The 50mm F2 macro is a member of Olympus's 'Pro' family of lenses, and is correspondingly well-built. It's robustly constructed with a metal lens mount and plastic outer barrel, with the extending section also apparently constructed of metal. Olympus advertise this lens as 'splashproof', and it incorporates seals around the mount and extending focus unit to prevent dust and water ingress. It's pretty compact for a macro lens (for example it's about 9mm shorter and 30g lighter than Canon's EF-S 60mm F2.8 Macro USM for APS-C, and about half the length and weight of their 100mm F2.8 Macro USM for full-frame), so this is one case where the Four Thirds system delivers on its promise of smaller, lighter lenses.
The most striking aspect of the lens's design is the substantial increase in length on focusing, which is far from unusual for a macro lens (although some manufacturers have now moved to ultrasonic focus-motor internal-focus designs). The main optical unit extends 34mm/1.3" on focusing from infinity to 0.2m, and the rear lens group moves separately in a floating system to maximize image quality at all distances. Unusually for what is described as a dual-purpose lens, there's no focus distance limiter switch for portrait work.
'Focus-by-wire' manual focus
The most unusual feature of this lens's operation is the focus-by-wire manual focus system, which drives the focusing group indirectly via the lens's autofocus motor (as opposed to the direct mechanical connection found in most lenses). As a consequence, the feel of the manual focus ring never changes, regardless of whether the camera is set to auto or manual focus, or the focus has reached the limits of its travel (either close or infinity), and this lack of tactile feedback can be a little disconcerting in some situations. A further annoyance is that the focusing unit can only be driven from the camera body, so if you dismount the lens in an extended position, you'll have to put it back on the camera to retract it to infinity focus. Overall, we'd much prefer to see a well-designed mechanically-coupled focus ring.
However, one advantage of this system is that it does allow an extremely long focus travel, and consequently (in principle at least) a high level of focus accuracy, which is essential for macro work. This isn't really going to help manual focus using the viewfinder of any Four Thirds DSLR bar the E-3, but it does allow very precise manual focusing in live view mode on all current Olympus and Panasonic bodies. However under the extreme scrutiny of magnified live view, the focusing action is distinctly 'stepped', and we've found this to be a slight concern on occasions when absolutely critical focus accuracy is required at wide apertures; in some circumstances the lens can step between positions which are very slightly front- and rear-focused compared to the desired result. This is most noticeable at intermediate distances (ca. 1-2m), as the focusing system appears to have been optimized for macro work.
On the camera
The lens handles well on all of Olympus's DSLR bodies, sitting snugly on the chunky E-3 at one extreme, and providing a very compact short telephoto combination with the E-420 at the other. The only external control is the manual focus ring, which falls naturally to hand when required.
Autofocus is driven by a micro motor in the lens body, which is somewhat 'buzzy' in operation and can feel a little sluggish; overall it's simply not as refined as the the ultrasonic-type motors used in some other manufacturers' macro lenses. It's also not currently compatible with the E-420 and E-520's contrast-detect 'Imager AF' modes in live view, so can only autofocus via the camera's phase detect system (which is normally much faster anyway).
Perhaps the biggest problem, though, is the lack of a focus range limiter switch; this can be an issue when shooting portraits, as the lens has a habit of racking through the entire distance range if it cannot immediately acquire focus, at great annoyance to both photographer and subject. Aside from this irritation, though, autofocus is generally fast and positive, but as always focus speed and accuracy is dependent upon a number of variables, including the camera body used, subject contrast, and light levels.
Lens body elements
Reported aperture vs focal length
The lens allows apertures from F2.0 to F22 to be selected.