I've tried both Nikkor 20mm f/4 and f/2.8 AI on film cameras and they are pretty sharp with the f/4 rendering a better image overall in terms of edge sharpness, the f/2.8 is soft around the edges below f/8 on my sample. Even though these are manual lenses, I would recommend them for landscape and even street photography, just make sure you don't tilt them too much along the vertical axis when shooting people.
As for vignetting with PL filters, I managed to solve this problem by getting a larger diameter filter and a step-up ring. Note that the f/4 has 52mm diameter and f/2.8 has 62mm, so I use a 72mm filter with 52-->72 and 62 --> 72 rings respectively.
regards
Andrew
