<p>Martin Tai wrote,</p>
<blockquote>
<p>For example, Contax 55mm UV filter for Carl Zeiss Planar 50/1.4 has the right thread, it can fit onto a Summicron 50/2, however Contax 55mm filter has a outer diameter = 59mm, it jams up the built in lens hood of Leica lens, making it inoperable<br>
Only E55 filter permits the built in lens hood on Leica R lenses operable.</p>
</blockquote>
<p>I bought b+w 55mm filter UV MRC recently, it fits my Leitz Canada Summicron R 50mm f/2 with builtin hood. Hood operates without jam problem. </p>