The Olympus M.Zuiko Digital ED 100-400mm F5-6.3 IS Super-Telephoto Zoom Lens is a high-quality lens designed for Four Thirds mount cameras, specifically those in the Olympus M. Zuiko series. With a maximum aperture of f/5-6.3, this lens offers a versatile focal length range of 100-400mm, making it perfect for capturing distant subjects with ease. It features both auto and manual focus options, a sturdy build with a length of 205.7mm and a weight of 1120g, and is equipped with a 72mm filter size for added convenience. This is a handy lens for birding as it is quite portable for its focal length.