The
vivitar 400mm f5.6 made by tokina comes in two versions. The second later version is evidently the
tokina RMC 400mm f5.6 with a TX mount. The first version is interesting because it seems to be a custom design. Although there are also two versions of the tokina RMC 400mm f5.6, and the first version also has a tripod mount like the first version viv, it's not the same lens - different size, body, structure. I don't know if the toks are optically different, the vivs are: 8 elements for the V1, 5 for the V2.
I think the more sophisticated V1 is slightly better. K3.
My standard crop from test pic of the castle turret, f8 IIRC.