How can I untar a sub directory?

Suppose I have a tar that contains:

/                # Root directory
/level1/         # A sub directory
/level1/a.file
/level1/b.file
/level1/...      # The rest

How can I do something like tar -xf that would untar the contents level1/ like this:

/a.file
/b.file
/...       # The rest 

As long as it involves a simple sub-directory like my original question, I found I can do this:

tar -xzf mytar.tgz --strip-components 1

tar xf mytar.tar
mv /level1/* .