Sorry if this isn't the best dept for this question, I'll start here, since it perhaps has a "general" element to it.
These days, all sorts of analog to digi-cam adapters are available, to enable one to shoot their vintage analog lens on many digi-cams.
Fine so far.
I ran across this widget on "that auction site", and wondering if it really has any practical use:
It is an adapter to fit Voigtlander Bessamatic and Kodak Retina lenses to Canon EOS cameras.
Since the rear element of the Bessamatic and Retina stays with the camera, it would seem that there might be difficulty getting those interchangeable lenses to focus on the digi cam ?
What would the result be ?