Chinese PLA Unknown Experimental Panoramic Gas Mask (MF-18?)

If someone has more info than me, please fill me in. UPDATE: It is come to my attention, that this mask is identical to a model known as the MF-15C, with the main differences being the valve assembly off the FMJ09 (produced by a ’Plant 908’) and the recessed panoramic lens with optical insert mounts. The original seller references the mask as being called the ’MF-18’, but I have found no sources confirming this. The markings on the frames of the eyepiece confirm the mask was produced by the Shanxi Xinhua Chemical Co., the same company that produces the MF-11(FMJ05), MF-12 (FMJ06A), MF-14, and 15 masks, as well as others for the PLA. Source: