When talking about the technical IQ a lens is capable of in a lab bench test then most are good enough in everyday handheld use. In everyday use I see little difference between my Nikon and Leica glass. At lest not enough for me to get excited about but ymmv. If you are talking about the IQ of the final image then there are far more things to consider and explains why I can produce equally crappy images with expensive or cheap glass. The two should not be confused.
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