Improved Photographic Objective.
Year: 1897

page_text: COMPLETE SPECIFICATION.
Improved Photographic Objective.
We, CARL PAUL GOERZ, Optician, 140 Hauptstrasse, Schoeneberg near Berlin
and EMIL VON HOEGI, 14 Durlachstrasse, Wilmersdorf, near Berlin, Optician, both
in the German Empire, 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:i
and by the following statement:-
Our invention relates to an objective for photographic purposes By means of this
objective composed of five lenses astigmatism and spherical distortion is obviated,
and at the same time the strength of the light and sharpness of the impression
are increased whilst the injurious faults occurring in simple lenses and known as
distortion entirely disappear in the direction of the main light rays. For this
purpose experiment has shewn it to be necessary to provide the requisite correcting
elements for the removal of the drawbacks above mentioned by the increase of the i
number of lenses cemented together.
The new objective consists (as shewn in the drawing which illustrates an axial
section) of a series of five lenses united together, which must possess certain special
qualities in order that the object in view may be attained as fully as possible. The
Figures 1, 51; 1, 61; 1,52; 1, 54; and 1, 61; attached to the Figure denote the in-
dices of refraction of the glass used for the separate lenses in round numbers. In order
to obtain the greatest possible strength of light it is proved to be necessary that at
the first refracting concave surface R, as small a refraction (1, 51) as possible should
take place, whilst at the last convex surface R, on the other hand as high (1, 61)
a refraction as possible should be present. Furthermore the first lens must be bi-
concave, so that at the second refracting surface R, there will be a cementing
surface acting as a collector of the light and compensating for the astigmatic
aberration, and in order that this surface be as flat as possible, which is desirable io
prevent curving of the image, it is necessary that at this second refracting surface
as large as possible a difference between the refractive indices of the material of
the first and the second lens be present, that is, that the second lens be constructed
of a glass of high refraction. The second lens must be a bi-convex one, and to
this must be applied a negative lens of low refractive index, so that at the third
refracting surface R, a cementing surface acting as a light collector opposed to the
second one may be formed, which without increasing the astigmatism exercises a
compensating influence upon the distortion which is the product of the other
surfaces, so that by a right choice of the curvature of the surface R, the distortion
for a main ray falling sideways will be completely neutralised. For the compen-
sation of the spherical divergence the surface R, is arranged; at this point there
must not occur a difference in refractive index much greater than 1, 61-1, 54-0,07
because it must have an exactly fixed depth which is determined by the direction
of the principal rays which must encounter it under as small a refractive angle as
possible. because here otherwise the distortion influences would be collected which
can no longer be compensated by the surface R. From this condition, and from
the condition already set forth, namely, that the last lens must be constructed of as

page_text: highly refractive a material as possible it becomes necessary to insert between the
lens and the lens 5 a further positive lens of medium refraction. This lens 4
can be either bi-convex or concavo-convex according as the surface R receives a
positive or a negative curvature. As at this surface on account of the very slight
difference of refractive index (about '0, 02), the errors of distortion and spherical
divergence are very little influenced. The lens may be principally devoted to the
complete removal of the chromatic divergence. With the increase of the number
of lenses in compound cementing systems increases of course the difficulty of
bringing the lenses into the combination in exactly central position, and of main-
taining the same permanently in this position. In order to meet this difficulty
we have arranged in our five lens system that the negative lenses possess a greater
diameter than the positive lenses enclosed by them, and that the said negative lenses
come in contact by means of their projecting exactly centred edges. They con-
sequently enclose completely the positive lenses which can henceforth only have
one position, that is, the exactly correct position in the system.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what we
claim is:-
:-
1. A photographic objective constructed of five cemented lenses, in which a
bi-convex lens of high refraction and a positive (bi-convex, plano-convex, or
concave-convex lens) of medium refraction are cemented between three negative
lenses of which the two first are of very low refractive power, but the last one of the
very highest possible refractive power, for the purpose of removing as fully as
possible (and whilst retaining great strength of light) all the faults of distortion,
especially astigmatic distortion.
2. In the objective characterized in Claim the arrangement whereby the
exactly centred edges of the negative lenses projecting over the positive lenses come
in contact with each other for the purpose of an exact and unalterable centring
of the whole system.
Dated the 5th day of June 1897.
W. P. THOMPSON & Co.,
Of London, Liverpool, Manchester, and Birmingham
Patent Agents for the Applicants.