Well, this depends on whether you are looking at lenses actually
named Plasmat or lenses of the Plasmat type. The original Plasmat was
designed by Paul Rudolph, who is also the designer of the Tessar and
Protar lenses. He designed the Plasmat in his later years after being
forced out of retirement by the extreme economic depression in Germany
following WW-1. He chose to work for Hugo Meyer, a relatively small
company, rather than go back to Zeiss, where he had done all his early
work. The Plasmat was one of the designs he produced for Meyer. While
Rudolph's original Plasmat was not a particularly good lens the
generic type is capable of outstanding performance and has become the
basis of nearly all modern large format camera lenses and nearly all
enlarging lenses for all formats.
   The Plasmat is derived from the Dagor by air-spacing the inner
elements, which are cemented in the Dagor. This results in giving the
lens designer some additional degrees of freedom, namely two surfaces,
a spacing, and a thickness, to work with. The Plasmat, in comparison
to the Dagor and other similar cemented meniscus lenses, has very much
less spherical aberration, especially the zonal spherical that results
in the focus shift typical of the Dagor. The Plasmat is also capble of
excellent correction for astigmatism. It has nearly as wide an angle
of coverage as a Dagor despite the better performance.
  Despite these advantages the Plasmat type was not popular with
designers until after good lens coatings became available. A Plasmat
has eight glass-air surfaces, compared to four for a Dagor, so it has
a tendency toward excessive flare unless coated. Since the development
of economical and rugged coatings the Plasmat has come into its own
and such lenses are now very common.
   One reason old Plamats, I mean those made by Meyer, are expensive
is probably because they are rare, not many having been made. Some
recent Plasmat _types_ are expensive simply because they are modern
and rather expensive lenses. However, its easy enough to find middle
aged lensess of this type like the Schneider Symmar camera lenses and
Componon enlarging lenses, which are quite cheap on the used market.
  The Makro-Plasmat was one of the early examples of this type and is
probably now a collector's item.

Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com