Sigma 400mm f/5.6

I bought this lens for very little money though the local classifieds, and I'm happy that it wasn't too expensive, because it's a really lousy lens! 400mm and f/5.6 for little money might sound like a sweet deal, but it's a small and optically subpar lens with a pretty coarse mechanical construction. It has trouble conveying the right aperture information to the camera (says it f/7.2 all the time), and doesn't really excell in any field - brightness, AF or sharpness.