Quote Originally Posted by Terry Christian View Post
As for your second question, you can tell a real rangefinder (as opposed to viewfinder cameras) from the patch in the middle of the viewfinder image. Aligning this patch with the rest of your view focuses the image. Simple viewfinder cameras will have framelines to help you compose, and they may even adjust for parallax, but no patch.
This is correct, with one caveat.

There are range-finder cameras that present you with two windows to look through.

The larger, brighter one you use for framing your subject.

The smaller, "squintier" one is used just for focussing - it has a coupled range-finder patch that you align for focussing. The view through that window may only be part of the scene.

I don't know if there are Leica versions of this approach, but there certainly are others. The rangefinder versions of the Kodak 35 are an example.