|1919 advertisement for the lens kit scanned by Uwe Kulick (Image rights)|
Dr. Staeble's Polyplast-Satz was a lens kit for folding cameras. It allowed to assemble lenses by mounting one back element on the back of a shutter/iris assembly, and a front elements group on the frontside of the same shutter. The back element stayed fixed, the front element group could easily be exchanged by another since it was fixed on a special fast mount.
- The advertisement above mentions the famous "Belichtungstafel nach Dr. Staeble" which could be ordered from Staeble for 50 Pfg. Here is a link showing an example of that written exposure aid of times before EVs could be measured by everyone with meters:
Belichtungstafel nach Dr. Staeble at Fotoamateure Teublitz 
- Optisches Werk Dr. Staeble & Co. G.M.b.H Muenchen. pp. 32-36: 7.5, 10.5, 12, 13.5, 16.5, 19.5, 22, 26, 32 1912 Catalogue extracts at www.cameraeccentric.com