Improvements in Photographic Objectives.
Year: 1899

page_text: Date of Application, 8th Feb., 1899-Accepted, 1st Apr., 1899
COMPLETE SPECIFICATION.
Improvements in Photographic Objectives.
We, CARL PAUL GOERZ and EMIL VON HOEGH, both of Rheinstrasse 45/40,
Berlin-Friedenau, in the Empire of Germany, Manufacturers of Optical Instru-
ments, 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:-
Photographic objectives have been previously constructed consisting of three.
lenses, in which spherical and stigmatic distortions are corrected by each two
lenses following one another and cemented together containing a dividing plane
giving a light dispersion and one for light concentration.
Figs. 1 and 2 show the arrangement of such objectives in axial section. In-
both objectives a lens of medium refraction is enclosed between a lens of smaller
and one of greater refracting power. In the form of Fig. 1 the enclosed lens
has a negative, the enclosing lenses a positive focal distance, in the form of Fig. 2
the enclosed lens has a positive and the two others a negative focal distance.
In both cases by the light dispersing cemented plane Z means is given for
compensation of the spherical deviation and by the light concentrating plane S
means for correcting stigmatical deviation.
The operative opening, which can be given to systems of this kind, and thereby
the illuminating power of the objective, is dependent upon the size of the
difference between the refractive indices of the kinds of glass meeting at the
cement planes because the smaller these differences, the deeper curves the cemented
planes must have to compensate for the before mentioned faults; but the curvature
of these curves must not surpass a certain admissable amount otherwise the
distinctness of the picture received by the objective would be destroyed. The
refracting indices of those kinds of glass which can be used for such objectives,
lie within the values 151 and 1'61 and hence the middle glass has a refractive
index between these limits the differences of the refractive indices can on the
average therefore not exceed 0.05.
In order to have a greater illuminating power without augmenting the number
of the lenses and while preserving the distinctness of the picture and the
correction of all faults, we do not use as in the above mentioned objectives a
light dispersing cement plane but this correction is attained by the lenses at
the place Z receiving not the same but different radii of curvature so that the
curve of the negative lens is greater than that of the positive lens and no that
between both now distanced lenses an air space of the form of a positive meniscus
is formed. In consequence of this arrangement it is no longer required that for
correcting spherical deviation the negative lens should have greater
refractive index than the positive one or, what is the same, that the
enclosed lens should be made of a glass of a medium refraction, but one can in
this case make the middle lens when it is a biconcave negative one (Fig. 3) of
very low refracting glass, or, if it is (Fig. 4) a biconcave positive lens of a glass
as strongly refractive as possible. The direct consequence of this is, that in both
cases at the light concentrating cement plane S two species of glass of very

page_text: great difference of refractive index meet together and that consequently this
plane compensates for stigmatic deviation with notably less curvature than was
formerly possible.
An advantage of this new arrangement of the lenses which is not less important
than the augmented light power and distinctness of the picture is that with it,
it is also possible to meet the so called requirement of sine in every single system
to the fullest extent that is to say, it is possible to take also into account the
distinctness of the picture obtained by the single system itself of oblique falling
pencils of rays while using the full objective opening by the possibility of
annuling the coma in a certain direction of the chief ray, which was not possible
with cemented three lens systems in which other faults have been completely
compensated.
The numbers inscribed on the drawings give the coefficients of the kind of glass
used for the respective lenses. The cemented plane S concentrates the light,
the plane Z disperses the rays.
It is clear without further explanation that one can put together two of the
described lens systems and can use them as a compound objective. .-
די די
Having now particularly.described and ascertained the nature of this
invention and in what manner the same is to be performed we declare that what
we claim is:-
1. A three lens system for photographic purposes formed by a cemented meniscus
of two lenses, one biconcave lens of lower and one biconvex lens of higher.
refraction in conjunction with
(a) Either a meniscus of positive focal distance put in front
(b) Or a meniscus of negative focal distance put behind.
wherein the surfaces lying one opposite one another have such curvatures that
between the single and the cemented meniscus an air space in the form of a
positive meniscus is formed.
2. A compound or double objective formed of two lens systems as in Claim 1.
Dated this 8th day of February 1899.