Whilst reading about Nikkor 135mm f/2 and 135mm f/2 (Ai-S variant), I stumbled into Pierre Toscani's website. He has some really good explanations with excellent illustatrations on various things - especially the Appendix section of his site. Somewhat technical, but Imho, it's worth sharing.
Bests,
Ashfaque
Bests,
Ashfaque