Opticallimits (former Photozone) tested the Panasonic-Leica 8-18mm lens:
As you might expect, the Leica DG Vario-Elmarit 8-18mm f/2.8-4 ASPH is a very decent performer in its category. The image center is very sharp and the borders and corners are pretty good as well – technically at least. Field curvature is a bit of an issue at 12mm albeit that’s not unheard of in this class (albeit usually at the wide end). Image distortions as well as vignetting are low when taking advantage of image auto-correction (obviously). The quality of the native design isn’t quite as hot in these respects though. Lateral CAs are very low and contribute to the high-quality perception. If pushed you will be able to spot some ghostings are a bit of glare with strong light sources in the scene. However, it isn’t worse than the competition in this respect.
A highlight of the lens (as well as its Leica cousins) is the build quality. We really wished this would be standard across all lenses. The Leica lens feels both sturdy and extremely well assembled with smooth controls and weather sealing on top of all that. Some may regret that Panasonic skipped an image stabilizer but honestly we agree with this approach because it’s already difficult enough to produce ultra-wide lenses without much sample variations.
Overall the Leica DG Vario-Elmarit 8-18mm f/2.8-4 ASPH follows a balanced approach in this category. It skips a constant aperture in favour of having front filters combined with a compact size. We wouldn’t state that it excels compared to its Olympus and Panasonic mates but it is in the very same league and as such an appealing option.