Improvements in Photographic Objectives.
Year: 1899

page_text: Improvements in Photographic Objectives.
I, ERNST LEITZ, of Wetzlar, in the German Empire, Manufacturer, 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:-
1
A double lens has been used, in which the crown glass has stronger refractive
power than its attendant flint glass, the crown glass is biconvex and the flint glass
biconcave. This double lens enables a high astigmatic correction to be made, and
this has been recognized and led to a further form of lens, in which astigmatic
sperical and chromatic correction has been so made in each of the triple lenses that
either of the latter can be used alone as a photographic objective.
Experiments have shown that the sperical correction was so far behind with
regard to the importance of the astigmatic correction that objectives in which the
rays falling in an axial plane were brought into conjunction could only be used over
about one third of the theoretical opening. This disadvantage in the lighting power
of the objective is attributable to the fault of astigmatic correction and a subsequent
computation of the rays which do not fall in an axial plane has confirmed this
proposition.
The influence of these unaxial rays which increase with the enlargement of the
opening of the objective, pointed the way to the construction of an objective in
which the number of the astigmatic correction members exceeded that of the
sperical correction members.
Such an objective is illustrated in the annexed drawing;-A and B are two
biconvex lenses turned respectively towards the object and towards the image. The
objective as a whole consists of two unsymmetrical members, of which that marked I
towards the object consists of three parts namely a biconvex lens A, a biconcave
lens Cand a meniscus D. The other member marked II turned towards the image
is a dual combination and consists of the biconvex lens B towards the image and the
less refractive biconcave lens E.
The two biconvex lenses L' L' which are more refractive than the following
biconcave flint lenses give the astigmatic correction. The curve R3 gives the
spherical correction as in the cemented curve of an aplanatic lens. The inuer
member is a meniscus of crown glass of less refractive than that of the flint glass
lens cemented to it.
As this radius is the only means of correction of spherical distortion, neither the
triple nor the dual combination can be used alone, but the combination of the two
must be looked upon as a single system.

page_text: Having now particularly described and ascertained the nature of this said
invention and in what manner the same is to be performed I declare that what I 2
claim 19
A photographic objective corrected for spherical stigmatic and chromatic errors
consisting of two unsymmetrical combinations (I and II) each having on the outside
a biconvex lens (A and B) and inside thereof a biconcave lens (C and E) of smaller
refractive index, and on the inner side of the combination forming the member (I) 2
nearer the object a meniscus (D).
Wah1900
HERBERT HADDAN & Co,
18 Buckingham Street, Strand, London, W.C., Agents to Applicant.