Taking Apart an old 400mm Camera Lens

What's inside a camera lens? Well, not much, in the case of this old but sturdy 400mm Pentor lens... 
This lack of frills and special features makes it even more interesting to stare in guts, as every screw on this piece of gear has an immediately evident function to it, there is nothing misterious about it. Yet this metal tube, with a couple of glass bits at its ends is, in all it's simplicity, is a functioning photographic lens, and can deliver quite decent images, provided you know and accept its limits.

Let's see what's going on inside it!