Originally posted by aldo taddia Thank you for your comforting words! I thought I was the one who had always been lucky to buy my lenses.
I was worried about a possible new purchase of the 21mm f.2.4, having read the bad reviews in a review of this lens, then corrected in excellent, having replaced the defective copy with a fully functional one.
It seemed that one in two copies was with badly centered lenses or with other defects and that you had to check it and then have to send it back .
You have to be wary when reading negative reports of lenses, and careful when drawing conclusions from them. Just because someone had what
they consider to be a defective lens, doesn't mean you or I would have considered it so. Some folks have
impossibly high standards. Then, just because they had a supposedly defective lens and the replacement was better, doesn't mean that every one in two of those lenses is bad. It just means that they were unlucky with the first, and luckier with the second. Who knows, maybe that second copy would also be deemed defective by someone with yet higher, even-more-unrealistic standards... and maybe I'd consider both copies to be perfectly acceptable. There's quite a degree of subjectivity in it, unless it's a
really obvious problem, of course.
Obvious de-centering - where you can clearly see a difference in symmetrical resolution when viewing a photo at typical dimensions and viewing distances - is a valid reason for concluding it's defective. So, too, is the inability to adjust it for accurate focusing within the camera's AF fine adjustment limits (assuming the camera isn't at fault). It's possible with any lens - even high-end models, from
any manufacturer - to have a few examples slip through quality control exhibiting these issues. We seem to feel $2,000 is a lot to spend on a complex, high-precision optical device, and we expect it to be perfect, yet we think nothing of a $50,000 - $100,000 luxury car requiring mechanical adjustment and servicing even soon after delivery. Sometimes, our ideas are out of whack to a far greater extent than our lenses