Quote Originally Posted by Ole View Post
... I don't have my library with me, so I don't know what kind of lens the Ernemann "Doppel-Objektiv Serie A" is, but I know I can find out. ...
Reunited with my library, I find that the Ernemann Doppel-Objektiv is what I should have suspected from the start: A Periskop.

That's a lens consisting of two elements symmetrically placed each side of a central stop. Since these are not achromatic, a small aperture is necessary to give satisfactory performance - the f:11 should have been clue enough for me: Wide angle lenses and Periskops were generally the only lenses to come with a max opening of f:11!

BTW, I'm moving this thread to "Plate Cameras", since that's what it is.