I took to try two different copies from two different people. they are as different as heaven and earth. one has constant autofocus errors even with good lighting and contrasting compositions, the trunk leaves - the sensations were terrible (half of the photos were marriage). took another copy - completely different. elastic zoom, fast and accurate focus, even in the dark, normal focus. the stub significantly stretches the photo in poor lighting . I didn’t even expect such sensations on whale lenses . (one copy has been used for more than a year, the second is almost new). therefore, either lenses have rapid wear or really unstable quality