What really is a "bad copy"?

Started 3 months ago | Questions thread
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Roadiez
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What really is a "bad copy"?
3 months ago

I've just received my Tokina 16-28 f/2.8 from B&H. I've read a lot about it before purchasing it. I read that this lens is reasonably sharp wide open, and greatly improves stopping down.

I tested it on various lighting condition, and found that at f/2.8 it's so soft and blurry its really unusable under almost all conditions. However, as soon as I stop it down to f/4, it is very sharp.

I've compared my image to the sample image on the internet, and found that my lens is more blurry (both at f/2.8). But at f/4, it's excellent, no problem at all.

I'm perplexed because I don't know if it's a bad copy. What constitute a "bad copy"? If it's sharp at some stopped-down apertures, is it by definition not a bad copy? If it is "bad", is it bad at all aperture? Or is it possible for some defects to affect the widest aperture?

I'm just debating whether I should go through the hassle to do an exchange.

Thanks.

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