Capturing can only be done over firewire from tape based cameras. Why that convoluted workflow from digital to analog and back to digital, when you can do it in a single step? Or are you phrasing your question incorrectly? Look here: Adobe Forums: A glossary of video terms
Capture is nothing more than digital data transfer from camera to disk. Nothing is changed during transfer.
Let me clarify a bit.
I am trying to capture video from my handycam which has an internal drive. Sony decided not to put a firewire out on this model so this connection is not an option for me. I have the video out from the handycam going directly to my blackmagic capture card. The audio, however, has to go from the RCA output from the handycam through the Rolls audio converter to convert th consumer level stereo RCA signals to balanced XLR. I have the XLR left and right out from the audio device going to the analog channel 1 and 2 inputs of the blackmagic card.
You can't capture from that camera. EOS.