When I say no two lenses are the same, I do not mean that various models have differences between them (though they do, of course). Rather, I mean that every individual lens — even those of the same model — differs from the next, and it is well worth understanding the implications of that to make sure your lenses are of the highest quality possible.
Coming to you from Michael The Maven, this great video talks about a rarely discussed issue involving lenses: how individual lenses within the same product line can vary in quality. The issue comes down to manufacturing tolerances. Simply put, no manufacturing process is perfectly precise, and as such, individual copies of lenses may vary slightly in their quality. Manufacturers put limits on how much variation is allowed in any one copy, however. This is why you will sometimes hear photographers talk about having a "sharp copy" of a lens. Nonetheless, whenever you purchase a new lens, it is important to not just assume that your copy is perfect; be sure to take time to carefully examine shots you take with it to make sure it is performing to the standards you expect of it before the return window closes. Check out the video above to learn more.