I've owned two, the first one sucked in an unbelieveable amount of dust in a short period of time. Whether it affected IQ or not, I was not happy with paying that much for a lens and seeing all that dust. I exchanged it for another copy which in the same period of time has absolutely no internal dust. Why the difference, I don't know? I started the thread about the possibility of a UV filter preventing dust because that is my only difference between lens one and two. I thought it was worth asking just in case that was the source of dust entry but no evidence to indicate that yet. In two weeks of ownership of my first lens, I could count about 2 dozen specks of dust internally, had it continued I can't help but think that it could affect IQ in certain situations with strong backlighting.