Who manufactures Rokinon binoculars?

They are Chinese made as are most of the binoculars on the market today. This includes companies such as Nikon, Bushnell, Tasco Swift etc. Some have Japanese made binoculars but they are the high end of the product line.Only Zeiss, Leica, Swarovski and Steiner of the larger makkers are European made.
Chinese binoculars are made to a price. The party requesting them gets what they pay for. Those with exceptional quality control are very good instruments. The only way to really tell is to look through a pair. If you like them buy them. The price they sell for don't expect brilliant performance. Nikon and Leupold have some inexpensive Chinese made units that are backed by good warranty