Instruct: Classify a given Amazon review into positive or negative sentiment.
Query: So much potential; so little QC

I tried four copies; three were bad, one was awful. This lens has been very favorably reviewed, and I find their 50 f1.4 to be magnificent, so I took a chance. The only thing I can think, based on what I saw in the files, is that in each case, one or more of the elements was out of alignment, because they didn't produce a normally focused image at any focus distance. Something 10 feet away on one side would be in focus, and something fifty feet away on the other side would be. Very strange.