One trick that I use, especially if I'm going to do an image with DOF, I'll use the virtual camera as the base size to start from. For instance, if there is a human figure in the scene, I'll scale the figure until the "camera" is the size of a real camera as compared to the figure. (Does that make sense to anyone but me? Lol!) Then I can scale everything else in the scene to the figure, and everything should come out right. This really helps with DOF, but it can be used with any scene.

HTH,

Mike