This particular lens has a maximum focal length of 50 mm and a minimum focusing distance of 0.45 m. If you want to use a filter on the lens, then the filter size is 77 mm.
From Photospecialist
Samyang VDSLR 50mm T1.5 MK2 Canon EF
DigiBroadcast
Samyang Vdslr 50mm T1.5 Mk2 Canon Ef
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