Review on Samyang SY12M-MFT-SIL 12mm F2.0 Ultra Wide Angle Lens for Olympus/Panasonic Micro 4/3 Cameras, Silver: A Perfect Lens for Stunning Landscape and Architectural Photography by Jason Dahlkemper

Well built, bright lens with detachable/reversible lens hood and delicate cloth case. Excellent image quality in the center even at full aperture. Significantly cheaper than the Olympus 12mm f2, for example. Recommended for astrophotography. Like other Samyang/Rokinon lenses, it doesn't have electronics: manual iris, manual focus (but the ultra-wide angle has a large depth of field, so it's not that important). 67mm filters are used. Unfortunately there are no focus markings and no depth of field markings between 3ft/1m and infinity.