In article <01bc8248$fee70360$a7e0f7c8@romulan>, dia@nutecnet.com.br says...

>Can anyone tell me how much of a difference there
>is in a SIgma or Tamron lens versus Nikon or
>Minolta? For a serious ametuer with hopes of
>turning pro.
>Thanks.
>Marie

You may want to visit my infamous "SUBJECTIVE Lens
Evaluations (Mostly Nikkors)" for a recounting of
my (biased) experience...;-) It can be found on
my web page at: http://www.fcinet.com/ruether
under "Ritingz" or "I babble...", then under
the title above... The short of it: the Nikkor
line is very consistent in quality throughout,
with few exceptions - this is not true of
most other lines, though some good lenses can
be found in most lens lines (but with Nikkors,
less "cherry-picking" is necessary, resulting
in a wider selection of available fine lenses).
Hope This Helps, aka David Ruether...