122 film is postcard format; 8 (or 8¼) x 14 inch. That seems a bit big for a 12.5cm lens.
From Ernemann, I would expect your camera to be a Bob (with rounded ends) or a Heag (square ends). Maybe the Bob 0:
camera-wiki.org
(and page 16 of that 1924 catalogue)
You might try comparing the style of fittings (struts, viewfinder, the little catches you pull the lens carriage out with, winding key, etc) with photos of examples; in that catalogue, at Flickr, Camera-wiki, ...
There is this other catalogue, at ''Cineressources'':
Ernemann Kameras sind die Besten! (10 MB of it)
That's not dated, but they describe the Bob III as new, so it's probably about 1904. The Bob 0 doesn't exist yet. You can see the style of the shutters and brilliant finders is visibly a bit more antiquated than in the '24 catalogue.
This helps: they have a periscopic lens (listed as an option for the Bob I) but they call it 'Rapid-Detektiv-Periscop', not Doppel-Objektiv. So maybe it's safe to say your camera is later than 1904.