[none]

[msmall@roanoke.infi.net]

>--this old saw about all lenses being better if they don't have to clear
>the mirror box is an old wives' tale--if you'll think about it for a minute,
>_all_ point-and-shoots have lenses that don't have to clear a mirror box. A
>good lens is a good lens and a bad lens is a bad lens and broad
generalizations
>like this simply don't hold across the board. (Third commandment of
>photography--never believe marketers' hype.) 

Well, you are wrong.  It is an optical fact, not marketer's hype, that a
retrofocus lens is harder to design to perform identically with a
non-retrofocus lens.  By requiring the lens be retrofocus, as SLR's do, is
an additional parameter the optical designer has to work around.

Which isn't to say that a good designer can't make a retrofocus lens
perform as well as a non-retrofocus lens but, to do so, he or she must make
a lens which is going to cost more to produce.  It is a simple fact of
optical engineering that it is easier to design a good non-retrofocus lens
than a retrofocus one.

AND HE ALSO SAID:

>Early Summitars and Elmars and so forth had quite soft glass in the objective
>(front element) and were susceptible to "cleaning marks" from excessive
>(regular) cleaning (which is not necessary--there's no earthly reason to
clean
>your lenses more than once a month in the absence of visible soiling). So
Leica
>began in the 1970s to incoporate an objective made of harder glass as one of
>their design goals.

This simply isn't true.  Leitz lenses from the '40's and '50's have soft
coatings, but not soft glass.  As someone pointed out, the cleaning marks
complained of are rare on uncoated lenses, common on early coated lenses,
then become rare on later coated lenses.  The glass in many of these
designs, such as the 4/90 Elmar, is identical.

What changed was Leitz' switching to a vacuum-depositing technique for
coating lenses once the Zeiss patent on this had expired, as this leaves a
much more durable coating.

Marc


msmall@roanoke.infi.net  FAX:  +540/343-7315
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