HEAD MOUNTED DISPLAYS
A head mounted display usually includes both the display device itself and some form of head tracking to measure the position of the users head with respect to fixed space.
The display needs to present an image for each separate eye. If only a 2-D image is required either a single screen or other display device may be used or the same image may be applied to each eye's display. For 3-D images, a different picture is suppied to each separate viewing device.
To keep weight and moment of inertia low, the display devices must be kept small and close to the user's head. However, the eye cannot focus at such an extremely short range on two separate views. To overcome this, wide angle optics are used to change the apparent location of the pictures.