This lens has had some very mixed reviews, it's a toss up between this and the similar range Sigma as to which is best. Some reviews favour one, some the other.
I decided on this because I've had Tamron lenses before (many years ago) and always found them to be high quality.
I'm very glad I did buy this one!
The lens is not perfect, but for the price it's damn close.
Wide open it's fairly soft at most magnifications, but close it down a stop or two, and the story is very different. Everything seems to sharpen up a huge amount, it then becomes a very capable lens. The colour saturation is spot on, natural and accurate.
Barrel distortion at the wide end is more than acceptable; pincushion at longer settings is also well controlled. Contrast is strong and edge definition is surprisingly good for a lens of this type. Chromatic aberrations are evident, but only in high contrast detail where most lenses exhibit these. They are no worse than on the 18-55 Canon lens I also use.
The construction may be mainly plastic but it handles and feels like a quality, well made product. The zoom ring operates smoothly and evenly, as does the manual focus ring. The overall build feels solid, well designed and durable.
Having one lens that covers such a large range of focal lengths is remarkably convenient. for trips, holidays etc it's the ideal "walk round lens" Not having to fumble around changing lenses means your less likely to miss that shot when the moment presents itself.
All lenses of this type are a compromise between convenience and quality, but I would rather catch the shot and sacrifice some quality in absolute terms, than miss the shot altogether!
For the cost, just over £150, this thing is a steal.