Improvements in Astigmatic Eye Pieces for Optical Instruments.
Year: 1889

page_text: Date of Application, 13th Aug., 1889-Accepted, 26th Oct., 1889
COMPLETE SPECIFICATION.
[Communicated from abroad by JOSEPH KORNBLUM, Optician, JOHN ALFRED
BRASHEAR, Manufacturer of Instruments of Precision, and PARK PAINTER,
Iron Manufacturer, all of the City of Alleghany, State of Pennsylvania, United
States of America.]
Improvements in Astigmatic Eye Pieces for Optical Instruments.
I, JOHN THOMSON KING of 4 Clayton Square Liverpool in the County of Lancaster
Patent Agent, 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 stateinent :—
My invention is designed to correct in the use of optical instruments the defect
known as astigmatism caused by difference in refraction of the horizontal and vertical
meridians of the observers eye and which more or less completely prevents the
efficient use of such instruments as ordinarily constructed by persons whose eyes (one
or both) have an abnormal difference of curvature of the two meridians of the cornea
of the same eye.
My improvement may be applied to telescopes microscopes
lorguettes opera-glasses, field glasses, levels, and similar instruments but for
convenience I describe it in the specification as applied to an opera glass.
My improvement consists in the application to the eye piece or upper lens of an
opera glass or similar instrument of a secondary lens placed inside of the tube of
the instrument, the character of the secondary lens being such as to correct the effect
of astigmatism of either or both of the human eyes in the use of such instruments.
My improvement further consists in the construction and arrangement of the
parts so that the astigmatic correcting lens may be readily adjusted by the user
to suit the peculiar character of his eye or eyes, and so that in a binocular instrument,
such as an opera glass or a lorgnette, the astigmatic correcting attachment may be
thrown out of use on either or both sides of the instrument, so that it may be equally
adapted to use by a person whose oyes are normal, or by a person one only of whose
eyes is affected with astigmatism.
The secondary lens which I use, instead of being of the ordinary shapes, such as
double convex
or double concave, or plano-convex or plano-concave, has parallel
faces in a section in one direction, and plano-convex shape in a section at right
angles to the first plane of section, or in other words it is a segment of a cylinder.
This lens is made of circular shape and of any desired diameter to suit the instrument,
being usually of about the same diameter as that of the primary lens or eye glass of
the instrument.
In cases where the astigmatism of one or both eyes is merely an abnormal
difference of curvature of the cornea in the two meridians of the eye (the meridians
being at right angles to each other), the problem of constructing an instrument to
cure the defect would be comparatively simple: but as astigmatism of the human
eyes is very frequently not of the regular type, the greatest difference of the
curvature of the cornea occurring in the planes which are not at right angles to
each other, it becomes necessary to a really practical and useful instrument that
the line of the parallel faces of the secondary lens should be adjustable to any desired
angle to the vertical line of the primary lens, and this is very important in a binocular
instrument to accommodate cases of different angles of astigmatism in the two eyes
of the observer.
In order to permit of such adjustment by the user, I have devised a construction
of the eye piece of the instrument such that the astigmatic or secondary lens, either
in an instrument to be used with one eye, or with two eyes may be readily adjusted
to any degree of astigmatism.

