What types of rangefinders are there and what are the differences between them?

Question

I have watched videos on YouTube showing the view through the M9 viewfinder, and it appears that only a small window in the middle allows you to focus. However, I once tried out an old Voigtländer rangefinder, and it looked as if the entire viewfinder consisted of two images, laid above each other.

I tried to search the internet for more information about these differences and attempted to find out what cameras have which type of rangefinder. However, I couldn't find anything, probably because I don't know the technical expressions.

Therefore, I ask you: What types of rangefinders exist and what differentiates them? I would also be very thankful if you could explain to me which type of rangefinder, in practice, is more useful for what purpose.

Answer 1

The Leica M9 - like most(if not all other) rangefinders focuses using a superimposed image in the center of the frame. Focus is achieved by lining up the superimposed image till it and the background become one. This will give you focus on the part of the frame covered by the metering field.

I believe the two cameras you considered as having different focusing methods in fact have the same. You may be confusing the M9's "bright-line frame view" feature with the focusing method as described above.