surfaces have the same curvature and
which can therefore be joined together by a transparent cement like the front
lenses A, B. By this means two reflecting surfaces are avoided and therefore the
picture obtained therefrom is of increased intensity and precision.
-
Fig. 2 shows the construction of this improved double object glass. A and D are
the crown glass lenses whose density is 251, and whose index of refraction n is
=1536; B and C are the flint glass lenses whose density is = 3.21 and whose
medium index of refraction n is =1602. The distance of both compound lenses a
is = 5.3. The focal length of the combination A, B, is equal to that of the
second D, C, and their proportion to the total focal length F is as 3 to 2. If F be
taken as 10 then the radii of the several surfaces 7, 1, &c., are in the following
prapartions..
GERARD WENZESLAUS v. NAWROCKI. (L.S.)