Dynamic range
The retina has a static contrast ratio of around 100:1 (about 6 1/2 stops). As soon as the eye moves (saccades) it re-adjusts its exposure both chemically and by adjusting the iris. Initial dark adaptation takes place in approximately four seconds of profound, uninterrupted darkness; full adaptation through adjustments in retinal chemistry (the Purkinje effect) are mostly complete in thirty minutes. Hence, a dynamic contrast ratio of about 1,000,000:1 (about 20 stops) is possible. The process is nonlinear and multifaceted, so an interruption by light nearly starts the adaptation process over again. Full adaptation is dependent on good blood flow; thus dark adaptation may be hampered by poor circulation, and vasoconstrictors like alcohol or tobacco.
Equivalent Resolution
Roger N. Clark estimates human vision resolution to be equivalent to 576 megapixels (24000 x 24000 pixels) for a 120 degree field of view. Extensive background, assumptions, and calculations are available at http://www.clarkvision.com/imagedetail/eye-resolution.html
However, it must be noted that the human eye itself has only a small spot of sharp vision in the middle of the retina, the fovea centralis, the rest of the field of view being blurry. The angle of the sharp vision being just few degrees in the middle of the view, the sharp area thus barely achieves even a single megapixel resolution. The experience of wide sharp human vision is in fact based on turning the eyes towards the current point of interest in the field of view, the brain thus preceiving an observation of a wide sharp field of view.
The narrow beam of sharp vision is easy to test by putting a fingertip on a newspaper and trying to read the text while staring at the finger tip – it is very difficult to read text that's just some centimeters away from the finger tip.
posted by Martin Crosbie @ 7:03 AM
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