50 State Quarters to form what is known as a "mule". Only sixteen of these specimens, produced on dollar planchets, escaped from the mint. A 2005 Minnesota double die quarter, as well as a 2005 Minnesota quarter with extra trees (another die error), have both triggered numismatic interest. An unusual die break on some 2005 Kansas quarters created a humpback bison. Relatively more common are Kansas quarters bearing the motto "IN GOD WE RUST." The United States produces proof coinage in circulating base metal and, since 1992, in separately sold sets with the dimes, quarters, and half-dollars in silver. For the silver issues,
Micro Four Thirds system PDAF focusing systems. Olympus then introduced the first live view DSLR camera, which incorporated both traditional DSLR phase focus and also optional contrast detection focus. As a result, newer Four Thirds system lenses were designed both for PDAF and contrast focus. Several of the Four Thirds lenses focus on Micro Four Thirds proficiently when an electrically compatible adapter is used on the Micro Four Thirds cameras, and they focus on Micro Four Thirds cameras much quicker than earlier generation Four Thirds lenses can. Some MFT cameras, such as the OM-D E-M1 and E-M1 Mark II incorporate phase-detection hardware on the