Schneider Karat-Xenar 5cm F2.8 from last week's Photorama show, loose lens/ no body. $30, Hacked into Leica Mount using the focus mount from a Canon 50/2.8 (unuseable glass on the canon, etching). The Karat-Xenar is a 5-element in 4 group lens. Looks like it is based on the Tessar, but uses an air-spaced doublet for the front section. It is much sharper than my Zeiss 5cm F2.8 Tessar of the same period, 1930s.
Turns out the threads on the lens are the same as the retaining rings on the I-61, and the retaining ring of the Canon is close. I used a little teflon tape made for pipe fittings to secure. The trim ring on the filed-down Canon barrel is from a parts Kodak TLR. The split ring from the I-61 is used as a variable-stand-off to calibrate the lens for correct focus.
Lots of filing and testing using a TTL viewer.
Was it worth the trouble???