文档介绍：Chapter
The Cooke Triplet and Tessar Lenses
(Entire contents Copyright ° c 1998 by Gregory Hallock Smith, All Rights Reserved)
Following the introduction of photography in 1839, the development of camera
lenses progressed in an evolutionary way with occasional revolutions. Almost im-
mediately, the singlet meniscus Landscape lens was achromatized, thus ing
a cemented doublet meniscus. Soon afterward, pairs of either singlet or doublet
menisci bined symmetrically about a stop. The most essful of the
double-doublets was the Rapid Rectilinear lens, introduced in 1866. This use of
symmetry was then further extended to pairs of menisci, with each meniscus con-
sisting of three, four, or even ¯ve elements cemented together. The most essful
of these lenses was the Dagor, a double-triplet (six elements), introduced in 1892.
The Dagor and some of its variants are still in use today.
The ¯rst revolution or major innovation occurred in 1840 by Joseph Petzval
with his introduction of mathematically designed lenses. Petzval's most famous
lens is the Petzval Portrait lens. The Petzval lens is not symmetrical and has major
aberrations o®-axis (most noticeably, ¯eld curvature). Nevertheless, in 1840 it was
an immediate ess, not least because at f / it was 20 times faster (transmitted
20 times more light) than the f /16 Landscape lens, its petition at the time.
Petzval type lenses were widely used until well into the twentieth century, and they
are sometimes still encountered, especially in projectors.
The second revolution, which began in 1886, was the development of new types
of optical glass, especially the high-index crowns. These glasses made possible the
¯rst anastigmatic lenses; that is, lenses with astigmatism corrected on a °at ¯eld.
The third revolution was the invention by H. Dennis Taylor in 1893 of the Cooke
Triplet lens (Cooke was Taylor's employer). A Cooke Triplet consists of two positive
singlet elements and one negative singlet