OrthographicCamera vs. HiDPI (device pixel ratio)

1. A PerspectiveCamera will produce the same view of a scene independently of the DPR of the screen. The OrthographicCamera, however, produces a smaller subset of the scene on a screen with DPR=1 than one with DPR=2, for instance. 

This can easily be seen by running the "view3d" example on different DPR and comparing the ortho and perspective views.