Leica 50-200mm lens at BHphoto, Adorama, Amazon, Panasonic.
Gordon Laing from Cameralabs published the full 50-200mm lens review:
The Leica DG 50-200mm f2.8-4 is a compact and high quality telephoto zoom for Micro Four Thirds bodies upon which it delivers a 4x range equivalent to 100-400mm. This is an ideal range for sports, action, distant portraiture and some wildlife too. The focal ratio may not be constant, but is sufficiently bright to give it the edge in low light and shallow depth-of-field performance over cheaper telephoto zooms. The focusing is fast and quiet, the optical stabilisation achieved up to six stops in my tests, and like all of Panasonic and Leica’s collaborations, the build quality is excellent with smooth mechanics and a weather-sealed body. The compact dimensions and light weight also mean you’ll almost always have it with you in your bag, versus larger models which often get left at home. The smaller size, longer reach and presence of optical stabilisation are the key benefits over the Olympus 40-150mm f2.8 PRO, but it’s more expensive and lacks the constant aperture, crispness at shorter focal lengths, and physical benefits of its rival, so think carefully about your needs. Ultimately though another worthy addition to the Micro Four Thirds catalogue and one I can recommend.