COSINA filed a patent describing 50mm F1.5 with a variable soft – focus effect . [Title of invention] Imaging lens Focal length (mm): 50.5 F number: 1.562 Angle of view (degree): 46.311 Image height (mm): 21.633 Lens length (mm): 76.576 Back focus (mm): 31.879 Fig. 1 Fig . 2. Fig. 5.