Will the mount work with a tamron 18-400 mm lens on a canon camera, need it to fit on a Sony a7iii
No, this mount adapter is made to put Sony A mount lenses on a Sony E mount camera. If you are looking to put Canon EF lenses on a Sony E mount body (like the a7 III), this is the mount you're looking for. Viltrox or Sigma brand. Both will allow you to use your Tamron lens on the Sony camera. Thanks for your question!