page_text: Fig. 1 illustrates my invention as applied to a binocular opera glass or lorgnette,
one half the instrument being shown in section.
Fig. 2 is a plan of the instrument viewed from the eye-piece, showing the
secondary or astigmatic lens turned out from the range of vision.
Fig. 3 is an enlarged sectional view of the primary and secondary eye pieces or
lenses.
Fig. 4 is an enlarged sectional view of the lenses shown in fig. 3, on the line xx
of that figure.
Fig. 5 is a plan view, and fig. 6 a sectional view of the movable secondary lens
holder with the adjustable secondary lens frame and lens in place.
Fig. 7 is a plan view, and fig. 8 is a section of the secondary lens and its frame
detached from the lens holder and from the instrument.
In the several figures like letters indicate similar parts of the apparatus.
In fig. 1 the half of the opera-glass shown in section illustrates my invention.
The construction of the instrument is similar to that ordinarily in use with the
exception of the addition to each half of the instrument of the movable secondary lens
holder for carrying the astigmatic lens, and the construction and arrangement
of the device for permitting of the axial adjustment of that lens. A is the main
tube, at the lower end of which is the object glass. B is the extension tube, arranged
as usual to be extended out or drawn into the main tube for compactness and for
adjustment of the focus. These parts need no particular description. The primary
lens or eye piece a is inserted in a suitable circular cavity in the upper part of the
extension piece B below the screw cap b. To the screw cap b so as to be immediately
above the primary lens, when the. parts are in place, is attached the movable lens
holder by a pivot d, so that the lens holder may be turned so as to bring the
secondary lens in the line of sight, or may he turned out as shown in fig. 2 so as
to be out of the range of vision. A pin or stud k on the periphery of the secondary
lens holder enables the finger of the user to engage it and turn it out when desired.
The lens holder is substantially an annulus as shown in fig. 5, having a recess
around its circular inner edge to receive the frame c carrying the secondary or
astigmatic eye-piece g, which is kept in place by a couple of small screws ii (see
fig. 5). The heads of these screws overlap the outer edge of the light annular frame c
in which the astigmatic lens is set, so as to hold it in its seat without interfering with
its rotation on its axis.
A pin or stud f, projects from the periphery of the frame e by means of which the
astigmatic lens is turned so as to adjust its position relatively to the perpendicular
line of the instrument when used.
In the drawing 1 have shown the auxiliary lens as semi-cylindrical on one face
and plane on the other face. I consider it better however especially in an opera-
glass to employ a lens whose action is negative. In fact, it will always be preferable
to have no magnification in the auxiliary lens.
I have also shown the auxiliary lens mounted with the cylindrical face outside or
next to the eye, and the plane side to the eye glass, but this relative position may
be reversed.
If desired, one surface of the annulus constituting the movable auxiliary lens
holder, may be graduated more or less minutely (as in fig. 5) and then by having
an index on the frame e of the auxiliary lens (the stud may serve as such index)
the degree of astigmatism of the user may be ascertained by adjusting the auxiliary
lens, and the angle being once ascertained, it may thereafter be set without experi-
menting on the adjustment.
When used for opera-glasses in order not to reduce the field, the auxiliary or
semnicylindrical lens may be of the negative or concave form, because the question of
magnification should not be made to depend on the auxiliary lens, but entirely on
the concave eye-glass and the focusing screw, but when used in telescopes or field
glasses, either a positive or cylindrical lens may be used in the same way, but in the

page_text: The
case of using a positive (convex) cylindrical auxiliary lens it should be mounted
quite close to the eye lens in order that the best results may be obtained.
auxiliary lens may preferably be made of light crown glass, and if used as an
astigmatic connection for telescopes should be polished with paper or pitch instead
of felt, at least where high powers are used, which is often necessary in observations
on stars and other celestial phenomena.
By the use of the term semi-cylindrical in the specification and claims, as applied
to the secondary eye piece or lens I do not desire to be understood that the section
of the glass cylinder from which the astigmatic lons is formed is in the line of the
axis of the cylinder, so as to give a lens which shall be actually half a cylinder, but
merely that one side of the lens is a plane surface or may be so, and the other side
curved as hereinbefore described.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed 1 declare that what I
claim is :-
First. The combination with the eye piece or ordinary primary lens of optical
instruments such as hereinbefore set forth of a semi-cylindrical secondary lens,
capable of rotation on its axis within the secondary lens holder; substantially as and
for the purposes described.
Second. The combination with the eye piece or ordinary primary lens of a telescope,
opera-glass, or similar optical instrument of a secondary lens or eye glass of a semi
cylindrical shape, set in a frame or secondary lens holder, so as to be rotateable on
its axis therein, such secondary lens holder being pivotted to the instrument to
permit the secondary lens being turned in or out of the line of vision; substantially
as described.
Third. In a binocular telescope, lorgnette or opera glass the combination with the
ordinary object glass and eye-glass at each end of the instrument, of a sumi
cylindrical lens set near to and substantially parallel with the eye glass and set
in a circular frame capable of rotation on its axis in an annular frame or auxiliary
lens holder, which is pivotted to the frame of the instrument so as to be readily
turned into or out of the line of vision of the instrument, as and for the purposes
described.
Fourth. In combination with eye and object glasses of a telescope or similar
optical instrument and the frame carrying the same, an annular lens holder for
carrying a secondary astigmatic lens, within which frame the said lens is capable of
being turned on its axis, and a graduated scale for indicating the angle of
astigmatism when the primary and secondary lenses are adjusted in use, substantially
as described.
1
1000
Per pro J. T. KING,
J. Johnson.