Ernemann Anastigmat Ernostar 2,7/ 15cm

 Ernostar was designed by Ludwig Bertele in 1923-24, who later also designed Sonnar in approx. 1930 and Biogon in 1935

this is the design of original Ernostar from wikipedia

Possibly from Zeiss Ikon's Klapp miniature or Ermanox camera.

from http://www.collection-appareils.fr/x/html/page_standard_eng.php?id_appareil=20214

I use Lens turbo+NEX at maybe F4 or 5,6. looks nice with lens turbo, sharpness at edges

 All other shots are wide open