I was going through some recent photos that I shot with my Nikkor 50mm f1.4 AIS lens and I'm noticing vignetting. Is this something that is common with these lenses when they are shot at wide open aperatures? Is it because it is a f1.4? Could someone explain this phenomenon?

I've never done a lens test to determine what the best aperature to shoot at is. Can someone recommend a basic test I can do to determine this?

Thanks in advance,