If you already have a ballhead, you can use something like this: Nodal Slider
This page: RSS Tutorial
or this: Smug Mug Tutorial
will show you how to find the points where there is no parallax for your lenses.
If you already have a ballhead, you can use something like this: Nodal Slider
This page: RSS Tutorial
or this: Smug Mug Tutorial
will show you how to find the points where there is no parallax for your lenses.