Virtual reality attachment for a head mounted display

1. An apparatus to reconfigure a mode of operation of a head mounted projection display for augmented reality, comprising:

a housing having a mechanical attachment or a rotating attachment; and

a freeform prism within the housing wherein the mechanical attachment removably attaches the housing to the head mounted projection display such that the projector of the head mounted display projects an image into the freeform prism that is at least partially redirected toward an eye of a user through the viewing lens of the head mounted projection display when the housing is attached to the head mounted projection display by the mechanical attachment and wherein the rotating attachment allows the housing to move between a first position wherein the projector of the head mounted projection display projects an image into the freeform prism that is at least partially directed toward the eye of the user through the lens of the head mounted projection display and a second position wherein the projector of the display does not project an image into the freeform prism while the housing is attached to the head mounted projection display.

2. The apparatus of claim 1 , further comprising a diffuse reflecting screen mounted to a portion of the freeform prism such that said projected images are brought to focus upon said diffuse reflecting screen.

3. The apparatus of claim 1 , wherein when the housing is in the second position the freeform prism does not interfere with the projected image of the head mounted projection display.

4. The apparatus of claim 1 , wherein the at least one movable mechanical linkage comprises a feature to attach or detach the housing to the outer surface of the head mounted display.

5. The apparatus of claim 1 , wherein the freeform prism includes a first section and a second section such that the first section of the freeform prism is adjacent the projection aperture of the head mounted projection display and the second section of the freeform prism is adjacent to the at least one viewing lens of the head mounted projection display when the image is projected into the freeform prism.

6. The apparatus of claim 5 , further comprising a diffuse reflecting screen mounted to the freeform prism in a position such that images brought to focus upon said diffuse reflecting screen and light reflected from said screen is directed back to the eye or eyes of a user to view the projected image.

7. The apparatus of claim 1 , wherein the mechanical attachment is selected from the group consisting of: a spring, a clip, a clamp, magnets, snaps, hooks and fasteners.

8. The apparatus of claim 1 , wherein said freeform prism is a solid prism having total internal reflection.

9. The apparatus of claim 1 , wherein the freeform prism is hollow with internally reflective surfaces.

10. The apparatus of claim 1 , further comprising a corrector prism fitted to a surface of the freeform prism and a window in the housing to mix images form the projector with light from the outside world to provide a see through augmented reality mode.

11. An apparatus to reconfigure a mode of operation of a head mounted projection display having an image projector and at least one viewing lens, comprising:

a housing having a mechanical attachment or a rotating attachment; and

a freeform prism having a narrow end and a wide end located within the housing wherein a diffuse reflecting screen is mounted adjacent the wide end wherein the freeform prism has a shape so that images entering the narrow end are brought into focus on the diffuse reflecting screen, and wherein the mechanical attachment removably attaches the housing to the head mounted projection display such that the projector of the head mounted display projects an image into the narrow end of freeform prism that exits the wide end that is at least partially redirected toward an eye of a user through the viewing lens of the head mounted projection display when the housing is attached to the head mounted projection display by the mechanical attachment and wherein the rotating attachment allows the housing to move between a first position wherein the projector of the head mounted projection display projects an image into the narrow end of the freeform prism that exists the wide end that is at least partially directed toward the eye of the user through the lens of the head mounted projection display and a second position wherein the projector of the display does not project an image into the freeform prism while the housing is attached to the head mounted projection display.

12. The apparatus of claim 11 , wherein when the housing is in the second position the freeform prism does not interfere with the projected image of the head mounted projection display.

13. The apparatus of claim 11 , wherein the mechanical attachment is selected from the group consisting of: a spring, a clip, a clamp, magnets, snaps, hooks and fasteners.

14. The apparatus of claim 11 , wherein said freeform prism is a solid prism having total internal reflection.

15. The apparatus of claim 11 , wherein the freeform prism is hollow with internally reflective surfaces.

16. The apparatus of claim 11 , further comprising a corrector prism fitted to a surface of the freeform prism and a window in the housing to mix images from the projector with light from the outside world to provide a see through augmented reality mode.

17. A system, comprising:

a head mounted projection display having at least one image projector and at least one viewing lens;

a housing having a freeform prism attachable to the head mounted projection display; and

a mechanical attachment or rotating attachment to place the at least one image projector in optical communication with the freeform prism wherein the system is in an augmented reality mode when the head mounted display projects an image and receives a retroreflected image through the at least one viewing lens and wherein the system is in a virtual reality mode when the projector is in optical communication with the freeform prism and the image from the projector is directed into the freeform prism and output from the freeform prism through the at least one viewing lens.

18. The system in claim 17 , further comprising:

a corrector prism fitted to the surface of the freeform prism wherein the system is in a see through augmented reality mode when the image from the projector is directed into the freeform prism and an outside light is directed through the corrector prism into the freeform prism simultaneously.