M42 MOUNT SPIRAL: LOMO OKC1-50-1, OKC1-50-3, OKC1-50-6 50mm 50mm F2 (OCT-18 mount) OKS1-50-1, OKS1-50-3, OKS1-50-6

https://spiral-m42.blogspot.com/2022/02/lomo-okc1-50-1-okc1-50-3-okc1-50-6-50mm.html