After some disappointment with a (favorable) Tamron 300mm telephoto for Canon I was skeptical about light intensity, sharpness and distortion. So far I am from the results but thrilled: Even with soft lighting succeed hochzuschrauben (on the Lumix GH3) great pictures, even without lens and without photosensitivity, until the image is grainier than a granola bar with this lens. Involuntarily I have also tested the stability and water sensitivity of the lens and am equally relieved and thrilled! :-)
While I actually left my old 300er Lens always at home because it was too heavy and did too little, I take the considerable weight of this Teles very happy for me.