Year: 1888

page_text: We Dr. HEINRICH LUDWIG HUGO SCHRÖDER of 5 The Terrace Clapham Common
in the County of Surrey Optician and JOHN STUART of The Hollies Clapham Common
aforesaid Optician do hereby declare the nature of this invention to be as follows :—
This Invention relates to a new and improved lens or lenses designed for use where
it is desirable to obtain plain images of large fields of view which shall be sharply
defined up
to the margin as for example is the case in photography.
According to my invention I combine two simple or uncorrected lenses of which
the outer lens is plano-convex and is composed of a glass of high refractive index
and low dispersive power the inner lens being plano-concave and being composed of a
glass of lower refractive index but of the same or preferably of higher dispersive
power.
The two lenses have their plane surfaces opposed to each other and are preferably
cemented together the two curved surfaces being portions of concentric spheres.
By proper choice of the radii of these spherical surfaces and of the glasses used and
of their thickness a corrected lens can be made to have a positive focus i.e. that is one
to give a real image of an object receivable on a screen and the corrections of
curvature and colour in such image may be made very perfect throughout a consider-
able angular distance from the axis. The ratio of the radii of the two concentric
spherical surfaces will depend upon the refractive indices and dispersive powers of
the glasses used.
The herein before described arrangement may be slightly departed from either by
the two external surfaces not being precisely concentric or the two internal surfaces
precisely plane without departing from the substance of this invention but the best
results will be obtained in the manner above described.
Corrected lenses made as above described may of course be used also as
combinations.
This 7th CA 1000

page_text: Improvements in Lenses.
We, Dr. HEINRICH LUDWIG HUGO SOHRÖDER of 17 Althorp Road, Upper Tooting
in the County of Surrey Optician and JOHN STUART of The Hollies, Clapham in the
County of Surrey Gentleman 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 :-
This Invention has for its object to provide a lens in which the errors of curvature
of the image and colour correction incident to other lenses are overcome and this
over a large field of view. Lenses made according to this Invention give a sharply
defined image throughout the field which is of great advantage in most or all
applications of lenses and especially so for photographic and other like purposes.
Hitherto all achromatic lenses (having either flat or other contact surfaces,
that give a positive image have the convex radius shorter than the concave radius.
Now the distinctive feature of the lens according to this Invention is that by
employing glasses combined as hereinafter described the radius of the convex surface
is enabled to be longer than that of the concave surface and at the same time a
positive image is still obtained. The convex and concave surfaces may thus be
arranged to represent parts of two concentric spheres.
According to this Invention the objective is composed of a convexo plano lens
made of glass of a high refractive power and relatively low dispersive power combined
with a plano concavo lens made of a glass of lower refractive power than that of the
glass of the convexo plano lens but of the same or higher dispersive power than that of
the glass of the said convexo-plano lens. The inner or contact surfaces of these two
lenses are placed together and preferably cemented the convexo plano lens forming
the front portion of the objective.
By proper choice of the radii of the spherical surfaces of the lenses and of the
glasses used and of their thicknesses an aplanatic lens can be made having a positive
focus that is a lens giving a real image of an object receivable on a screen and having
great flatness of field and suitable colour correction throughout a considerable augular
distance from the axis. The ratio of the radii of the two concentric spherical surfaces
will depend upon the refractive powers and dispersive powers of the glasses used as
hereinafter more fully explained.
And in order that our said Invention may be fully understood we shall now proceed
more particularly to describe the same and for that purpose shall refer to the several
figures on the annexed sheet of drawings the same letters of reference indicating
corresponding parts in both the figures.
Figure 1 of the accompanying Drawings is a transverse section of an objective made
according to this Invention a being the convexo-plano lens of high refractive and low
dispersive power and 6 being the plano concavo lens of lower refractive power and
the same or higher dispersive power. The convex and concave external surfaces
(marked respectively e and d) are portions of concentric or approximately concentric
spheres having their centre at and the plane internal surfaces are preferably
cemented together at c.

page_text: In order to obtain a plane image throughout a large field of view the radii of the
external surfaces (e and d) should have a certain ratio to each other dependant on the
refractive and dispersive powers of the glasses used.
In practice it is found that the limits of the refractive powers of glass available for
the front lenses of the improved objective are from about 1.59 to 161 the index being
taken to be corresponding to the D line of the spectrum. Similarly the range of
refractive powers for the glasses available for the back lens of the said objective ranges
from about 1.50 to 1-53 the refractive index being as before that for the D line of the
spectrum. It is to be understood that these figures are given as being what are
considered the best with glass as now generally obtainable.
With the before named glasses the ratio of the refractive and dispersive powers
which would produce the best radii so far as flatness of field and suitable colour
correction of the image are concerned is given by the following tables.

page_text: Thus for example if the front or convexo-plano lens a have a refractive power of 1.61
for the line I) in the spectrum and the back or plano concavo lens have a refractive
power for the same line of 1.50 the ratio of the curves of the two spherical surfaces of
the lenses (e and d) should be 1-138 in order that throughout the field of view the
image may be plane with suitable colour correction.
Slight deviations may be made from the directions given above as for example by
slightly departing from the plane internal surfaces (c) or from the concentricity of the
external spherical surfaces (e and d) or from the ratio of the radii or dispersive and
refractive powers of the two glasses (a and b) given by the above tables without
departing from this Invention but we believe that by following the rules given above
the best results will be obtained with glass at present obtainable.
With the aid of these tables the requisite ratios of the dispersive power appertaining
to the refractive powers of the glasses used and also the requisite ratios of the radii
of the lenses may be calculated by the ordinary method of interpolation. The
objectives may be used singly as in Figure 1 or combined as in Figure 2 (g being the
diaphragm between them).
Having now particularly described and ascertained the nature of our said Inven-
tion and in what manner the same is to be performed we declare that what we
claim is.
1. The combination of a convexo plano lens made of glass of high refractive power
and relatively low dispersive power with a plano concavo lens made of glass of lower
refractive power and the same or higher dispersive power (the said lenses having plane
or slightly curved contact surfaces and outer concentric or approximately concentric
surfaces) to form an aplanatic lens or objective giving a positive image substantially
as herein before described with reference to the accompanying drawings.
2. The improved lens or objective herein before described.
D