Planar T50mm f/1.4
This 50mm reaches its best DxOMark low-light score at f/2.8 on both APS-C and full-frame sensors, and has to be stopped down to f/4 to achieve its best mid-light score.
This makes this 50mm a suitable candidate for portraits or reportage.
Distortion is handled well, as well as chromatic aberrations are on full-frame; these perturbations are slightly more noticeable on the edges when the lens is attached to a D300s, for instance. The biggest concern with this very fast lens is that it is hardly usable at its maximum aperture and has to be stopped down by 2 stops to reach a good enough definition.
On a full-frame sensor (D3X):
When installed on a D3x, the first noticeable detail is that opening the lens wide results in strongly deteriorated resolution, between 20 and 30lp/mm on the whole frame. The central first one-third becomes interesting when the lens is stopped down to f/2.8, and becomes very sharp at f/4and f/5.6. But the edges remain much softer. To improve them, one must stop down to f/11, thus lowering the resolution in the middle of the field.
Visible at f/1.4, vignetting disappears as soon as the lens is stopped down to f/2.8.
On an APS-C sensor (D300s):
On a smaller-sized sensor, the resolution behaves the same way: very poor when the lens is wide open, it improves considerably when stopping down to f/4 and f/5.6, but the last one-third of the field remains very soft.
At full aperture, vignetting is present, although quite light; 1 stop later, at f/2, it has completely disappeared.