Both the Olympus and Panasonic lenses have bulbous front elements that are protected (a little) by tulip-petal lens shades. The shades stick out far enough that one could put the lenses face down on a flat surface without having the glass scratched. The shades are cut out at the corners so that they don't cut off the image. Both lenses are set up so that the front glass sinks into the shade as the lens zooms to higher focal lengths, so the shades remain effective.
 

The Olympus lens is much larger than the Panasonic. As we tested the lenses, the difference seemed greater, because the Olympus had an adapter on it to make it fit the Micro Four Thirds test camera. Still, adapter or no, the Olympus is a much bigger item. A little perspective: Canon and Nikon have 10-22mm and 10-24mm zooms, respectively, for their APS-format DSLRs. These lenses offer nearly as wide a view as the Olympus and Panasonic optics. The Nikon weighs slightly more than 16 ounces and the Canon a bit over 13 ounces – so the Olympus weighs twice as much as the Canon. Both the Canon and the Nikon Ultrawide zooms are smaller than the Olympus and larger than the Panasonic.

The Olympus lens is bigger than the Panasonic probably because of design constraints imposed by the Four Thirds format. The distance between the lens mount and the focal plane is much greater on Four Thirds than on Micro Four Thirds.

Neither the Olympus nor the Panasonic can accept filters. Practically, any flat filter you could put in front of the lenses would vignette, and would degrade image quality toward the edges. It's really not much of a loss photographically: color correction is better done with custom white balance or post-processing. Putting a polarizer on such a wide angle lens would be problematic because the effect of the polarizer would vary so much across a 114-degree field. The significant drawback of not being able to put filters on the lenses is that the front element is bare and vulnerable when the lens is in use.

Both lenses have separate zoom and focus rings, with focus in front. The Olympus has a distance scale, which the Panasonic lacks. The fit and finish and quality of materials are good on both lenses. They seem durable.