I purchased a new Panny 12-35mm f/2.8 last week. I had decided to rationalise my growing lens collection down to a set of quality zooms to minimise lens changes. However, apart from the nice build quality, I have been sorely disappointed with its optical performance. The first problem I spotted was uneven vignetting, resulting in one dark corner (bottom right) at 12mm, even when stopped down to f/11. To me that's unacceptable on an £850 lens, so it's going back to the retailer tomorrow. As well as the uneven vignetting issue, the limited testing I have done so far suggests that the edge performance at f/5.6 is noticeably worse than my excellent Panny 14-45mm lens, at all focal lengths. Again, not what I expect from a lens costing 3x as much. I wanted a well-built lens with top optical quality, a useful FL range and fast aperture to use as a staple alongside my 7-14 and 45-200, but I ended up feeling robbed. I am expecting the retailer to offer a choice of refund or replacement (based on the vignetting issue, which I regard as a fault). My dilemma is: should I try another sample, or keep the money and stick with my 14-45? My question to you guys is: should I expect better from this lens? Have others found it better than the 14-45, or is it just an OK lens with a fast aperture and fancy build?