In terms of outright performance, the EF300mm f/2.8L IS USM lens from Canon is right at the top of the tree. Along with the Mark II version, it ranks as the best performing long focal length lens ever tested by DxOMark. When mated to an EOS 5D Mark II, it ranks as one of the top five sharpest lenses, only beaten by its Mark II version and much shorter focal length lenses.
In terms of resolution across the frame, the lens is very homogenous. In other words there is no real drop off from the centre to the edges of the frame. No matter what aperture you choose to shoot at, be it wide-open at f/2.8 or stopped down to f/11 the lens performs almost identically. It’s only when the aperture is really closed down, beyond f/11, that the quality can start to drop of. Even so, by f/32, although the quality has fallen, the sharpness is still even right across the frame.
Lens vignetting, while not perfect, is also well controlled. At the maximum aperture there is a slight tendency to vignette at the edges, showing a drop of 0.3EV 40% out from the centre and -1EV at the very edges. At f/4, the vignetting is reduced further still, showing a drop of -0.3EV 84% of the way from the centre and -0.5EV at the very edges. From f/5.6 onwards, there is no measurable vignetting anywhere across the frame.
The other major areas of lens performance also produce very good results. At every aperture, Chromatic aberration is very well controlled leading to almost completely homogenous field maps right across the frame – put simply, there is none that is appreciably measurable or that would be strongly visible in a final image.
Equally, the distortion is also very well controlled. Long lenses are usually susceptible to pin cushion distortion where straight lines will appear to curve inwards slightly. However, there is no such distortion here, even out to the very edges of the frame.