Evolution of the Astronomical Eyepiece - Brayebrook Observatory

EVOLUTION of the ASTRONOMICAL EYEPIECE
In the mid 1880’s Dr. Hugo Schroeder
produced a high power design of triplet
with a wider, flatter field, suited to
micr ometric work because of the comparatively
large distance between the
lens’ first surface and the web. The
triplet lens was composed of a dense
flint plano-convex between two lenses
of soft crown. The aperture of the lens
could be half its focal length without
any sensible defect in angular magnification
or rectilinear distortion.
In 1890 Er nst Abbé and Paul Rudolph
tur ned their attention from microscope
to photographic objectives. They felt
their work on what Abbé had come to
term ‘apochromatic’ lenses could have
a useful application in the field of photography.
Their initial lens consisted of
a thick cemented triplet in the middle
of an existing symmetrical lens called
the Periscopic. A German patent was
taken out on behalf of Zeiss by
Rudolph in 1911, registering their
triplet design . Zei ss marketed th is
Monocentric variant in several forms
until the mid-1950’s.
There are two other designs of cemented
triplet; the HASTINGS LOUPE and
the assymetric LOUPE TRIPLET - both
developed in the 1910’s. They are still
the most common form of achromatic,
wide-angle, hand magnifier.
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