Olympus 12mm f/2
There are currently a couple of ultra-wideangle zooms for the Micro 4/3 format with shorter focal lengths than 12 mm. However, their high prices, quite slow apertures and not-too-exciting image quality (IQ) discouraged me. Thus, I decided to get a high-quality prime wideangle lens, and set my sight on the Olympus 12 mm f/2. My main criteria for this choice:
The focusing ring can be pulled back to display a distance scale for manual focus and use the DOF markings. Push it forward to re-engage the autofocus.
The closest focusing distance is 20 cm, which can be useful for close-up images that display an enhanced perspective rendering (unlike the "flatter" rendering of typical macro lenses of much longer focal lengths). The field of view at the closest focusing distance is approximately 22.5 x 15 cm.
Image quality is indeed excellent even at f/2, and the only reason for stopping down is to increase the DOF rather than the IQ. Together with the very effective in-body image stabilization of the E-M5, the 12 mm f/2 can be used as an effective low-light lens. The optical formula is unusually complicated, with 11 elements that include aspheric, dual aspheric, ED and one more special type of optical glass. According to Olympus, the lens also uses a new type of coating that reduces by half the reflections from optical surfaces. In my practical use, the lens has proved to be remarkably immune to flare.
This is a remarkably small lens, albeit definitely not a pancake lens. I recently used it extensively as a walk-around lens for street and urban landscape photography, and it proved quite versatile. It should not be used outdoors without an effective lens shade (as a protection against flare as well as a mechanical protection of the bulging front element), and Olympus does not include lens shades with its current lenses. Instead, Olympus makes a far too expensive, rectangular metal lens shade available as an accessory at extra cost. Fortunately, China Inc. comes to the rescue with copies or knockoffs, which, although still rather expensive, cost only one-third to one-fifth of the Olympus original lens shade, and match fairly well the silver-but-slightly-champagne-colored finish of the lens barrel. Just make a search for LH-48 on eBay, and you will find that the fakes outnumber the genuine item 5 to 1.
Some users complain that the color of the lens barrel (also used in the Olympus 75 mm f/1.8, while the Olympus 45 mm f/1.8 uses a plastic barrel with a slightly different silvery appearance, and other Olympus lenses have a more chrome-like finish) is a mismatch on both black and silver OM-D E-M5 bodies. This is not a big deal for me, since I regard my photographic equipment as a tool, rather than a fashion accessory. Some of the lenses and accessories I use on my E-M5 are esthetically much worse misfits.
Before buying the fake Olympus lens shade, I tested a few lens shades and adapters I happened to have available. The Olympus 12 mm f/2 has a 46 mm filter mount that, in principle, can accept a screw-in lens shade. However, even a rather short conical lens shade visibly vignettes in the image corners. The lens accepts a 46 mm to 52 mm step-up filter adapter, onto which an ordinary (not super-thin) filter can be mounted without vignetting. An additional step-up filter adapter (for example, 52 mm to 58 mm) can be mounted in the first adapter to make a broadly conical lens shade. However, this improvised lens shade is not optimally shaped. Perhaps a suitable petal-shaped third-party lens shade can be found, but the rectangular Olympus lens shade and its knockoffs are a better fit.
The Olympus lens shade attaches to the lens by tightening a thumbscrew, and can freely rotate around the front of the lens when loose (there is no locking notch or click-stop, only an index mark on the barrel and one on the lens shade). The knockoffs faithfully copy these features. A bayonet mount would be more practical. As it is, mounting and aligning the lens shade is a hassle, and I always leave mine mounted. The lens is small enough to fit in an ordinary lens compartment in any bag even with its lens shade mounted.
The original Olympus lens cap (equipped with buttons on its periphery only) is difficult to take off with the lens shade mounted, and I replaced it with a no-name butterfly cap. I have been reading about the Olympus brand tag easily detaching from the original lens cap, so you may wish to change to a more confortable butterfly cap even if you use a different lens shade.You can even get a lens cap with fake "Olympus" branding on eBay if you want to continue providing free advertising to Olympus.