What a strange and exciting time we live in! This is the new Tamron 100-400mm lens for full-frame DSLRs, in a Canon EF fit, mounted on the new Sony A7R III mirrorless camera, via a Sigma MC-11 adapter! Talk about worlds colliding! And it actually works too.
(disclaimer: we've initially reviewed the lens on a Canon 5DS R)
Read our in-depth Tamron 100-400mm F/4. 5-6. 3 Di VC USD review