Both the *.vf files and *.sfvidcap files are produced by Sony Vegas so it is likely only this program can somewhat transform one to another. No 3rd party software is known to us that could otherwise perform VF to SFVIDCAP conversion.
Convert Vegas Movie Studio project to Sony Vegas video capture file.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert vf to sfvidcap on Windows
A set of professional tools for broadcast production by Sony
Convert from vf file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.