Improvements in Lenses.
Year: 1897

page_text: Date of Application, 9th Mar., 1897-Accepted, 1st May, 1807
Improvements in Lenses.
I, EDWARD WILLIAMS BARKER of Garretts Road, Upper Darby Township
in the County of Delaware State of Pennsylvania one of the United States of
America Grain Exporter, do hereby declare the nature of this invention and in
what manner the same is to be per ormed to be particularly described and
ascertained in and by the following statement :-
My invention relates to condensing or objective lenses for photographic,
telescopic or mechanical purposes, the object of my invention being to so construct
such lenses that they can be made of any desired size and power, with such a small
expenditure of labour and at such a low cost as to permit of the construction of
much larger and more powerful lenses than it has hitherto been possible to make.
Under the present practice of constructing lenses from glass of the full diameter
of the lens the manufacture of large lenses is very difficult and expensive.
The want of homogeneity in a large mass of glass and the trouble experienced
in properly handling and grinding the glass serve to prevent the manufacture of
lenses of a diameter much in excess of thirty-six inches, and even lenses of this
size can only be made at enormous cost; furthermore, in the ordinary lens there is
considerable loss of light due to the thickness of the glass, and difficulty is
experienced in correcting the spherical aberration of the lens.
I overcome these difficulties by constructing a composite lens, built up from
independent segments, each so shaped and adjusted in respect to the others that all
will have the same focus, the preferable form of lens consisting of concentric rings
each composed of a series of sections, these rings surrounding a central lens which
may be composed of glass of the full diameter of the said central lens or may
consist of a series of segments.
In the accompanying drawings:-
Figure 1 is a diagram shewing in transverse section the sections or segments of
a leus constructed in accordance with my invention;
Figure 2 is a plan of the same;
Figure 3 is a plan, partly in section, and on a larger scale, of part of my
improved composite lens illustrating means which may be employed for supporting
and adjusting the sections or segments of the lens ;
Figure 4 is a longitudinal section on the line 4-4, Figure 3; and Figures 5
to 12, inclusive, are views illustrating modifications and special features of the
invention.
The lens shewn in Figures 1 and 2 is composed of a central plano-convex lens a
and a series of concentric prisinatic lens rings b, d, e, f and g, each of these rings
being composed of a number of segments as shewn in Figure 2, all of the
segments of which the lens is composed being so formed and adjusted as to focus at
the same point.
The central lens, if plano-convex, is a solid generated by the revolution of an
arc of suitable curvature, and its sine, about its versed sinc, and each of the
concentric rings of the lens, if plano-convex, is a solid generated by the revolution
of the transverse are presented by the outer face of the ring, its sine and the
line which for convenience I will call the versed sine, around the central axis of
the composite lens. If the lens be double convex, the same rule is adopted in
forming both the inner and the outer portions of the lens.
The sines and versed siues referred to are preferably the focal sines and focal

