The 35-100mm uses essentially the same premium construction as the 12-35mm F2.8. The rear segment of the barrel between the zoom ring and the mount is made of metal, as is the manual focus ring with its finely-milled ridged grip. The slim rubber seal that encircles the mount is the sole external clue to the lens's dust- and splash-proof design. Zoom and focus are both entirely internal, so the lens always stays the same length at every setting.
Both the zoom and manual focus rings are smooth in operation, but while the zoom is mechanically coupled, the focus ring is electronic. However such 'focus-by-wire' systems have improved immeasurably over recent years, and Micro Four Thirds bodies from both Panasonic and Olympus offer a manual focus 'feel' that's a pretty good facsimile of a traditional mechanically-coupled lens.
On the camera
The 35-100mm isn't a large lens by any means, but it still contrives to look bulky on most Micro Four Thirds bodies. It's certainly best-balanced on SLR-like bodies such as the DMC-G5, DMC-GH3 or Olympus OM-D E-M5, and like all lenses benefits from the extra stability of being shot using an eye-level viewfinder. It still handles reasonably acceptably on the 'rangefinder-style' DMC-GX1 or the Olympus PEN E-P3, but with these small bodies it's likely to benefit from the use of an add-on EVF.
The 35-100mm F2.8 is so small that it's barely bigger than its 12-35mm F2.8 little brother. Indeed when the latter is zoomed to 35mm, only a couple of millimetres separates them in length. Compared to a full-frame 70-200mm F2.8 it's absolutely tiny, and a fraction of the weight; but the trade-off is that the smaller lens can't provide anywhere near the same degree of subject isolation and background blur.
Lens body elements
The 35-100mm uses the all-electronic Micro Four Thirds mount, meaning it will work on Olympus's PEN and OM-D cameras, as well as on Panasonic Lumix G bodies.
In this view you can see the slim rubber seal that surrounds the mount, and helps protect against dust and water getting into the body at this relatively vulnerable point.
The filter thread is 58mm, and does not rotate on autofocusing, which should please filter users.
Next to it is the bayonet mount for the petal-type lens hood (see below).
The zoom ring is a generous 37mm wide, and rotates approximately 60 degrees clockwise from 35mm to 100mm.
Olympus users may wish to bear in mind, though, that (as usual) this is the opposite direction of rotation compared to their M.Zuiko Digital zooms.
The finely-ridged manual focus ring is 10mm wide, and unusually is made of metal. Like most Micro Four Thirds lenses manual focusing is 'by wire', and geared such that rapid rotation of the ring changes focus distance quickly, while slow rotation can be used for fine focusing.
Panasonic's implementation works especially well, but it does mean that there's no distance scale on the lens.
Thankfully the 35-100mm has a physical OIS switch; many recent Panasonic lenses have devolved this function to a menu setting on the camera.
For users of Olympus cameras, this allows relatively easy switching between optical and in-body IS systems. On the OM-D E-M5 we'd recommend using the in-body system, due to its ability to correct for rotation around the lens axis.
The 35-100mm comes with a deep, cylindrical bayonet-mount hood, that reverses for storage. You can just about operate the zoom ring when the hood is reversed, but the focus ring is entirely blocked.