I am sure you know the history of the Heliar. One interesting
variation is covered in a patent by Fred Altman of Kodak, USP No.
2279384 Altman states his objective (no pun intended) was to reduce
astigmatism and zonal spherical aberration. Included are several
references to the patents for prior art. Kodak exploited this patent for
its Ektar 50mm and 75mm enlarging lenses and a number of camera lenses
including some lenses for the Kodak Ektra camera, the lens for the Kodak
Medalist, and the 105mm, f/3.7 Ektar for small press cameras. Some of
these were among the first coated lenses available. They have a
reputation for being exceptionally sharp. The Ektar series lenses were
exceptionally well color corrected, especially for lateral color, and
were meant to encourage the use of color film. The large format Kodak
Commercial Ektar is very nearly apochromatic. I think the Voigtlander
Apo Lanthar is also a Heliar variation using rare earth glass for one or
more elements. Actually, Kodak pioneered in the manufacture and use of
rare earth glasses using lanthanum glass in a number of lenses. Note
that thorium was also used in some glass but is radio-active enough to
cause the glass to turn brown with time. Lanthanum is not radio-active
but many lenses used a combination of the two.
--
Richard Knoppow
dickburk@xxxxxxxxxxxxx
WB6KBL
