In a message dated 98-07-12 18:52:30 EDT, you (Ingemar Uvhagen) write:
<< If anyone will correct me or ad something, please do. I would be more
than happy know, one cannot get too much knowledge. >>
Well, the problem here is one of translation, not of knowledge. The lens
designers pick whatever glass best fits their design, goals, cost/performance
ratio, etc. There are many type of glass. One of the first of the new
"glass" types was calcium fluorite, which allowed designers to make better
apochromatic telephoto lenses. Apparently there are dozens of types of glass
used in the design of lens, each with its own index of refraction for each of
the wavelengths that film is sensitive to, dispersion index, cost, etc.
After the lens designers do their brilliant work, they turn it over to the
advertising guys. They may not know a Zuiko from a ziggurat but they know
they have to sell by inventing catchy phrases. Various Olympus brochures use
words such as: special optical glass, extra low dispersion glass, high
refractive index glass, apochromatic type elements. Hence the terms UD, ULD,
ED etc. IMHO, just listen here and look at test reports, and this will help
find the best lens.
Good luck in your knowledge quest.
Warren Kato
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