I'm on my second Xpan II after foolishly selling my first one. I recently shot some B&W landscapes here in New Mexico (bright blue sky, intense sun) using the 45mm lens w/ center filter and a medium yellow filter on top of that. All was well except the central sky portion was considerably darker than the rest of the sky. I've no idea why this happened but perhaps the medium yellow was too strong. I'm going to try a light yellow filter next time. Any suggestions?