This is probably one of the Best U.W.A Micro 4/3 lens and probably the one I use the most ! (Along with the Olympus 12-40 F2.8)
PANASONIC 8-18 MM F2.8/4:
PROS

First things first, the build quality is exemplary !
Maybe because of the specifications of the famous brand LEICA which stamped the lens with its name.
Entirely made of metal, the Panasonic Leica 8 18 is weather sealed, protected from water drops, dust and even frost, inspiring great confidence.
The focus and shift rings are very smooth. Some will complain that the focus ring is infinite. However, I confess I have never been bothered by this detail.
Panasonic has managed to produce a lens of superb optical quality, weighting just over 300 grams.
However, to do so, they had to make the compromise of a sliding and not constant aperture, which is more annoying in video than in photography.

Above all the sharpness, it is superb at full aperture in the center and a little recessed on the extreme edges. It improves by closing to f4 or F5.6.
It has an undeniable advantage over its two competitors, the 7-14 f2.8 Olympus or the 7-14 Panasonic: It is possible to screw in 67mm filters.

CONS
Expensive!
Like many ultra wide angle lenses, vignetting is present at full aperture at 8mm. It is easily corrected on post production software.
No constant aperture
CONCLUSION: It is a high-end U.W.A Micro 4/3 lens with an exemplary quality of manufacture and optics.
Wish to Buy the PANASONIC 8-18mm ? ( Amazon Affiliate Link that would help me to continue the adventure…It won’t cost you anything more and i’ll receive a little contribution)