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
Famous quotes containing the word eye:
“Often on bare rocky carries the trail was so indistinct that I repeatedly lost it, but when I walked behind him I observed that he could keep it almost like a hound, and rarely hesitated, or, if he paused a moment on a bare rock, his eye immediately detected some sign which would have escaped me. Frequently we found no path at all at these places, and were to him unaccountably delayed. He would only say it was “ver strange.””
—Henry David Thoreau (1817–1862)
“Like a wild stranger out of wizard-land
He dwelt a little with us, and withdrew;
Black and unblossomed were the ways he knew,
Dark was the glass through which his fire eye shined.”
—Edwin Arlington Robinson (1869–1935)