When tool handles are set to 'Advanced' (within the 'Preferences' or 'Tool Pipe'), additional handles become visible allowing users to interactively adjust camera setting in the viewport (mouse over the above image for handle reference). The handles are--
1.) Adjust 'Focal Length'/'Field of View'.
2.) Adjust F-Stop for Depth of Field.
3.) Adjust 'Convergence Distance'.
4.) Adjust 'Focus Distance'.
5.) Parallax Offset Difference value (distance between items for left & right eye in final rendered frame) expressed as percentage of frame width. Users can drag the handle around the scene to get an idea how far apart elements will appear on the screen when rendered as a stereo image. Generally speaking, for comfortable viewing users will want to keep the sum of the values for the closest elements in frame to the farthest elements 5% and under. Adjustments can be made to 'Interoccular Distance' and the 'Convergence Distance' options to help in obtaining this result.