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 p.3 #10 · Experience wirh Quality Control Issues (Sony, Zeiss, CV) | |
RCicala wrote:
This is a topic that's near and dear to my heart. It's also a topic that suffers, as so many do, but lack of definition. Reality is that Lens copy x may seem absolutely fine to Joe and be absolutely unacceptable to Bill. At last count I've tested somewhere around 40,000 lenses and I'll share what I know.
Out of the box, our failure rate for lenses (pretty high standards) overall is just under 2%. With low variability lenses it's 1%. Lenses we think of as bad are, at most, 5%.
Let's do some quick math. If 2% of lenses fail, that suggests that you would need to, on average, buy 50 copies of a lens to find a truly bad one. So when someone says "I've owned 50 lenses and none of them were bad", I'm not surprised. Half of the people who own 50 lenses should never see a truly bad copy.
What about the guy who has 4 out of 5 bad copies? Very often on the interweb people claim that's BS. It's not. That guy isn't looking for an acceptable copy, he's looking for a near-perfect copy. There are 'as perfect as I can detect' lenses out there, but it's not 98%. On a good, reputable, high quality prime lens it maybe be 65% or 75%. There are most definitely lenses that, by my standards, less than 1 in 10 are perfect. When I see someone who tried 4 copies and all weren't perfect, I'm not surprised - for a lot of lenses I see the same thing in evaluating hundreds of copies. They're mostly acceptable, they're mostly not near-perfect.
So, back to the point, 'acceptable copy' is a very poorly defined term, so when we discuss it, we're often comparing our apples to their oranges and calling it all fruit.
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"Failure rate" is a very subjective term - even if qualified with "pretty high standards".
Most of the lenses I keep I have tried at least 2 copies. The Sony lenses, have had a higher rate of variation than other lenses I have tried, with a higher rate of what I would deem a "failure". The other lenses (Loxias and Voigtlanders come to mind) seem to have more general variation, were some corners are sharper (even if well centered), or varying amounts of slight decentering.
Part of the problem may be the golden copies that often seem to get used for "review". After the review is published people get dissatisfied because their copy doesn't perform to the published standard. There may be some stellar copies of a lens, but many other copies won't live up to it. The other part of the issues is MTF graphs that get published by the manufacturer. Some won't perform to the published MTF graphs. The shortcoming won't be obvious and it would not be easy to label that lens a failure. The CV 15 seems to be an anomaly for Voigtlander, but is a good example of unacceptable vs. failure when it comes to variation. I would call the majority of the bad ones a failure, others may say it is normal variation.
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