Capture One version 12.1 has discontinued tethering support of all the Firewire 800 and 400 digital backs. These are all the Leaf Aptus DB's and the Afi-1 and 11 plus DM40,33,28 and 22.
Support informed me: "Capture One 12.1.0 and later breaks tethering support for Aptus.
This means the latest release that incl Aptus tethering support is 12.0.4. The reason for discontinued tethering is the old firewire drivers that can no longer be maintained and would require a complete rebuild. Sorry about this."
A great pity as Capture One continues to add more digital DSLR and mirrorless cameras to broaden it's appeal, that it should drop 'Phase One' MamiyaLeaf digital backs.
David Taylor
Dorset UK