New answers tagged build-quality
2
If the glass elements move at all (except for the zoom and focus movements obviously) it will impact image quality, the exact problem depends on the glass movement but common problems are softness (often unevenly across the frame) and focusing problems.
If the plastic parts of the barrel become wobbly without moving the glass it shouldn't effect image ...
2
Depending on the build quality of the lens, the optics themselves are probably on very rigid guides. It's not necessarily all that uncommon for a focus ring to get a little loose as gears wear down. I'm not sure what you mean by the inner barrel coming loose, but if the lens can slide without turning the zoom ring, that's also a fairly common problem. ...
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