The Eye
A brief review of how the eye forms an image will aid in understanding the VRD.
A point source emits waves of light which radiate in ever-expanding circles about the point. The pupil of an eye, looking at the source, will see a small portion of the wavefront. The curvature of the wavefront as it enters the pupil is determined by the distance of the eye from the source. As the source moves farther away, less curvature is exhibited by the wavefronts. It is the wavefront curvature which determines where the eye must focus in order to create a sharp image.
If the eye is an infinite distance from the source, plane waves enter the pupil. The lens of the eye images the plane waves to a spot on the retina. The spot size is limited by the aberrations in the lens of the eye and by the diffraction of the light through the pupil. It is the angle at which the plane wave enters the eye that determines where on the retina the spot is formed. Two points focus to different spots on the retina because the wavefronts from the points are intersecting the pupil at different angles.
Neglecting the aberrations in the lens of the eye, one can determine the limit of the eye's resolution based on diffraction through the pupil. Using Rayleigh's criteria the minimum angular resolution is computed as follows:
| Where |
|---|
| D = diameter of the pupil |
| lambda = wavelength of light |
Read more about this topic: Virtual Retinal Display
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“Passing away, saith the World, passing away:
Chances, beauty and youth sapped day by day:
Thy life never continueth in one stay.
Is the eye waxen dim, is the dark hair changing to gray
That hath won neither laurel nor bay?”
—Christina Georgina Rossetti (1830–1894)
“Mine ear is much enamoured of thy note;
So is mine eye enthrallèd to thy shape;
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On the first view to say, to swear, I love thee.”
—William Shakespeare (1564–1616)