From the Phoblographer:
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Finally, half a year after the development of this lens was first disclosed by Panasonic, the Leica DG Summilux 15mm f1.7 ASPH. has now been officially announced. The lens is the first Micro Four Thirds lens to feature a physical aperture ring and looks almost like it belongs on a proper Leica rangefinder camera. Unlike a proper Leica rangefinder lens, though, the designation ‘Summilux’ is a bit misleading as its initial aperture is really only f1.7, and not f1.4.
The lens sports an internal focusing mechanism that promises super fast autofocus when combined with Panasonic’s latest Lumix G camera models that support 240fps sensor readout. It sports 9 lenses in 7 groups, three of which have aspherical surfaces. To further boost image quality, the 15mm f1.7 Summilux has been treated with Panasonic’s Nano Surface Coating.