Rangefinder design question

[cfrye]

I'm trying to figure out the simple little rangefinder on the folding 6x6 Ansco Speedex Special R. I understand the light path and the beamsplitter and everything, but this little lens in the optical path is throwing me for a loop. I'm talking about the 'optical element' referenced in the pic.

A closer view

Something like this appears in a lot of rangefinders. Is it the same focal length as the viewfinder's front element? Does it have to do with patch alignment or something?

 

[ic-racer]

I suspect it should have the same strength as the front element, otherwise the overlay patch will be blurry compared to the rest of the image. Are you just curious what the lens does, or is there an issue with the overlay patch image. Folders with rangefinders are great! I hope it is working well for you.

 

[cfrye]

I'm just curious. It is a really neat camera!! It's also quite old, so It's got a ways to go before it's in a usable state