A couple of years ago I switched from a full-frame Canon camera to micro four thirds largely because I had become tired of humping around heavy kit. Lenses like the Canon 500mm f/4 are frankly hard work and increasingly difficult to travel with. In general I am pleased I made the change and for my long focal length wildlife photography the Olympus m43 cameras with the 300mm f/4 (600mm full-frame equivalent) still make alot of sense.