In article <495t1p$gl3@news.sas.ab.ca>, dhall@freenet.edmonton.ab.ca says...
>Gary Hunt (glh@srv.net) wrote:
>: >moreover, many photo rags do not report how many samples theytested.
>: > what you really want is the number tested, the average, and the
>: > variability. how uniform the quality of the lens is also important.
>
>SO - what might be expected in terms of variability? I expect that the
>robot-controlled mass production has pretty small tolerances, & that
>quality control is pretty good. Therefore, I assume that consistency is
>high, and that variability within a particular lens model is a *non* >issue to the consumer.

In my experience and in that of friends, variability is a BIG issue.
Nikon lens manufacturing is pretty consistent (see "SUBJECTIVE Lens
Evaluations [Mostly Nikkors]" [seek "NIKON"] at: http://www.phys.rug.nl/mk/people/aue/photo.html
for examples of experience with multiple samples), but a couple of lenses in the line are variable in sample-to-sample quality (the MF 35-105mm stands out - only 2 in 10 that I tried were well-aligned).
Other lens lines show MUCH greater variation, even a scary level of
variation (to the point that I would not consider buying lenses in
those lines without testing and selecting every lens).

>Does anybody have any data on this issue? Should consumers "shop >around" and test several different copies of the same lens to choose >the sharpest one?

Yes! If you care about lens quality - BUT, beware of developing an
obsession! (When you begin to realize just how high a percentage of
some lens lines are defective in manufacturing - and it doesn't
matter whether the country of origin is Japan or Germany - it is hard to buy without testing everything!)

>Please note that the issue is not simply Brand A vs Brand B,
>but consistency of the same lens within the same brand.

There may be some association, or it may be incidental, but the Nikon
lens line is also remarkably consistent in the quality of lens design
throughout the line regardless of price (lens barrel quality is another matter....)
Hope this helps.