Improvements in Objectives for Photographic and like purposes.
Year: 1899

page_text: Improvements in Objectives for Photographic and like purposes.
I, PAUL RUDOLPH, Doctor of Philosopby, of Carl-Zeiss-Strasse, at Jena, Grand-
Duchy of Saxe-Weimar, Germany, do hereby declare the nature of this invention to
be as follows:-
The photographic objective hereafter described has been devised for purposes,
which require a large aperture and an anastigmatically flattened field for a compara-
tively large angle. The advantage of this objective, as compared with combinations
hitherto known for similar purposes, for instance the objectives described in Specifica-
tion No. 6028, A.D. 1890 and like anastigmatic constructions, is that the choice of
glasses is hardly limited and less lenses are necessary to obtain good spherical
correction even in types of high aperture.
This double advantage of the new objective is due to the use of two pairs of glass-
surfaces, each pair consisting of two surfaces which face one another, that is to say,
which belong to two consecutive lenses and are separated by an air-space but not
by the diaphragm of the system, and the powers of both pairs being of opposite sign.
be the refractive indices of the two consecutive lenses, r, and r the
If and
121
112
radii of curvature of the glass-surfaces facing one another, the power of such a pair
of surfaces is given by
$1,2
=
111
ri
-
1
+
7'k
the axial thickness of the air-space between both "facing" surfaces being supposed
to be negligible.
There exist already several photographic objectives having two pairs of facing
glass-surfaces separated by air, but the powers of these pairs are both positive or both
negative. It may be inferred from Fig. 3 of Specification No. 27635, A.D. 1896 re-
lating to the so-called Planar, that the two pairs of facing glass-surfaces are the
surfaces, and r, 1 of the lenses L, L, and L, L, respectively. The sign of the
power of each pair is positive. Another construction of this kind has been described
in Specification No. 12859, A.D. 1898. This objective is composed of four separate
parts and contains-according to the data given in M. von Rohr's "Theorie und
Geschichte des photographischen Objectivs" p. 392-two pairs of facing glass-
surfaces, each of which pairs has a negative power.
The effect of combining two pairs of facing surfaces of opposite power is similar to
the result obtained in the objective described in Specification No. 6028, A.D. 1890
by the opposite sign prescribed for the difference between the refractive indices of
the crown and flint-lenses in the cemented components of a doublet. The pairs of
5 facing surfaces produce, in accordance with the signs of their powers, astigmatic
differences of opposite character, so that, in addition to spherical correction of the
whole system and flattening of the image, astigmatism may fully be corrected. In
the former objective the maximum difference of the refractive indices of the lenses
cemented together was (with regard to practical usefulness of the glasses)
In the present objective, however, the difference of the refractive
01-63-150=0.13.

page_text: indices belonging to each of the facing glass-surfaces will amount to 1.50-100=0.50
even in the most unfavourable case. It is further to be considered that when the
present objective has the same number of lenses as the former, its number of elements
available for correction is increased, so that the present objective when consisting of
four lenses presents a surplus of two radii and two air-spaces. From the foregoing
it will be understood that the adoption of the new type of objective will result either
in larger apertures, the spherical corrections remaining of the same quality, or―when
the apertures are unaltered-in improved spherical corrections.
Besides the two pairs of facing glass-surfaces of opposite sign the well-known
means of correction may be employed at will, and in consequence thereof the new
objective may consist of single lenses as well as of cemented lens systems. Moreover
it is an essential feature of the invention, that the selection of kinds of glass is nearly
unlimited, so that glasses which diminish the secondary spectrum may be used,
although their optical properties vary in very narrow limits only.
"
The features of the invention may be realised either in "simple objectives
(objectives having the diaphragm behind or in front of them), or in "doublets"
(objectives in which the diaphragm is placed within the system).
Dated the 20th
L
1000
Improvements in Objectives for Photographic and like purposes.
I, PAUL RUDOLPH, Doctor of Philosophy, of Carl Zeiss-Strasse, Jena, Grand-
Duchy of Saxe-Weimar, Germany, 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:---
The photographic objective hereafter described has been devised for purposes
which require a large aperture and an anastigmatically flattened field for a com-
paratively large angle. The advantage of this objective, as compared with
combinations hitherto known for similar purposes, for instance the objectives
described in Specification No. 6028, A.D. 1890 and like anastigmatic constructions,
is that the choice of glasses is hardly limited and less lenses are necessary to obtain
good spherical correction even in types of high aperture.
This double advantage of the new objective is due to the use of two pairs of glass-
surfaces, each pair consisting of two surfaces which face one another, that is to say,
which belong to two consecutive lenses and are separated by an air-space but not by
the diaphragm of the system, and the powers of both pairs being of opposite sign.
If n₁ and n be the refractive indices of the two consecutive lenses, r, and r the
radii of curvature of the glass-surfaces facing one another, the power of such a pair
of surfaces is given by
$1,2
+
ri
7%
the axial thickness of the air-space between both "facing" surfaces being supposed
to be negligible.
There exist already several photographic objectives having two pairs of facing
glass-surfaces separated by air, but the powers of these pairs are both positive or
both negative. It may be inferred from Fig. 3 of Specification No. 27635, A.D. 1896
relating to the so-called Planar, that the two pairs of facing glass-surfaces are the
surfaces, and 3, r of the lenses L3, 14, and L, L, respectively. The sign of the
power of each pair is positive. Another construction of this kind has been described

