With the announcement of a new 12-35mm f2.8 lens in its X series of Micro Four Thirds (MFT) lenses, I am now officially confused by Panasonic's lens marketing. The X series lenses do seem to have a slightly better build quality and design than the plain old Lumix G models, composed of more metal and less plastic, but all the usual markers that manufacturers use to differentiate between classes of lenses -- coatings, wide apertures, features -- are absent.
When Panasonic first announced the X series, I had though that X would be defined by the power zoom or video-optimized quieter stepping motor (designated by an HD), but there are non-X HD lenses (like the veteran 14-140 f4-5.8), and the new 12-35mm lacks power zoom. There are non-X lenses with Panasonic's Nano Surface Coating plus low-dispersion (UED) and high refraction (UHR) lenses, like its Leica-produced DG Summilux 25mm f1.4. And Panasonic doesn't have enough lenses in its lineup to use price as a discriminator.
But enough about positioning. I had a chance to use a production-quality version of the lens the weekend prior to the announcement, though I tested it on the Olympus OM-D E-M5 rather than the Lumix DMC-GF5 provided by Panasonic; in part, that's because I don't see this as a lens for the really entry-level models. For one thing, it's on the large side for the smaller cameras, while on the E-M5 it feels nicely balanced. Plus, I suspect the pricing -- once Panasonic decides to announce it -- will be on the high side for cameras in that class. (Pro tip: always remember to check your image-stabilization settings when putting a Panasonic optically stabilized lens on an Olympus sensor-shift stabilized body.)
I think 12-35mm is a perfect range on an MFT body; it's equivalent to 24-70mm on a full-frame camera, and covers everything from landscapes to portraits. With the constant aperture of f2.8, it's certainly more flexible. The lens itself certainly feels like a better build quality than the usual; the zoom and manual focus rings operate much more smoothly and more responsively than the more-plasticky lenses.
As far as I can tell, it remains consistently sharp and bright through the zoom range, with minimal distortion and no vignetting. My photos look a little softer at apertures above f11, though not egregiously so. While it doesn't focus exceptionally close, it's good enough that shifting back a couple of inches usually does the trick.
The autofocus isn't completely silent, and you can certainly hear the sound when you hit the endpoints of the zoom, but you have to be recording in dead quiet to hear it, and likely wouldn't hear it at all if you use an external microphone.
This would make a great kit lens for the GH2 -- one might speculate that when it ships in August it will be a companion for that camera's longed-for replacement -- especially if, like me, you don't like Panasonic's power zoom lenses.