I use the Canon 5D mk III, and have a roomful of Canon L lenses, from the 500mm f4.0 to the 16-35 2.8. One day I go tired of lugging a trunk-full of equipment and tried the Tamron 28-300 with optical stabilization. I found it quite satisfactory for everyday walkaround shooting, with adequate sharpness, contrast, etc for the majority of shots. Of course, for specific shoots where the highest quality is considered, I also bring whichever lenses I anticipate needing. However, the quality of the Tamron quite often is very close to what I get from the other lenses, except for speed.