Hi Roger,
I am surprised no one has mentioned it yet, but if you have a leaf back of the right model, then C1 is free. Download it from the website and in the registration window you choose DB instead of trial, and it will develop your Leaf files, and shoot tethered, the camera is the dongle. I am pretty sure the Aptus 75 qualifies, but I am sure Yaya will be able to confirm this either way.
Cheers,
Jason.