The focal plane masks include a masks with all the slits and slots situated at the focal plane of the telescope itself and a decker mask that stop light from different observational modes. The decker mask contains also a HWP for polarimetry mode that rotates in order to get more accurate polarimetry. Thus, the focal plane mecahnisms include two translation stages inserting focal plane and decker masks into the optical path and a rotation mechanism rotating the HWP. We used the translation stages adapted from Jeff Julian models used in Flamingos-II. The design of the these mechanisms require carefull optimizations because of the reduced space before the bulhead. First designs show the feasability of focal plane system. Detailed analysis of these mechanisms are in getting to its end and will be ready in the near future for fabrication. We show a overall picture of the system.