When moving around with the middle mouse button, the field moves according to my own viewpoint. This is inconvenient because it makes looking at the far side of the field difficult. Moving the mouse down while holding the middle button also has the side effect of zooming in on the bottom edge, while zooming in by spinning the mouse wheel does not always go far enough towards the far edge. The current system even makes the camera slip through the floor when using a low angle. I think it would be better to lock the camera on its height above the field while holding the middle mouse button.
Move camera by field's axes