[Leica] Lens tests and sample variation

[Mike Johnston <michaeljohnston@ameritech.net>]

>>>On the other hand, don't get too wrapped up in the magical
reliability of any lens test method, or lens tester.  Regardless of what
a
great job they did, they didn't test the lenses they didn't test.  There
is an
manufacturing tolerance for even Leica lenses. How do we
know where  a tested lens fits into those tolerances ?   At the high
end?  in
the middle?  or at the low end ?<<<

Stephen,
And let's not forget that any "test" is a shortcut--the best way to get
to know a lens is to use it over an extended period of time and
carefully and intelligently appraise results. It's amazing to me how
much weight people give to tests, and how little weight they are willing
to give, generally, to experience. I have photographers contact me all
the time who admit that they have never liked a lens they've used for
years, but they continue to use it because it got a good test report. Or
the opposite, that they have a lens that they really love because it
performs wonderfully for them, but they guess it's not a good lens
because it didn't earn favorable marks on some test.

And my favorite--people contacting me to ask for an evaluation of a lens
they already own. Silliness!


>>>The ideal testing
situation may be to test a large enough sample lenses to reasonably be
sure
what the average performance really  is.  I don't put much
trust in a test of ONE lens.   Increase the sample to 25 to 50 lenses in

different serial number batches, and I would be inclined to
believe the average results.   Another  lens testing problem is the
source of
the lenses.  Is the lens a random off the shelf purchase,
or specially selected through the manufacturer and distributor?<<<

My son's "Uncle" Arthur Kramer, when testing lenses for _Modern
Photography_, would receive lenses from the manufacturer that would test
spectacularly well. When he asked, he was told that they were regular
production samples. So he would reply that if this was so, he would buy
this lens and keep it. And the manufacturers would say, no, no! Send
that lens back and we'll send you a new one! And he'd say, no, this one
is fine, I'll keep this one. There was really nothing they could say
without admitting that the lens had been carefully cherry-picked for the
test. As Arthur said, he got a lot of awfully nice lenses that way. <s>

I only ever got sent one cherry-picked lens, and it was a beauty. I
tried two other samples of the same lens bought off the shelf, and they
were very good--but not quite _as_ good.

- --Mike