page_text: Specification No. 12859, A.D. 1898. This objective is composed of fo01 separate
rts and contains-according to the data given in M. von Rohr's "Theorie und
eschichte des photographischen Objectivs" p. 392-two pairs of facing glass-
rfaces, each of which pairs has a negative power.
The effect of combining two pairs of facing surfaces of opposite power is similar to
e result obtained in the objective described in Specification No. 6028, A.D. 1890
the opposite sign prescribed for the difference between the refractive indices of
e crown and flint-lenses in the cemented components of a doublet. The pairs of
cing surfaces produce, in accordance with the signs of their powers, astigmatic
fferences of opposite character, so that, in addition to spherical correction of the
hole system and flattening of the image, astigmatism may fully be corrected. In
he former objective the maximum difference of the refractive indices of the lenses
emented together was (with regard to practical usefulness of the glasses)
63-1.50 0.13. In the present objective, however, the difference of the refractive
dices belonging to each of the facing glass-surfaces will amount to 1:50-100 =
It is further to be considered that when the
ven in the most unfavourable case.
resent objective has the same number of lenses as the former, its number of elements
vailable for correction is increased, so that the present objective when consisting of
our lenses presents a surplus of two radii and two air-spaces. From the foregoing it
vill he understood that the adoption of the new type of objective will result either in
arger apertures, the spherical corrections remaining of the same quality, or-when
he apertures are unaltered-in improved spherical corrections.
=
= 0.50
Besides the two pairs of facing glass-surfaces of opposite sign the well-known
means of correction may be employed at will, and in consequence thereof the new
objective may consist of single lenses as well as of cemented lens systems. Moreover
it is an essential feature of the invention that the selection of kinds of glass is nearly
unlimited, so that glasses which diminish the secondary spectrum may be used,
although their optical properties vary in very narrow limits only.
The features of the invention may be realised either in "simple objectives
(objectives having the diaphragm behind or in front of them), or in "doublets"
(objectives in which the diaphragm is placed within the system).
In the annexed drawing:
Fig. 1 represents a simple objective constructed according to the invention.
Fig. 2 represents a doublet, one of the two components of which is constructed
according to the invention.
Fig. 3 represents a doublet constructed according to the invention.
Fig. 4 represents another doublet constructed according to the invention.
Fig. 5 represents a third doublet constructed according to the invention.
The most primitive simple objective consists of three single lenses L, L, L, placed
separately as shown in Fig. 1. One pair of facing glass-surfaces is formed by the
surfaces 23 of the lenses L, L₂ and the other by the surfaces 74: 5 of the
lenses I, L. For each of the single elements L₁, L, L, a compound lens or a non-
cemented lens system may be substituted, whereby the construction of the simple
objective becomes more or less complicate.
a component of un-
The most primitive
simple objective con-
It consists of four
Such a simple objective may also advantageously be used as
symmetrical as well as hemi- or holosymmetrical doublets.
kind of an unsymmetrical doublet, a component of which is a
structed according to the invention, is shown in Fig. 2.
lenses I, L, 1, L, the back component Lo+13+1 being the simple objective
But it will be understood that the simple objective may also be
shown in Fig. 1.
used as the front component of the doublet.
The most primitive doublet, which in its totality is constructed according to the
invention, has two leuses in front of the diaphragm and two lenses behind it as
shown in Fig. 3, the two pairs of facing surfaces being placed on different sides of the
5 diaphragm. The surfaces r₂, 3 of the lenses 14, L₂ form the one pair having positive
power, and the surfaces ", " of the lenses Li, L. the other pair having negative
The lenses L, L, L, L, may be single lenses as shown, or compound lenses
power.

page_text: It will be preferable to substitute compounds for some of the single lenses either for
the purpose of remaining within certain limits as to the choice of glasses or for
obtaining certain effects as regards the correction of chromatic or spherical aberrations.
According to the particular purposes of each doublet the elements of such a composite
lens may be made of glasses having the same refraction and different dispersion, or
the same dispersion and different refraction, or different refraction and different
dispersion.
In Fig. 4 a more complicated doublet is shown, which has been developed from the
doublet represented in Fig. 3 by substituting two elements L' and I3 cemented
together for the lens L. Example 3 given below and showing detailed data of
construction refers to the same Fig. 4. In this example L, and L are ground
from glasses having the same refraction but different dispersion, so as to chromatically
correct the whole system.
Finally in Fig. 5 a construction is represented in which for the lens L of Fig. 3
a compound consisting of L, and L has been substituted. In the Example 4 which
gives detailed data of construction in reference to Fig. 5, glasses of different dispersion
and different refraction have been selected by means of which the chromatic
correction as well as the diminution of the spherical zones are obtained.
In the following numerical examples of objectives constructed according to the
invention the letters L₁, L
denote the lenses; d₁, d
their
axial thicknesses; ", "
the radii of curvature of their spherical surfaces;
0₁₂ the distances between the diaphragm and the adjacent lens vertices; ₁, l, the
axial thicknesses of the air-spaces between two lenses (the distances between two
lenses). The radii, thicknesses, diameters and distances are expressed by proportional
numbers, the unity of which is the focal length of the entire objective. By simply
multiplying these numbers with the focal length required in each case, the data of
construction for any objective wanted will be obtained. The different kinds of glass
are determined by their refractive indices ", " and no, relating to the D-line and
the F-line of the solar spectrum and to the Hy-line of the hydrogen spectrum
respectively. The value of
indicates the relative dispersive power of the
no
Δη
1
kind of glass, An being given for the interval between D and Hy, whereas by the

page_text: 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:-
In a spherically and chromatically corrected objective having an anastigmatically
flattened field and consisting of at least three separate lenses, the arrangement that
two air-spaces between the said lenses, none of which air-spaces includes the
diaphragm, are confined one by a pair of glass-surfaces the power of which is positive,
and the other by a pair of glass-surfaces the power of which is negative, essentially
as described.