IMPROVEMENTS IN COMPOUND LENSES WHERE ACHROMATISM IS DESIRED
Year: 1878

page_text: PROVISIONAL SPECIFICATION left by Edmund Manasseh Tomlinson
Tydeman at the Office of the Commissioners of Patents on the 15th April
1878.
EDMUND MANASSEH TOMLINSON TYDEMAN, of Liverpool, in the County of
Lancaster. "IMPROVEMENTS IN COMPOUND LENSES WHERE ACHROMATISM IS
DESIRED."
My Invention consists of improvements in the construction of compound
achromatic lenses suitable for use in telescopes, microscopes, and other optical
instruments, and is intended more completely to eliminate the secondary or out-
standing spectrum of such lenses, and to render them more perfectly achromatic.
It consists in forming such lenses, which may be double, triple, or multiple, not as
hitherto by the union of lenses made of different kinds or species of glass or other
refractive media, but of one kind or species of glass or other suitable refracting
substance, only yet of different densities and refractive powers.
Achromatic lenses have been constructed by combining lenses made of several
different kinds of glass or other refractive substances of different densities or refractive
powers; for instance, there have been combinations of flint and crown glass, of
flint, crown, and pane glass, of crown or plate glass with some other more refractive
substance to form achromatic lenses; but owing to the large irrationality or irre-
gularity, or want of correspondence between the coloured spaces in the various
spectra formed by the refraction of light through such substances of different species
or kinds there is generally a considerable amount of secondary colour left uncor-
rected or outstanding in the images of objects formed by the rays of light passing
through such lenses, whereas in glass or other material of one kind or species,
although of different densities and refractive powers, the irrationality or unequal
refraction of the coloured rays is not so great. I therefore construct my improved
achromatic lenses with two or more glasses made from material of the same kind or
species of glass (such as that known as flint glass, which is capable of being made of
varying density), but of different densities or refractive indices; and I also use
Bint glass lenses in lieu of the usual crown or plate glass lenses in achromatic object
lenses and object glasses.

page_text: For a microscope object glass, often composed of two or more approximately achro-
matic lenses, or set of lenses, either in contact or nearly in contact with each other, Isome-
times make one of the several sets of compound lenses composing such object glasses
of one refracting medium, such as flint glass, and the other set or sets or single
lenses of a different refracting medium or media; or I use single lenses of crown, or
flint, or any other suitable substance in combination, though not necessarily in
contact with an achromatic set composed wholly of flint glass or any other suitable
refracting substance. I therefore employ glass or other suitable substance of one
kind only, but of different densities or refractive indices for the formation of (so-
called) achromatic lenses, or sets of lenses, and in the object glasses or other parts of
telescopes and other optical instruments; also in the formation of the individual
compound lenses used in the combinations called achromatic object glassos for
microscopes, dialyte telescopes, cameras, magic lanterns, and other optical instru-
ments, and I do not confine myself to any particular form or focus for such lenses,
which admit of an almost infinite variety.