Friends,
I know this might be obvious to some, or even many, on this list, so
please have mercy on me and my lack of knowledge.
First the type of glasses. There are one so called ED glass. I assume it
stands for "Extra Low Dispersion glass", which according to my
dictionary would mean that the light will be concentrated and therefore
give better performance. Right?
Then there are a glass called UD glass. On this I have not find any
information at all, so what does "UD" stand for? I have noticed that
some of the very fast telephoto lenses, like the 350/2.8 and the 250/2
lenses, have this sort of glass. But again, what is it?
For lenses without ED or UD glass, what kind of glass do they have? Just
plain glass?
Then I have a wonder about a thing called Internal Focus. What is that?
(Hmm, I thought all kind of focus was "internal"...) For lenses without
so called "internal focus", what kind of focus do they have?
Once again, I know this might be obvious and perhaps there are
information on this at my local library, but as always: I have not been
there looking (I am ashamed, sob sob...).
I would be very happy if someone could straighten my question marks into
exclamation marks.
--
Regards/
Ingemar Uvhagen
Gislaved, Sweden
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