to do a side by side comparison test is a scientific job.
I tried my best
D800 on tripod
use flash light
1/200s
around 1m focus distance
I use manual tuning focus adjustment on D800 liveview, but still for the full open aperture, any 0.5degree angle difference could conduct different results.
so this is just for you referance
50/2 Ai vs Nikkor 50/1.8 Ai-S pancake 饼干版(全金属日版) @f2
100% of the resolution