[boren]

Well, of course, I can't the accuracy of your test here but I'd say that these differences between right and left are beyond acceptable margins.

I'm not a native English speaker, so want to make sure - when you say "beyond acceptable margins" you mean within acceptable margins or unacceptable?

[JJ_SO]

I'd recommend DeepL.com for a better translation than Google's. The meaning is "unacceptable" in this context. But Klaus' first sentence also lacks of what he can't I guess he wanted to say "I can't comment..." or "...can't judge...".

[Klaus]

@Boren - yes, this means unacceptable.

@JJ - I thought that I trained you that much over the years that my skipping of words has no impact anymore ;-)

[JJ_SO]

You, Klaus: It's a. Always fun to.

[boren]

Thanks for the clarifications. I think I'll keep my 16-50/2.8 because actual pictures look very good, even wide open. I will however keep this in mind when buying lenses in the future and will use this method, as it's really simple to execute. The limits I'll consider as "acceptable" still need to be defined :-)

On a related question - are de-centering issues more likely to affect the wide or the long end of a zoom? In other words, if I have limited time to test a lens, which end should I prioritize?

[Klaus]

Thanks for the clarifications. I think I'll keep my 16-50/2.8 because actual pictures look very good, even wide open. I will however keep this in mind when buying lenses in the future and will use this method, as it's really simple to execute. The limits I'll consider as "acceptable" still need to be defined :-)

On a related question - are de-centering issues more likely to affect the wide or the long end of a zoom? In other words, if I have limited time to test a lens, which end should I prioritize?

There are no rules here - I've seen both ends with issues.

At the wide-end you tend to have more issues with asymmetrical sides whereas the center remains very good.  
At the long end, you "magnify" any issue while essentially cropping the corners. Thus the corners are often symmetrical but there's an overall softness.

But, as mentioned, there's a wild mix of everything out there.

[you2]

I always wonder how we determine what is and is not acceptable....

[Hapo]

...wow...the first thing I see after registration is that the sole "important topic" addresses the very issue I was concerned about...

...how does one tell if they lens they just bought is centered...???...indeed, what is centered...???...

...not sure if reading this thread will help...a lot seems over my head...