I have a Tamron 90mm with a 1:2 magnification. If I use a bellows will that make it 1:1? I know I can buy an extension but I also what to know if I can get 1:1 magnification with only the bellows without the extension ring.
Yes, a bellows set should be able to give you 1:1, unless it's too deep when collapsed. In that case, it's not that you can't get up to 1:1, but that you won't be able to get down to 1:1 with the lens nominally adjusted to infinity focus; your magnification will always be greater than 1:1. In both cases (the dedicated Adaptall extension tube and the bellows) you will lose actual infinity focus.