>"Neuman - Ruether" wrote in message
>news:3d39b61d.757547@newsstand.cit.cornell.edu...
>> On Sat, 20 Jul 2002 10:10:12 -0400, "Meryl Arbing"
>> wrote:
>>
>> >Yes, I guess that is my point...testing is only meaningful relative to
>other
>> >tests...to answer the question..Does this particular lens perform better
>> >than another lens in a specific test?

>> Yes - that is why I test. The results tell me if the lens
>> is substandard or not (a simple comparison of the two short
>> edges of subsequent frames, shot at the same wide stop and
>> focus, of the same distant detailed subject, tells me if
>> the lens is optically well-aligned, and if so, it is likely
>> also to be about as sharp as another good sample of the
>> same lens), and how it compares with other similar-FL
>> lenses... In the process of simple alignment, wide vs.
>> middle aperture sharpness, and corner vs. center sharpness
>> testing on film, you can also get info on distortion, flare,
>> etc. by using simple VF tests.
>> (See: www.David-Ruether-Photography.com/slemn.html.)

>> >You may choose to test sharpness or
>> >contrast or flare or distortion and it will be up to you if you decide to
>> >keep a lens that, for example, is really sharp but is prone to severe
>flare.
>> >Perhaps you don't even test for flare or distortion.
>> >Even if you only have some arbitrary personal standard that you hope the
>> >lens lives up to, I still can't see what you do if the lens fails to meet
>> >those standards? Take it back?

>> Of course. Why keep a lens you know is sub-standard, either
>> due to misalignment, or type design?
>>
>> >Then we return to the "cherry picking"
>> >approach of trying (and testing) several lenses before deciding on a
>> >specific individual lens.

>> It is simpler than this - the defective samples are returned
>> until one is found that is sufficiently well-aligned for
>> your standards or purposes (this may take one or two
>> subsequent tries); the poor designs one gives up on
>> immediately, unless they are Ok for your purposes...

>> >Of course, if everybody did that, there would
>> >eventually reach a point when ALL the 'good' lenses would be picked and
>the
>> >stores would be left with the defective stock that they couldn't get rid
>of.
>> >What if that has already happened and all you could hope to buy are the
>> >'substandard' ones...what do you do then? Keep the defective lens? Wait
>> >until a new shipment comes in? (Remember to keep a list of the serial
>> >numbers you have already rejected so you don't waste time re-testing!!)

>> The above, in practice, doesn't happen...

>> >In all, I just think that you are welcome to try out any lens you
>buy...but
>> >don't think that it does anymore than give you some reassurance.

>> Of course! That is the point...;-)

>> >Of course,
>> >you can avoind the whole problem of buyer insecurity by avoiding the
>cheap
>> >3rd party offereings and buying the best that you can afford. I doubt
>that
>> >Leica owners worry too much about getting a lousy lens...Canon 'L' lenses
>> >are probably pretty safe too...same with Zeiss.

>> This is not true - I have seen a bunch of defective Canon
>> and Leitz lenses in my time (and a lower percentage of
>> defective Nikkors...;-). The faith that higher price
>> reduces the defect rate is misplaced...

>> >If you think that you are going to get the performance of a $1000 lens
>for
>> >$100, you are likely to be disappointed more often than surprised.

>> This is true - but it does happen...
>> David Ruether

On Sat, 20 Jul 2002 16:47:13 -0400, "Meryl Arbing" wrote:
>
>What percentage of defective Zeiss or Leica or Nikkor lenses would be
>reasonable to expect? Are we talking... 25% ...or 2%... or .02%? I would
>also expect that the percentage of defective lenses would logically be
>higher in Used examples rather than New ones. So, if a person bought...for
>example...20 used lenses it would be highly unlikely that there would be no
>defects found?

For Nikkors, the range of variation is indicated by
the range in "evaluation numbers" in the list - and if
a particular lens has an unusually high defect rate,
that is covered in the notes with the listing (only a
few Nikkors have a high defect rate [the 35-200 and
35-105MF are about it, though several others show some
variability). With Canon, another photographer in town
had to buy four 20mm f2.8's to get a good one (the others
were quite soft), and his 28mm f2 MF had very noticeable
field curvature (likely a design fault). The Cornell
paper was given a 17mm f4 (Canon marketing...), but it
was dreadful (likely defective...). A 24mm f1.4 Canon AF
appears in my Nikon list (!) since it was so good.
In Leitz, several lenses for the CL I tried were soft at
wide stops, with one 90 f4 terrible, and one really
excellent. Of 21mm's with another Leica user, the first
was poor, the second good. An excellent 35mm f1.4 Leitz
appears in my Nikon list... For Zeiss, I have run across
few defects in the lenses of the several Rollei 3.5E and
Fs that I have owned, though all showed considerable
field-curvature problems (a design problem). A 50mm
Zeiss for the Rollei 66 was soft (probably defective).
Samples and experience too small to quantify (except
for Nikon), but.....
As far as new vs. used, I have seen no differences - the
lenses tend not to become defective with use except for
obvious wear and damage, or oil on the diaphragm. And,
at least with Nikon, the defect rate is very low (new or
used), but the slight misalignment rate is fairly high
(especially in short zooms and CRC retrofocus
wide-angles - particularly the widest), with the same
expectations for new or used... In other words, if you
are particular, test; if not, don't (chances are you
will be OK, except for the few obviously defective lenses,
though you may not have an "optimized" set of lenses
[and may not notice the difference...;-]).
BTW, some specific newer Nikkors are reviewed separately
from www.David-Ruether-Photography.com/slemn.html at:
www.David-Ruether-Photography.com/articles.html, and these include
comments about alignment in the samples tried...