On Sun, 21 Jul 2002 17:27:35 +0100, Chris Quayle wrote:

>Neuman - Ruether wrote:
>
>> 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...
>>
>> David Ruether

>Perhaps the basic optical designs of lenses are not be too different in
>terms of quality between manufacturers, since they all have access to
>the same sort of cad packages for lens design.

I have not found this to be true, though it is logical...
Even within a line of lenses, Nikon (for instance) has
produced several quite different optical-design versions
of the 35mm f2.8, and offers even now two completely
different 35mm f2 designs... There are a lot of other
examples in the Nikon line of various designs being offered
for the same FL/speed lens, often concurrently. Between
brands, the differences in designs and performance are
also obvious, and not all 28mm f2.8s, for instance, are
alike, common as this FL and speed is (Nikon has offered
several, ranging from mediocre to excellent, and the best
Nikkor version of the 28mm is generally better than similar
lenses offered by others, even the "fancy-'spensive"
makers...

>What is different is the
>spread of quality, since stuff like selective fitting and testing is
>labour intensive, can't easily be automated and is a fixed manufacturing
>cost.

I'm not sure I agree with this, either...
An indication: most Nikkor zooms shift focus slightly
when zoomed; most "cheap-brand" zooms do not...

>The spread of quality will be greater on a cheap lens for this reason
>and because the manufacturing tolerances are likely more relaxed in any
>case. Plastic lens housings don't help either, since plastics doesn't
>have the dimensional stability of metals.

I agree with the first part, but not the second - plastic
can be a good material for holding tolerances...

>You may get a good example,
>but because of the wider spead, you are perhaps just a likely to get a
>substandard example. Buy from a quality manufacterer doesn't guarantee a
>perfect example either, because there's still a spread, but this is
>likely to be much narrower as the target limits etc will be much
>tighter. I guess this is what you pay extra for...
>
>Chris

With Nikon, at least, the spread in quality is more related
to lens type, and to a very specific few "problem" lenses,
than to an overall manufacturing permitted tolerance...
I suspect the same is true for "off-brand" manufacturers,
with some lenses in their lines being reasonably consistent,
some not...