There's no such thing as a free lunch and the Tamron is no exception here. The extreme zoom range combined with the small lens dimensions comes at cost of some compromises. One is the rather slow max. aperture which limits the creative potential regarding shallow depth-of-field and the other compromise is, naturally, optical quality. In absolute terms the lens shows rather extreme distortions at the 18mm and vignetting as well as border quality don't impress either. The latter is also true for the 200mm setting. Nonetheless the lens is capable to deliver decent quality images under controlled conditions - reads: f/8 (see also the sample shots). In the field the Tamron AF 18-200mm XR felt far more convincing than the Sigma AF 18-200mm DC thanks to a decent AF performance so if it has to be such an extreme zoom lens the Tamron is the better bet. For critical applications you should consider to split the zoom range into at least two lenses though.