|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 remained in place while the front element group could easily be exchanged by another since it was fixed on a special fast mount. This allowed for a range of focal lengths.
- 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
- Some commentators were very critical of this approach: "Occasionally, for some reason, a designer will try the effect of combining two dissimilar cemented components about a central stop. It is hard to see the virtue of such an arrangement, except perhaps as an economy measure." (Kingslake, Rudolf  A history of the photographic lens. London: Academic Press, p. 102).