On Sat, 20 Jul 2002 10:10:12 -0400, "Meryl Arbing"
>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...