[luxtpm]

and its extreamly easy to implement,

just keep game fov equal to fov the screen takes from your eyes(detected by trackir)

then in order to make objects smaller or bigger change the size of the virtual world keeping distance constant(with spheric coordinates)(instead of changing fov since you are keeping fov equal to the fov the screen takes from your eyes)

with the realistic size you see to few of the virtual world, then press a buttom programed to reduce to half the size of the virtual world