: ===================
: We went through this before. The Zuiko 300/4.5 does not have ED glass.
: Please see FAQ page at: http://brashear.phys.appstate.edu/lhawkins/
: at section L2.
: ===================
:
: It may or may not. I've discussed this with folks at Olympus USA tech
: support and at different times have been told conflicting information
: about whether the 300/4.5 used any low dispersion elements.
For what it's worth, here is how the glass of the 300/4.5 is described in The OM
System Lens Handbook:
"The front of the lens features a luxurious 4-elements in 3-groups construction,
with a combination of high refractive index glass and extraordinary partial
dispersion glass to greatly reduce chromatic aberrations."
Extraordinary Partial Dispersion? EPD? Hmm, it almost seems that, to use
Olympus'
words, this lens "unfortunately has a very high quality"... ;)
I doubt, however, that this is the same as Extraordinary (Low) Dispersion (ED).
But still they don't use this term EPD for the 400mm and 600mm Zuikos, so that
makes the 300/4.5 special.
Here is how the glass of the 350/2.8 is described:
"The provision of two lens elements of special low dispersion glass, and another
of extraordinary partial dispersion glass successfully cuts chromatic
aberrations
to virtual insignificant proportions."
Special Low Dispersion - SD, and again, Extraordinary Partial Dispersion.
The 250/2:
"Chromatic aberrations are completely corrected by the use of special low
dispersion glass, and extraordinary partial dispersion glass for each of the
four
front elements."
The 180/2:
"Color aberration is corrected virtually to perfection thanks to the utilization
of newly developed optical glass with special low dispersion and abnormal
dispersion characteristics."
The 24/3.5 Shift:
"The front lens element is made of special low diffusion glass to reduce
chromatic
difference of magnification and upgrade performance at the image periphery."
The 1000mm/F11:
"The apochromat type front lens group provides minimal chromatic aberration, so
both resolution and contrast in this lens are outstanding. The special lens
configuration features two varieties of flint glass and makes use of the tiny
difference in their refractive indices to correct for colour aberrations. This
combination is known as Schubel, Flint Apo and makes an important contribution
to
upgrading the lens performance."
So the 1000mm is also something special; although the terms SD, ED or EPD aren't
used, here we see the term APO which (I think) describes a lens using special
glass.
The 35-80/2.8, from a Dutch OM-3Ti brochure:
"Dankzij het gebruik..." oops, I better translate it ;) "Thanks to using glass
elements of extra low dispersion (ED) and elements with a high refractive index
the qualities of this zoom can be compared with those of various lenses of
single
focal length."
And finally it's worth mentioning that the 35-180/4.5~5.6 lens of the iS-3000
and
the 35-135/4.5~5.6 lens of the iS-1000 and iS-2000 feature an Extraordinary
Dispersion (ED) element.
So Olympus seems to use both the term SD (also used by Tokina) and ED (which is
a
Nikon term). O well, at least they don't use the terms AD (Minolta) or UD
(Canon).
H@nz
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