EYE BOX – Non Pupil forming Head/Helmet Mounted Displays

Art Hastings Jr12/11/2006

Head/Helmet Mounted Display (HMD)

HMD is a device intended to present virtual image of a microdisplay to the user at comfortable viewing distance and magnification

Applications: Military, Medical, Gaming

HMDs

eMagin 3D Visor HMD

VSI F-35 HMDS

Pupil Forming vs Non Pupil Forming

Pupil Forming – real exit pupil formed where the design eye location is. Exit pupil can be measured as luminance profile

Non Pupil Forming – no real exit pupil formed, must use performance parameters to determine the volume where the user’s eye must be palce

Non Pupil Forming Performance Parameters

Field of View (FOV): the FOV viewable by the user at a given eye location

Resolution: the Contrast Transfer Function (CTF) at a given eye location

Field of View

The FOV the user can achieve at a given eye location limited by vignetting of off axis field angles

This will be limited by the eye relief and the FOV of the system

FOV limitations

Eye must rotate to view off axis field angles Eye point of rotation located 10mm

behind pupil Will cause translation of pupil

As the eye translates out of Eye Box the user will move eye closer to the system (effectively decreasing the Eye Relief)

Eye Relief (ER) effect on viewable FOV

Pupil placed at ER resultingin vignetting of off axis fieldangles (lose FOV at edges)

Eye point of rotation placed at ERresulting in reduced clearance betweenuser’s eye and the HMD, but vignetting minimized

Resolution: Contrast Transfer Fucntion (CTF)

CTF: measurement of contrast for a given spatial frequency square wave pattern

Example of square wave pattern displayed by HMD

Contrast frequency( )Max MinMax Min

CTF will vary with pupil position

Horizontal and Vertical CTF both measured as function of pupil position

Cutoff at 50% of CTF at ideal pupil position

-67

-65

-63

-61

-59

-57

-55

-53

7

6

5

4

3

2

1

0

-1

-2

-3

-4

-5

-6

-7

00.10.20.30.40.50.6

mm

mm

Horizontal CTF vs Pupil Position

0.5-0.6

0.4-0.5

0.3-0.4

0.2-0.3

0.1-0.2

0-0.1

-67 -66 -65 -64 -63 -62 -61 -60 -59 -58 -57 -56 -55 -546

5

4

3

2

1

0

-1

-2

-3

-4

-5

-6

mm

mm

Vertical CTF vs Pupil Position

0.5-0.6

0.4-0.5

0.3-0.4

0.2-0.3

0.1-0.2

0-0.1

Eye Box

The eye box of the HMD is the volume where the user can place his pupil and achieve the full FOV for the system and see the full resolution of the system.