Hi Winsor:
> I thought the 300/4.5 was built with low dispersion glass which is what APO
> is all about, making all the colors focus in the same place.
Low dispersion glass is not particularily noteworthy or special. It's just a
crown glass that is combined with flint glass (high dispersion) to reduce
chromatic aberration. The 40mm f/2.0 is described as using "low dispersion
glass," for instance. The 300mm f/4.5 is not claimed by Olympus to be
apochromatic. As they put it:
". . . with a combination of high refractive index glass and extraordinary
partial dispersion glass to greatly reduce chromatic aberrations."
An APO lens, by definition, has none AT SOME particular focusing distance.
My take: it's semantic mumbo jumbo that gets us to think there is some special
glass in there. But it isn't ED (extra low dispersion) glass as Nikon calls
it, or as Olympus calls it "special low dispersion" glass.
Gary Reese
Las Vegas, NV
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