Evolution of the Astronomical Eyepiece - Brayebrook Observatory

EVOLUTION of the ASTRONOMICAL EYEPIECE
The PLÖSSL -
A separate development of the
Ramsden by Gustáv Simon Plössl in
1860 led to a class of orthoscopic,
a c h romatic, wide-field eyepieces,
re f e r red to variously a s the
Symmetrical, the Dial-Sight, and the
Plössl.
The force behind the technical innovations
that enabled Plössl to design this
class of eyepieces in the 1860’s again
lay with the needs of the photographer
and microscopist.
In 1839 he is reported to have made a
Daguerrotype camera and modified the
Chevalier landscape lens. In the year of
his death at the age of 74 the Optical
Society of Vienna named a medal in his
honour.
Plössl’s mo difi cation of Chevalier’s
achromatic doublet anticipated that of
Stein heil and Dallmeyer by almost
quarter of a century.
G.S. Pl össl w as a pprenti ced to
Voigtländer in 1812 when he was 18,
and in 1823 he decided to establish his
own com pany in Vi en na. There he
made microscope objectives, which he
designed himself, and opera glasses. At
the 1830 Scientific Congress in
Heidelberg he received a prize for the
best achromatic microscope.
The first Symmetrical eyepiece consisted
of a matched pair of Plössl’s modified
achromatic and aplanatic doublets, with
their crown bi- co nvex elements facin g
i n w a rds. Th eir separation w as about
0.5Fe, so eye relief was generous (0.8Fe)
and the apparent field about 40˚ at f/6.
Orthoscopy and lateral colour correction
were excellent down to f/4.
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