SLRGear has just reviewed the 18-135, their sample wasn't much better anyways. So it's likely the way that lens is.
Say... am I the only one who thinks that their 18-135 is basically the same as the Tokina 16.5-135mm, which had showed similarly poor image quality in PZ testing?
Say... am I the only one who thinks that their 18-135 is basically the same as the Tokina 16.5-135mm, which had showed similarly poor image quality in PZ testing?