The 1930 Photo Post Catalog illustrates a tiny masking device fitting over the 5cm viewfinder of the Leica C. The opening at the front of the mask is configured to cover the field of view of the 13.5cm 1:4.5 Elmar. Until recently the only sample I had inspected is shown on page 14 of my Volume III-Accessories. An additional specimen is shown here.
The cap type mask lacks Leitz identification. It appear very few were prepared as the more commonly encountered swingin style mask was under the development concurrently. In over four decades of research I have inspected only two samples. Have more survived?