Leica M - NEX adapter issue

Hi,

I have been using one of the generic Leica M to NEX adapters. It works fine as far as fitting both mounts, but I noticed that when I focus my actual focus does not correlate too closely to the distance scale. It is somewhat of a problem if I use the DOF marking and it seem to increase minimal focus distance.

Does anyone else have a similar problem? Is this a matter of imprecisely designed/manufactured adapter? Or is this something that is unavoidable when coupling Leica lenses with E mount?

Do you think Voigtlander adapter would work better?
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Eugene
http://fratkinphoto.com