Mine (a black version still being named W-Nikkor-
C) doesn't really get sharp in the extreme corners before f/8. At f/11 it's excellent enough all over the frame. But at f/5.6 it is very good enough too if you prefer looking at the photo than peeping at the corners sharpness.
In a nutshell : not a stellar lens as for sharpness in the corners for sure, but it is so cute and so tiny and so lightweight that you can use it handheld until 1/4s with no problem. And it has so little distorsion if any, and such a good resistance to flare for an old lens. Also, remember : sharpness is a bourgeois concept.
😉
Chicago Union Station, October 2018 :
Ernest Hemingway's birth house, Oak Park, IL, October 2018 :
Nikon S3 - W-Nikkor-
C 2.8cm f/3.5 - Fuji Neopan 400 - D76 1+1.