Quote:This applies more to young mirrorless players than DSLR users. Canon and Nikon have... decades of experience building AF and IS lenses and have tight tolerances - according to roger @ LR only 2-3% of lenses from each of them are sent back as duds.
As far as copy-to-copy variance when out of spec lenses are removed, canon varies ~7% and sigma varies over twice as much at ~13%. They absolutely are not beating canikon at tolerance levels, and Zeiss is even better than those two.
Maybe it applies more to mirrorless I cannot say, what I can say however it "definitely" applies to DSLR users with regard to Pentax, Sigma, Tamron and some others. From Canon and Nikon I cannot say. My personal experiences from Sigma, Pentax and Tamron are poor,these are in the Pentax mount.
Below par modern lenses purchased:
Sigma EX 10-20mm 4/5.6 decentered returned repaired, a decent copy.10 week wait.
Sigma 50-150mm EX II F2.8, badly decentered, shop exchanged for a good copy
Sigma 18-50mm EX F2.8 badly decentered sold on at a loss.general disgust.
Sigma 50-500mm EX F4/6.3 bought S/H decentered at 50mm , living with it as I use the longer end.
Tamron 17-50mm decentered returned repaired, a good copy. 11 week wait
Pentax, DA 21mm F3.2 Limited, decentered, returned was sent another good copy.
Pentax DA* 16-50mm decentered returned for a refund.
Good modern lenses purchased.
Pentax FA 50mm F1.4
Sigma 105mm EX F2.8 Macro
Samyang 8mm Fisheye F3.5
. I've never had a decentered all metal lens going back to the seventies, I still have a few all are perfect.
Statistics will never be complete and we will only know of a small percentage of lenses sold, that's the reality, in the end I'm only interested in "the lens I have in my hand" not the statistical ones! I now have all the lenses I need, and am taking a permanent sabbatical from lens buying.
Let's hope that Sigma's promise of tighter quality control is a reality, so far I've seen very little of decentering in recent reviews of the art and their other series.
BTW. I hold Roger Cigala of Lens Rentals in very high esteem, he's doing a great job!
There is a substantial difference between now and then ( the 70s ).
AF lenses have a comparatively small focus group - because AF motors work faster with a lower weight unit - and, and that's worse - the focus group has a low friction implementation. Or in other words - the focus group is rather 'loosely' mounted - because AF motors don't like friction either. An inferior centering compared to manual focus lenses is therefore inevitable. Add optical image stabilization on top ...
Quote:
Statistics will never be complete and we will only know of a small percentage of lenses sold, that's the reality
The dud stats are derived from a couple thousand lenses from each manufacture (Roger @ LR), the sample is plenty large for calculations with alpha=0.05 and a tolerance of +/- 10%.
Quote:
AF lenses have a comparatively small focus group - because AF motors work faster with a lower weight unit - and, and that's worse - the focus group has a low friction implementation. Or in other words - the focus group is rather 'loosely' mounted - because AF motors don't like friction either. An inferior centering compared to manual focus lenses is therefore inevitable. Add optical image stabilization on top ...
More than just that. Take the modern lens with 16 elements or the vintage lens with 7 elements and wonder which is more complex to manufacture. Factor in that the modern lens achieves radically higher levels of correction, and the effects of it not being assembled correctly become more readily apparent. Lots of old lenses are 50mm f/x.x lenses, which are all planars. Planar is very simple, and doesn't even have a "focusing group" (move the whole assembly) so it should come as no surprise that it is easy to center...
Obviously I had a run of bad luck, as I would have welcomed a 13% below par rate with open arms!
I also had some troubles with the Tamron 17-50 on Pentax and the lens travelled more than me by sending it from Switzerland to Tamron Germany. Twice, once with the body. At that time I wasn't used to the shipping costs 
Thanks for reminding me, dave's clichés how much easier my life is since i abandoned the Pentax boat. On the other side, at the time I had some Pentax and Sigma lenses I had not idea what happens if a lens is decenterred. And am pretty sure, I wouldn't have been able to recognize one. Anyway, I was pretty happy with my 4 Sigmas at that time.
Talking of moving elements of lenses: I always remained sceptical to Pentax' inbuilt vibration reduction - a moving sensor brings another variable into the game. What, if the motors or electronics is a bit faulty? Trying to compensate shutter vibration can fail.
Quote:I also had some troubles with the Tamron 17-50 on Pentax and the lens travelled more than me by sending it from Switzerland to Tamron Germany. Twice, once with the body. At that time I wasn't used to the shipping costs
Thanks for reminding me, dave's clichés how much easier my life is since i abandoned the Pentax boat. On the other side, at the time I had some Pentax and Sigma lenses I had not idea what happens if a lens is decenterred. And am pretty sure, I wouldn't have been able to recognize one. Anyway, I was pretty happy with my 4 Sigmas at that time.
Talking of moving elements of lenses: I always remained sceptical to Pentax' inbuilt vibration reduction - a moving sensor brings another variable into the game. What, if the motors or electronics is a bit faulty? Trying to compensate shutter vibration can fail.
I've been happy with the SR system from the Pentax K5, with one caveat, you must wait until the green hand is alight, other than that it's good and "very reliable" and there's no glass elements moving around. The AF is it's Achilles heel, but even that is decent enough once you get the hang of it.
Now I have martyred my way through those decentered lenses and have a good range of glass from 8mm fisheye through to the 50-500 Sigma , I will live with it for years, not going through that again in another mount.
It will be a K3 soon for the extra resolution and better AF, one thing you can say about Pentax is it's handling, ruggedness and compact size, if I can't get decent photos out of that lot it's me that's no good not the gear!.
If I was starting over again I would have gone Nikon.
Today I'm happy I made the switch to Nikon. Altogether there are some advantages being mainstream, such as a lot of DAM apps, big lens choice (for Pentax, the 18-35/1.8 Sigma is available nearly one year after introduction for Canon).
And now I'm looking forward to D810 
Quote:Today I'm happy I made the switch to Nikon. Altogether there are some advantages being mainstream, such as a lot of DAM apps, big lens choice (for Pentax, the 18-35/1.8 Sigma is available nearly one year after introduction for Canon).
And now I'm looking forward to D810
It would be difficult to criticize that choice of camera, it looks another Nikon killer!
At least the kevlar shutter doesn't work better with a lot of oil :lol: So there's a chance they leave it away. I hope, the shutter will be more quite than the wammbamm of the D800
They claim it will be quiet, or a least quieter, didn't realize it was kevlar!
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