page_text: versed sides, although this is not absolutely essential to the proper carrying out OL
my invention.
The segments thus constructed may be properly adjusted to focus while they are
being assembled, and then secured in proper position by any suitable cementing
agent. Special supporting and adjusting means, however, constitute another feature
of my invention, and are hereinafter fully described.
It will be evident that by this method of construction a lens of any desired size
can be made at a rost which is not prohibitive, as the expense due to the difficulties
involved in making large lenses from glass of the full diameter of the lens is
avoided, each of the segments of the composite lens being easily handled, and the
pieces being relatively so small that the glass in each piece can be absolutely
homogeneous. Only a minimum quantity of glass is employed in making the lens,
thus reducing loss of light due to the thickness of the lens, and spherical aberration
can be more effectively corrected than it can be in a single large lens.
The great reduction in the quantity of glass used in making my improved lens,
and the corresponding increase in the light transmitting qualities of the lens, wili
be understood on reference to Figure 1, the plano-convex outline representing the
mass of glass which would be contained in a single plano-convex lens of the same
diameter, while the mass of glass contained in my improved lens, is represented by
the cross-sectional portions.
It is practically impossible in a large single lens to correct spherical aberration
by a proper gradation of curvature from the centre to the circumference, but in
my improved composite lens spherical aberration can be much more readily
corrected by increasing the radius of curvature of ch
receding from the centre, this variation of curvature of the crown glass lenses to
be adopted in conjunction with the use of such achromatic concave flint glass
lenses as may be found upon careful computation and by experience to be best
adapted to the attainment of the end in view.
Spherical aberration may also be corrected by a special adjustment of the
segments of the lens in respect to each other and to the central lens.
The central crown glass lens may be double-convex as shewn in Figure 5 or, in
order to cheapen, or facilitate, the construction of the same, it may consist of two
plano-convex lenses mounted separately, or having their two plane surfaces
cemented together, as shewn in Figure 6, and the segmental lenses may also be
either a segment of a double-convex lens, as shewn in Figure 7, or of two plano-
convex lenses either mounted separately, or cemented together, as shewn in Figure 8,
the convex lens of crown glass being used in connection with the ordinary plano-
concave lens of flint glass, as shewn in each of the figures referrel to.
The central lens, also, instead of being composed of glass of the full diameter of
the lens, may consist of a number of segments, if desired, as shewn in Figure 9,
although the former construction is preferable, as this lens will always be of
comparatively small diameter and hence easily made at small expense. One,
or more, of the small concentric annular lenses may also be in one piece if
desired.
In order to provide for the ready adjustment of each segment of the lens I use
a series of rings i suitably supported in proper position by means of radial bars i
or other appropriate framework, and I provide the central lens as well as cach
of the outer lens segments with clamps m which engage with adjusting screws m
adapted to threaded openings in the rings i, the latter being slotted to permit of
the desired play of the clamps therein in effecting the adjustment of the lens
segments, each segment being preferably provided with three clamps disposed at
the angles of a triangle drawn through the lens segment, such arrangement of the
clamps providing for accurate adjustment of any part of the segment.
The pitch of the inner and outer edges of the lens segments should trend to the
principal focus of the lens, as should also the rings i of the supporting frame.
After the lens segments have been properly adjusted the spaces between the edges
of the same and the supporting frame should be closed by cement or other opaque

page_text: substance, to prevent the admission of light by any other path than through the
lens segments.
The lens segments may, if desired, be adjustable in the clamps by the use of
suitable wedges n, as shewn for instance in Figure 10, or by other suitable means,.
so that in adjusting the lens universal movement of each segment of the lens will
be permissible in order to effect proper focusing.
The construction of adjusting devices shewn in Figures 11, and 12 may, in many
cases, be preferable to that shewn in Figures 3 and 4, as it provides for a more
accurate and universal adjustment at the segments.
In this case, the ring has hollow bosses each carrying an adjusting screw m
which has collars engaging with an inner hollow blocks, the latter having an
arm passing through a slot in the boss s and connected to the clamp m.
Three equidistantly disposed set screws t carried by the boss s act upon the
hollow blocks and provide for any desired lateral, or radial, adjustment of the
same, demanded in properly setting the lens segment.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. A composite lens consisting of a central lens, and a concentric annular lens or
concentric annular lenses, all of the lenses being of the same focus and the inner
face of the concentric annular lens, or of each of the concentric annular lenses,
constituting the sine of its respective portion of the are presented by the outer
convex face of the lens.
2. A composite lens consisting of a central lens, and a concentric annular lens
or concentric annular lenses, all of the lenses being of the same focus, and the
concentric annular lens, or each of the concentric annular lenses being composed of
a number of segments, and having an inner face which constitutes the sine of its .
respective portion of the arc presented by the outer convex face of the lens.
3. A composite lens consisting of independent segmental lenses, so formed as to
have the same focus and combined with means for independently mounting and
adjusting the same.
4. A composite lens consisting of a central lens and a series of concentric annular
lenses composed of segments, in combination with means whereby each segment is
supported and can be adjusted independently of the others.
5. The combination in a lens, of the central lens, a series of concentric annular
lenses composed of sections, supporting rings alternating with the said annular
lens rings, and adjusting screws carried by the said supporting rings and provided
with means for engaging with the lens sections, substantially as hereinbefore
described.
6. The combination in a lens, of the annular lens rings composed of segments,
the intervening annular supporting rings, adjusting screws carrying hollow blocks
which support the segments, and radial screws for laterally adjusting said hollow
blocks, substantially as hereinbefore described.
Deted this Oth day of March 1907
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C.