I had the chance to test this superb goal on my GM1 while traveling picture in Japan. This goal is a wonder, the sharpness is much higher than other goals I've seen on my test GM1. The visor is fixed, although it protects the lens but discomfort for when using the built-in flash. The cap comes to cover the sun visor for excellent protection.
No barrel distortion is remarkable for such a focus. That would be the ideal goal if we could find in Europe at the same price as in Japan.