The Sigma 100-300 provides a unique lens not quite matched by anything else. It is fairly small and light for a zoom telephoto (similar in size to the 80-400 VR lens). With a fixed f/4.0 aperture it is faster at 300mm than the 80-400 and most other telephoto zooms. Its quite sharp and fairly easy to handhold in good light. Image quality is a bit better than the 80-400 VR, but without a vibration reduction system. Numerous reviewers state that this, along with the 120-300 f/2.8, are the best lenses Sigma makes.